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Influences Of Interoperative Experience And Age On Recovery Of Visual Function Following Two-Stage Lesions Of The Striate Cortex
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Influences Of Interoperative Experience And Age On Recovery Of Visual Function Following Two-Stage Lesions Of The Striate Cortex
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INFORMATION TO USERS
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Xerox University Microfilms
300 North Z eeb Road
Ann Arbor, Michigan 48106
74-17,337
D R U Denise 1947**
INFLUENCES OF INTEROPERATIVE EXPERIENCE AND
AGE ON RECOVERY OF VISUAL FUNCTION FOLLOWING
TWO-STAGE LESIONS OF THE STRIATE CORTEX.
University of Southern California, Ph.D., 1974
Psychology, experimental
University Microfilms, A X ER O X Company, Ann Arbor, Michigan
i
i
INFLUENCES OF INTEROPERATIVE EXPERIENCE AND
AGE ON RECOVERY OF VISUAL FUNCTION
FOLLOWING TWO-STAGE LESIONS OF THE STRIATE CORTEX
by
Denise Dru
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(Psychology)
February 197^
UNIVERSITY O F SO U TH ER N CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANGELES, CALIFORNIA 9 0 0 0 7
This dissertation, •written by
Denise Dru
under the direction of h.Q .r . . . Dissertation Com
mittee, and approved by all its members, has
been presented to and accepted by The Graduate
School, in partial fulfillm ent of requirements of
the degree of
D O C T O R OF P H IL O S O P H Y
'In
Dean
Date < Q j ^ . l y & l J : 3 . U j 3 % 3 .
DISSERTATION COMMITTEE
Chairman
DEDICATION
This dissertation is dedicated to my mother,
Mrs. Valerie Draghiceanu.
ACKNOWLEDGEMENTS
I wish to acknowledge that this project was conducted
at: the Huntington Institute of Applied Medical Research,
Pasadena, California, whose facilities were made available
through the efforts of Mr. Leoni Bullara, Mr. Mel Ortmann
and Dr. C. Hunter Shelden.
I wish to express my appreciation to my good friends
a-fc the Tute, Ms. Eileen Curry, Ms. Rita Coveney, Mr.
Leoni Bullara and Dr. William F. Agnew for their help and
loan of equipment. To Eileen, I give a special thanks for
the many chalupa dinners. I thank also Mr. Michael
Williams, Mr. John Herr, Ms. Susan Stevens and Mr. Lewis
Tobias for their aid in the completion of this project. I
also wish to thank Ms. Carolyn Burnham for the typing of
this manuscript.
Another person to whom I am greatly indebted is Mr.
Michael "Pooh" Danley. I thank him for the photography,
for the design and fabrication of the constant current
generator, for the many hours of help and for his
unshakable friendship.
I am greatly indebted as well to my sister, Ms.
Valerie Triff, for her encouragement and support through
out: my graduate years. I thank her also for motivating me
to enter medicine.
iii
I thank the members of my dissertation committee,
Drs, James Birren and Caleb Pinch, for their guidance and
support.
My greatest thanks goes to Dr. James Walker, my
friend and adviser, for his patience and encouragement. He
is truly responsible for my attaining this degree.
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS.................................... iii-iv
LIST OF TABLES.................................. vi
LIST OF FIGURES.................................. vii
ABSTRACT ........................................ viii-ix
Chapter
I. INTRODUCTION............................ 1
II. METHODOLOGY............................ ^
III. RESULTS................................ 66
IV. DISCUSSION.............................. 79
REFERENCES...................................... 93
v
LIST OF TABLES
Table Page
1.
Mean Percentage of Cortical Destruction. • . . . 67
2. One-Way Analysis of Variance for Extent of
Cortical Damage. .......................... . , 68
3.
Median Learning and Median Retention Scores
for Young and Old Animals. ........
4. Kruskal-Wallis Analysis of Variance for
Preoperative Learning of Young Animals . . . . 70
5.
Kruskal-Wallis Analysis of Variance for
Preoperative Learning of Young and Old,
Restrained and Unrestrained Groups . . . . 72
6. Kruskal-Wallis Analysis of Variance for
Postoperative Retention of Young Animals .
. . 7^
vi
LIST OP FIGURES
Figure Page
1. The two-choice visual discrimination apparatus
for testing ability to differentiate
horizontal-vertical discriminanda..............h6
2. Discrimination chamber showing discriminanda
in right and left positions................... ^8
3. Scrambled shock generator used to deliver
constant current pulses to the discrimination
grid................ ^9
Diffuse light chamber used with animals exposed
to diffused illumination ........... 53
5. Apparatus for transport of restrained subjects
through a patterned visual environment .... 53
6. Close-up of subject in place in restraining
holder............ 5^
7. Restraining holder for restriction of motor
movement.......................................5^
8. a. Patterned visual environment used with
animals allowed free movement during exposure
periods,
b. The circular alley is partitioned into
units for individual animals.............. , 56
9. a.-f. A comparison of minimal and maximal
extent of cortical damage for each of the six
groups of animals...............................59
10. Individual retention scores for trials to
criterion for all groups............. 77
11. Individual retention scores for errors to
criterion for all groups ..... ......... 78
vii
ABSTRACT
Six groups of male hooded rats, four composed of
three-month old animals and two composed of twenty-four
month old animals underwent two-stage lesions of the
striate cortex. During the eleven day interoperative
period, subjects were differentially exposed to visual
stimulation four hours daily. The remaining twenty hours
were spent in total darkness. Interoperative visual
experience was as follows: Group I was maintained in
total darkness interoperatively, Group II was exposed to
diffuse light, Groups III and V (young and old) were
passively transported through a patterned visual environ
ment, Groups IV and VI (young and old) were allowed free
movement during exposure to the patterned visual environ
ment. Following the second surgery, the animals were
tested for retention of a preoperatively learned
horizontal-vertical pattern discrimination. Recovery of
pattern vision occurred only in animals allowed locomo
tion during exposure to patterned stimuli. Old animals
demonstrated less recovery than young animals. The
significance of self-produced movement to visual recovery
is in accord with findings from neonatal vision depriva
tion studies and sensory-motor rearrangement experiments
viii
where self-produced movement during exposure to a visual
environment was necessary for visual-motor development and
adaptation.
ix
CHAPTER I
INTRODUCTION
In the context of the following discussion, the
phenomenon of recovery of function takes place in the CNS
when a structure represented bilaterally in the brain is
removed in two separate unilateral operations. If the
structure is removed in two stages with a certain number
of days intervening between surgeries, other areas of the
brain seem to take over lost function. If the same
structure is bilaterally removed in one operation, the
resulting neural impairment is more severe and sometimes
permanent. Thus, certain functions which would normally
be lost following a bilateral single-stage ablation may
be spared if the same tissue removal is performed in two
or more stages.
The exact nature of the recovery process is not
known. It has been established, however, that the extent
of recovery is dependent both upon the type of behavior
being spared and the type of neural tissue being removed
(LeVere, 1969). Furthermore, there are two factors which
appear to be critical to the occurrence of functional
recovery. First, there must be a certain amount of time,
greater than one week, between two-stage lesions in order
1
for a specific function to be recovered (Stewart and Ades,
1951). Second, there must occur some degree of non
specific sensory stimulation during the interoperative
period (Petrinovich and Bliss, 1966; Petrinovich and
Carew, 1969; Stewart and Ades, 1951. Thompson, i960).
For example, if animals undergoing two-stage lesions of
the visual cortex are kept in the dark between surgeries,
loss of visual function occurs just as though the ablation
was performed in one stage. On the other hand, animals
receiving various types of visual stimulation during the
interoperative period recover visual capacity to varying
degrees.
The nature of the interoperative activity is the
subject of this research. Exactly what types of inter
operative sensory input are required for complete
recovery of visual function remains in question, but some
clues may be provided in two parallel areas of research;
neonatal visual deprivation studies and visual-motor
rearrangement experiments.
Neonatal Visual De-privation Studies
Neonate animals raised in absolute darkness or in
diffuse, unpatterned illumination do not develop normal
vision and may never achieve the ability to discriminate
forms or patterns (Riesen, 1973)* More significant is the
fact that young animals exposed daily to normal visual
environments do not develop normal visual capacity if they
are restrained during the exposure periods (Fish and
Robinson, 1971; Held and Hein, 1963; Meyers, 196^;
Riesen, 1965; Riesen and Aarons, 1959)• Thus, visual
stimulation alone is not sufficient for normal development
of the visual system. Instead, bodily movement during
visual exposure periods appears fundamental to normal
development of visual capacity and visual-motor coordina
tion. A similar finding has been obtained in studies of
sensory rearrangement in humans.
Visual-Motor Rearrangement Experiments
Many studies have been conducted to determine in what
manner a subject adapts to prismatic distortion of the
visual field. Initially, application of prism eyeglasses
results in gross errors in visual-motor coordination.
However, the subject can adapt to such distortion until
little if any visual-motor incongruency exists (Harris,
1963, 1965; Held and Gottlieb, 1958; Held and Hein, 1958;
Held and Schlank, 1959)- The degree to which adaptation
occurs is highly dependent upon the type of exposure the
individual has to the visual environment. It appears that
complete visual-motor reorganization to prismatic distor
tion occurs only if the subject is allowed bodily move
ments during exposure to the visual environment (Held and
Gottlieb, 1958; Held and Hein, 1958).
4
Such evidence implies that related processes
underlie both the original development of visual-motor
coordination and the reorganization of visual-motor
coordination under conditions of sensory distortion. It
is proposed here that this relationship extends to visual-
motor recovery of function following serial lesions.
RECOVERY OF FUNCTION* THE PHENOMENON
The phenomenon of recovery of behavioral function
following damage to the brain has been observed in a
variety of mammalian species in both neocortical and non-
neocortical systems and with both learned and unlearned
forms of behavior. The course of recovery in brain
damaged animals usually involves an initial period during
which there is an inability to perform specific tasks.
This inability is gradually overcome by extended practice
or relearning of necessary behavioral functions (Dicara,
1970 j Lynch, et al.. 19691 Orlowsky and Glussman, 19&9l
Schmaltz and Isaacson, 19681 Teitlebaum and Epstein, 1962).
Many studies have indicated that for certain behav
ioral functions, young animals show a greater potential
for recovery than adult animals with identical forms of
brain damage (Stewart and Riesen, 1972). However,
amelioration of behavioral deficits in adult animals can
be induced if damage occurs serially rather than simul
taneously. Thus, when a structure represented bilaterally
in the brain is lesioned in two separate operations with
a certain number of days intervening between surgeries,
other areas of the brain seem to take over lost function.
If the same structure is bilaterally lesioned in one
operation, the resulting deficits in behavior are more
severe and sometimes permanent. Consequently, certain
functions which would normally be lost following bilateral
single-stage removal, or which could be regained only
after a long recovery period, may be spared or more
quickly recovered if the same neural tissue is removed in '
successive stages.
For some functions, multiple-stage lesions acceler
ate the time course of recovery (Glick and Greenstein,
1973; Glick and Zimmerberg, 1972; Petrinovich and Bliss,
1966; Petrinovich and Carew, 1969). For other functions,
such lesions initiate recovery of behaviors which would
normally be abolished by single-stage lesions (Finger,
et al.. 1971; Howe and Smith, 1973).
The mechanisms by which recovery takes place are
under investigation but the exact nature of the process
remains unknown. Certain factors have been identified as
critical to the occurrence of functional recovery follow
ing serial lesions. The extent of recovery is known to be
dependent upon: 1) the type of behavior being spared, i.e.
learned vs. unlearned (LeVere and Weiss, 1973); 2) the
type of neural tissue being removed, i.e. neocortical
vs. nonneocortical (Butters et al.. 1973; LeVere and
Weiss, 1973); 3) the length of the interoperative inter
val (Isaac, 196^} Stewart and Ades, 1951); and the type
of sensory stimulation which occurs during the interopera
tive period (Petrinovich and Bliss, 1966; Petrinovich and
Carew, 1969; Thompson, i960). It is with the last of
these determinants that this research is concerned.
Nonneocortical Lesions and Unlearned Behaviors
Although neocortical areas of the brain are typically
considered to have the greatest potential for functional
plasticity, recovery after serial lesions has been ob
served in neurological systems considered innate and un-
modifiable. In an early study by Adametz (1959).
functional recovery was demonstrated in cats following
serial-stage lesions of the rostral reticular midbrain.
Animals with single-stage lesions in this area remained
comatose postoperatively until death. Animals with serial
lesions spaced three weeks apart demonstrated relatively
rapid recovery from coma and even a restitution of motor
function. Similarly, Lourie et al. (i960) found that cats
with progressive tegmental and midline thalamic lesions
were not comatose postoperatively but were instead capable
of arousal. In this case, progressive lesions developed
over a two-week period following application of alumina
gel to the neural tissue.
The occurrence of recovery of unlearned behaviors
following serial subcortical lesions may not be general
ized to all nonneocortical areas. Two-stage lesions,
spaced ten days apart, of the posterior hypothalamus of
rats failed to initiate recovery of the waking state
(LeVere, 1969). Thus, there is indication of a differen
tial potential for recovery among subcortical structures.
Nonneocortical Lesions and Learned Behaviors
A lack of potential for recovery seems to be the rule
rather than the exception for learned behaviors mediated
by limbic structures. Although the ability to acquire new
tasks postoperatively seems to be spared by two-stage
lesions of certain subcortical structures, the ability to
retain preoperatively learned behaviors is not. Stein,
et al. (1969) performed one and two-stage lesions of the
dorsal hippocampus and amygdala of Albino rats. The two-
stage lesions were separated by thirty days with a four
teen day postoperative recovery period for both groups.
Following surgery, the two-stage animals showed normal
ability to learn a variety of tasks including a succes
sive brightness discrimination, its reversal, and a
passive avoidance task. In contrast, the one-stage
animals showed marked and longstanding deficits in the ac
quisition of these tasks. Since no interoperative training
was given to animals in the two-stage group, the recovery
process was considered spontaneous. Furthermore, since
no evidence of neural regeneration was demonstrated,
other regions of the brain were assumed to take over lost
function.
In contrast to the results for task acquisition,
measures of retention of preoperatively learned behaviors
consistently fail to demonstrate savings following two-
stage lesions of the hippocampus. Isaacson and Schmaltz
(1968), using hooded rats, failed to demonstrate function
al sparing of a preoperatively learned DRL-20 task
following two-stage hippocampal lesions separated by
several weeks. The DRL task involved differential rein
forcement for low rates of responding in an operant
chamber. A response was followed by reinforcement only
if it occurred after twenty seconds of no responding.
One-stage animals received fourteen or forty-one days of
postoperative recovery while two-stage animals received
fourteen days of recovery. Two-stage lesions were
separated by twenty-seven days. Some animals received
interoperative practice on the task during the final ten
days intervening between surgeries. The results of this
study clearly indicated that bilateral destruction of the
hippocampus produced a deficit in retention whether or
not the damage was produced in one or two stages and
regardless of interoperative practice.
In a related study, LeVere and Weiss (1973) used a
hippocampally controlled behavior to evaluate the occur
rence of sparing following two-stage lesions in rats. The
task employed was a successive brightness discrimination
and its reversal, identical to that used by Stein et al.
(1969). In this case, the task was preoperatively learned
and the animals were tested for retention rather than
acquisition. The interoperative interval was fifteen days
and postoperative recovery time was five days. For one-
stage animals, postoperative recovery was five or twenty-
one days. The results failed to demonstrate sparing of
the task following serial lesions even when interopera
tive practice was allowed between surgeries. There were
no differences in retention among the one and two-stage
groups.
Thus, for the learned behaviors of DRL and spatial
reversal, no functional sparing or savings in retention
was demonstrated after two-stage lesions of the hippo
campus. Two considerations must be noted at this point.
First, the failure to demonstrate sparing of a pre
operatively learned task does not preclude the possibility
that recovery could take place if testing were extended
to some later postoperative period. Secondly, lesions of
the hippocampus necessitate destruction of the overlying
posterior neocortex and corpus callosum. Thus, visual
10
areas and interhemispheric connections are destroyed in
hippocampally lesioned animals. There is evidence that
when selective lesions of major afferent and efferent
hippocampal connections are carried out with minimal
concurrent damage to other structures, two-stage recovery
does occur (Greene et al. . 1972). Hooded rats were tested
for retention of a simple, right-left alternation known to
be affected by hippocampal lesions. Lesions of the fornix
were carried out in one or two stages with a postoperative
recovery period of two days. The interoperative interval
for the two-stage animals was twenty-seven to thirty-two
days. These animals received two sessions of interopera
tive testing four days after the first surgery and five
to eight days prior to the second surgery. The two-stage
animals did in fact demonstrate recovery of function,
showing greater retention than animals receiving single-
stage lesions.
Further evidence for subcortical regional differences
in the potential for recovery is provided in a study by
Rowe and Smith (1973). Serial removal of the olfactory
bulbs separated by thirty days had no effect upon the
subsequent mating behavior of male mice. Recovery
occurred whether or not mating experience was allowed
between surgeries. In contrast, simultaneous ablation of
the olfactory bulbs abolished mating behavior even though
11
all mice were sexually experienced preoperatively.
Neocortical Lesions and Unlearned Behaviors
In general, neocortical regions of the brain are con
sidered to have the greatest capacity for functional
plasticity. With few exceptions, recovery of function
following serial-stage lesions of the neocortex has been
consistently demonstrated for both learned and unlearned
forms of behavior and in many different cortical areas.
Some of the earliest demonstrations of functional
recovery following serial ablations of the neocortex were
carried out with monkeys. Simultaneous ablations of motor
and pre-motor areas of the cortex were found to cause
severe disorders of movement including paresis, flaccid-
ity, spasticity and loss of reflexes. When identical
lesions were spaced four weeks apart, the animals re
covered motor function. These findings were confirmed by
Ades and Raab (19^6) who performed successive-stage ab
lations of Area ^ of the.cortex of monkeys. When such
ablations were separated by a period of three to four
months, none of the usual signs of pyramidal injury were
evident. In this case, however, interoperative intervals
of one to two months proved insufficient for the occur-
I
rence of recovery.
In rats, two-stage lesions of the frontal cortex
spaced two weeks apart facilitated recovery from the post-
12
operative weight loss which normally follows bilateral
single-stage lesions (Glick and Greenstein, 1973).
Neocortical Lesions and Learned Behaviors
In this and the following sections, much evidence
will be presented to document the generality of the two-
stage recovery process to a variety of neocortical struc
tures and learned behaviors. The effects of serial-stage
lesions in the two somatosensory areas were evaluated on
acquisition of a series of tactile discriminations
(Finger et al., 1971). Blinded rats were tested in a T-
maze on five, two-choice tactile discriminations. The
interoperative interval was thirty-five days and the post
operative recovery period was one month for all animals.
Relative to the serially ablated animals, the one-stage
rats performed poorly on all tasks. An interesting vari
ation in serial-stage lesions was performed in a second
part of the experiment. One group of rats had small bi
lateral lesions placed in the somatosensory areas. These
lesions v/ere enlarged to full size thirty-five days later.
These rats acquired the tactile discriminations signifi
cantly better than did animals with one-stage lesions of
full size.
Recovery of a passive avoidance deficit occurred
following both simultaneous and successive-stage transac
tions of the frontal cerebral poles of mice, but the time
course for recovery was significantly accelerated in
animals with two-stage lesions (Glick and Zi'mmerberg,
1972). Recovery proved to be a function of time either
between the two-stage lesions or after the one-stage
lesions. Thus, animals with successive lesions performed
three weeks apart, or with one-stage lesions followed by
three weeks recovery, were equivalent in their performance,
on a passive avoidance deficit. Mice with the minimal
effective interoperative period of seven days were slight
ly worse in performance than one-stage mice with a one
week postoperative recovery period. These two-stage mice
were equivalent to the single-stage mice tested two days
postoperatively. It will become apparent later in this
discussion that two-stage lesions separated by less than
one week are equivalent to one-stage lesions in producing
postoperative behavioral deficits.
Serial lesions of the orbitofrontal areas of rats
resulted in unimpaired ability to acquire a series of
tasks including a delayed spatial alternation, a light-
dark successive visual discrimination and its reversal,
and a nonspatial simultaneous pattern discrimination
(Stein et al.. 1969). Again, animals with similar lesions
carried out in one operation performed poorly on all
tasks. The interoperative interval was thirty days and
the postoperative recovery period was fourteen days.
Similar results were obtained in the monkey with
multiple-stage lesions of the dorsolateral prefrontal
cortex (Butters et al. . 1972; Rosen and Stein, 1973)*
Monkeys were tested for retention of a spatial delayed
alternation and for acquisition of delayed response and
place reversal (Rosen and Stein, 1973). They were found
to be superior on postsurgical retention and acquisition
if lesions were carried out in several stages. Serial
lesions were performed in four stages spaced three weeks
apart. A one week postoperative recovery period pre-
ceeded testing for both multiple and single-stage
animals. On all tests, the serial-stage monkeys made
fewer errors than did the monkeys with one-stage lesions.
Thus, the phenomenon of two-stage recovery occurs in a
number of cortical areas for a variety of behavioral
functions. Under ideal conditions, the phenomenon is
almost universal with one significant exception to date.
Sequential ablation of the orbital prefrontal cortex
in monkeys does not result in functional recovery
(Butters et al.. 1973). Serial lesions were performed in
four stages spaced three weeks apart. A one week post
operative recovery period preceeded testing for both
multiple and single-stage animals. Monkeys were tested
for retention of a visual go-no go differentiation task
and for acquisition of a spatial delayed alternation and
object reversal. The serial-stage monkeys failed to show
less deficit than single-stage animals on all tasks.
These results are in contrast to results of previous
investigations on the dorsolateral prefrontal area.
Several considerations were discussed by the authors as
being relevant to the discrepancy in data. The dorso
lateral and orbital prefrontal areas are different in
function. The dorsolateral area is concerned with
spatial and mnemonic functions and connects with the
basal ganglia, cingulate cortex and temporal neocortex.
The orbital area is concerned with response inhibition as
well as mediation of aversive and aggressive behavior.
It connects with structures of the limbic system. Based
on these facts, the authors speculate that recovery may
follow sequential destruction of cortical regions
mediating sensory, motor or associative functions, but may
not follow serial destruction of regions concerned with
motivational processes. This notion is in accord with
data derived from two-stage lesions of limbic structures
where recovery of function is not consistently demonstra
ted.
Length of Interoperative Interval
Although the process of recovery has been generalized
to a variety of cortical structures and behaviors, there
are, nonetheless, certain restrictive conditions that
16
determine the occurrence of recovery following serial-
stage lesions. One such condition is the length of time
intervening between surgeries. Ades and Raab (19^6) dis
covered that a period of one to two months between bi
lateral ablations of Area k in the monkey cortex was
insufficient to preclude motor dysfunction. Extending
the interoperative interval to three and four months
resulted in amelioration of impairment and rapid
recovery.
Stewart and Ades (1951) similarly found in monkeys
that for a conditioned avoidance response to be spared
postoperatively, an interval of at least seven days must
separate the two ablations. In this case, the behavior
was an avoidance response elicited to auditory stimuli.
Surgery was performed on the auditory cortex. Inter
operative periods of less than one week resulted in
behavioral impairments equivalent to those resulting
from single-stage lesions.
Using a similar behavioral task, Isaac (196^)
trained rats preoperatively to make an avoidance response
to a change in illumination; interoperative intervals
between occipital ablations were ten, twelve or fourteen
days. A difference of two days in either direction from
the usual twelve day interoperative period had significant
effects upon the ultimate sparing of the task. Increasing
17
the interval served to increase the degree of recovery.
Decreasing the interval served to decrease the extent of
recovery.
Nature of Interoperative Experience
Perhaps the most significant determinant of the
occurrence of two-stage recovery of function is the nature
of sensory stimulation that occurs during the interopera
tive interval (Meyer et al. , 1958; Petrinovich and Bliss,
1966; Petrinovich and Carew, 1969; Thompson, i960). For
example, if animals undergoing two-stage lesions of the
visual cortex are kept in the dark between surgeries,
loss of visual function occurs just as though the ab
lation was performed in one-stage. On the other hand,
animals receiving various types of visual stimulation
during the interoperative period recover visual capacity
to varying degrees.
The nature of the interoperative activity is the
subject of this research and, as such, is treated as a
separate section.
INFLUENCES OF INTEROPERATIVE ACTIVITY
ON TWO-STAGE RECOVERY OF FUNCTION
In one of the earliest studies of tv/o-stage recovery
of function, Raab and Ades (19^6) investigated the effects
of simultaneous and successive lesions of the auditory
cortex of the monkey. When bilateral removal of the
18
auditory areas occurred in one operation, the animals
were unable to retain a conditioned auditory avoidance
response. If, on the other hand, right and left lesions
were performed in two separate operations, allowing time
for recovery from surgery in between, the habit was re
tained. The authors concluded that the first ablation
was insufficient to disrupt the conditioned response, but
that the disturbance in cortical functioning resulted in
a reorganization process which extended bilaterally. The
authors left unanswered the question of whether the re
covery occurred spontaneously or whether it depended upon
interoperative testing of the subjects.
Stewart and Ades (1951) investigated these possibili
ties again using lesions to the auditory cortex of mon
keys. They found that simultaneous bilateral ablation of
the superior temporal gyrus in the monkey resulted in loss
of a previously conditioned response to an auditory
stimulus. However, an interval of at least seven days
between the removal of the tissue from the two hemis
pheres resulted in no loss of the conditioned response.
The experimenters thought that whatever the process
responsible for recovery, it was apparently spontaneous
insofar as it took place independently of continued formal
training between surgeries.
The question of interoperative activity as signifi
cant to recovery was again raised in the study by Meyer
et al. (1958). As usual, they found that rats which had
learned a light avoidance response and which were then
subjected to simultaneous bilateral ablation of the
occipital cortex lost the habit. Corresponding lesions
performed in two stages, twelve days apart, did not abol
ish the habit. They also discovered that the environ
mental condition of the animal in the interval between
two-stage lesions was a critical factor in determining
whether or not the learned discrimination was retained.
Those rats which were kept in their home cages for eleven
days between two-stage lesions showed good retention of
the habit. Those animals which were kept in the dark for
eleven days between surgeries lost the habit. Sham-
operated controls retained the habit regardless of the
interoperative environmental conditions. The authors
concluded that reorganization was not spontaneous but was
instead dependent upon nonspecific stimulation of the
visual system during the interoperative period.
It was later observed that nonspecific stimulation
of sensory systems other than the one relevant to the
behavioral task could facilitate sparing of a conditioned
avoidance task (Isaac, 196*0. Albino rats trained pre-
operatively to make an avoidance response to changes in
illumination were then subjected to two-stage lesions of
20
the posterior neocortex. Environmental conditions were
varied during the interoperative period. The animals
received various combinations of light-quiet, dark-quiet,
light-noise and dark-noise environments sixteen hours a
day during the interoperative interval. The remaining
time was spent in darkness under quiet conditions.
Animals kept in light-noise environments recovered best,
while those kept in dark-quiet environments recovered
least. Of significance is the fact that animals kept in
dark environments but receiving auditory stimulation be
tween surgeries recovered the visual avoidance task to a
greater degree than did the dark-quiet subjects. Thus,
general or total sensory input between surgeries, whether
specific or nonspecific to the nature of the task, had
significant influence 011 the extent of recovery. Stimu
lation of both auditory and visual sensory systems pro
duced greater postoperative retention of the habit than
stimulation of either system alone. The author specu
lated that the effect of nonspecific sensory stimulation
was to increase the generalized activity level of the
reticular activating system; and thus, that the RAS was
intimately involved in the occurrence or nonoccurrence
of recovery.
The above studies indicate that for recovery of a
conditioned avoidance response (CAR), interoperative
stimulation, whether it be visual (Meyer et al.. 1958) or
auditory (Isaac, 196^), induces a reorganization which
permits serially lesioned animals to retain avoidance re
sponses which are abolished following single-stage lesions.
Still another form of nonspecific stimulation has been
found to influence sparing of avoidance responses. Using
d-amphetamine and phenobarbital as the nonspecific inter
operative stimulants, Cole et al. (1967) studies recovery
of CAR in rats following two-stage ablations of the
posterior neocortex. Avoidance responses were made to
changes in illumination. In accord with the speculations
of Isaac (196^) that the activity of the RAS was in some
way related to the occurrence of recovery, these inves
tigators used d-amphetamine and phenobarbital as pharma
cological agents which were thought to increase or de
crease, respectively, RAS activity.
Thus, it was predicted that d-amphetamine would
compensate for a reduction of RAS activity when animals
were visually deprived between surgeries. Conversely, it
was thought that phenobarbital would reduce RAS activity
during intervals when subjects were usually stimulated.
The results of the experiment confirmed these predictions.
Postoperative retention was superior when the interopera-
tive interval was spent in a lighted and noisy environ
ment except when paired with chronic administration of
22
phenobarbital (30 mg/kg/day). Postoperative retention was
poor when animals were kept in dark and quiet environments
between surgeries except when paired with chronic adminis
tration of d-amphetamine (2 mg/kg/day), when retention v/as
good.
Recovery of conditioned avoidance responses is thus
facilitated by nonspecific forms of sensory stimulation.
As will be seen, recovery of more complex discrimination
habits may require more specific forms of interoperative
stimulation.
Thompson (i960), in contrast to the above results,
found that specific practice of a response rather than
nonspecific stimulation of the cortical areas was neces
sary for retention of a black-white visual discrimination
habit. Albino rats that learned a simultaneous brightness
discrimination and were kept in their home cages for the
eleven days between two successive unilateral occipital
removals, lost the habit. The habit was retained only if
the animals were rerun to criterion between the two opera
tions. Again, one-stage lesions of the occipital area
abolished the habit.
Petrinovich and Bliss (1966), investigating this
paradox, found that either practice of the task or non
specific visual stimulation was sufficient for retention
of the black-white discrimination habit. Each of the
unilateral lesions involved less than 15 per cent of the
neocortex. The habit was spared if the rats were housed
in their normally lighted home cages or if they were given
thirty trials of practice between successive lesions.
Again, rats which were housed in darkness between two-
stage lesion lost the habit, as did rats which underwent
single-stage removals of the visual cortex. The authors
speculate that the difference between their results and
those of Thompson (i960) is due to the difference in
lesion size in the two studies. The median percentage of
neocortical destruction produced by Thompson ranged from
20.5 to 2^.2 per cent and that produced by Petrinovich and
Bliss ranged from 9.^ to 12.^ per cent.
In a later study, Petrinovich and Carew (1969) found
that when lesions involve approximately 10 per cent of the
total neocortex, nonspecific visual stimulation is suffi
cient to obtain sparing of a brightness discrimination with
two-stage lesions. If lesions involve 20 per cent of the
neocortex, specific practice of the habit between surger
ies is necessary for recovery. Again, rats remaining in
the dark during the eleven day interoperative period lost
the habit.
Using the same black-white visual discrimination,
Kircher et al. (1970) found in rats that two-stage lesions
of the posterior neocortex separated by twelve days and
involving greater than 20 per cent of the neocortex did
not facilitate recovery of this habit compared to single-
stage removals. Furthermore, in contrast to the results
of Cole et al. (1967) for visual CAR tasks, interopera
tive amphetamine injections combined with light and dark
housing conditions failed to enhance recovery. It should
be noted, however, that in previous studies using the
black-white discrimination habit, six days of postopera
tive recovery were typically allowed for both one and
two-stage groups before retention tests (Petrinovich and
Bliss, 1966; Thompson, i960). In the case of Petrinovich
and Carew (1969)* sixteen days were allowed for the one-
stage group and six days were allowed for the two-stage
group. In the present study, a twenty-four day post
operative recovery period was given the serial-stage
group. Failure to demonstrate differences between
single-stage and serial groups may have been due to the
extended recovery period given the one-stage animals.
Kircher (1970) nonetheless, suggests that successive
procedures which do not involve specific interoperative
training are unlikely to facilitate sparing of the two-
choice visual discrimination.
Lending further support to the notion that inter
operative stimulation is significant to the occurrence of
two-stage recovery of a black-white discrimination is the
study by Glendenning (1972). Rats were tested for
retention of the habit following an eleven day interopera
tive period with various types of practice during this
interval. Using large lesions of the occipital cortex,
it was found that one and two-stage animals were equiva
lent in retention when no formal training was given
interoperatively. When formal training was given and
when it involved occlusion of the eye contralateral to
the lesion, animals required more trials to relearn the
task interoperatively than did animals using the ipsi-
lateral eye or both eyes. Nonetheless, these three
groups were equivalent in postoperative retention and
superior to the one-stage animals. Again, interoperative
training was fundamental to sparing of the visual habit.
Typical of all the above studies is the fact that
visual deprivation during the interoperative period
generally precludes the two-stage recovery process.
Although the subject of much research, the nature of the
visual stimulation necessary for sparing of a visual
habit remains in question; however, possible answers may
be obtained from related research with neonatal depriva
tion discussed below.
NEONATAL VISUAL DEPRIVATION
Similar to the findings that interoperative visual
deprivation interferes with recovery of visual-motor
function are the findings that neonatal visual
deprivation interferes with visual-motor development. It
is well established, especially in cats and primates,
that neonatal animals reared in total darkness or in
diffuse light show deficits in such visual functions as
visual pursuit, depth perception, acuity and visually
guided motor behavior (Riesen, 1973). Of even greater
significance is the fact that visual stimulation during
development must be accompanied by self-produced motor
movement in order for normal visual function to be
established.
Pattern Vision with Motor Restriction
A series of studies in the area of visual depriva
tion has been concerned with the effects of motor restric
tion during exposure to pattern vision. Access to a
patterned visual environment is apparently insufficient
for development of the normal complement of visual func
tions. Riesen and Aarons (1959) raised kittens in total
darkness from birth to six weeks of age. The kittens
were then exposed to either diffused or patterned light
stimulation for one hour daily while held in a restrain
ing apparatus. Following eight to twelve weeks of such
exposure, the kittens were trained in a Yerkes-Watson box,
on either a movement or intensity discrimination. Motor-
restrained animals exposed to either diffused or patterned
environments were equivalent to normally reared cats on
27
the intensity discrimination. The restrained cats, how
ever, were never able to learn the discrimination between
a rotating and a stationary cross.
.A later study confirmed these findings in that
motor-restricted cats showed severe deficits in differ
entiating a stationary and moving dot. They required
nearly four times as many learning trials as did normally
reared animals (Riesen, 1965). Thus, in order to develop
the ability to discriminate between intrinsically and
extrinsically-produced movements in the visual field,
young animals must be permitted active movement of the
body and limbs during early development.
In another experiment, kittens were raised in the
dark up to the normal time of eye-opening (Meyers, 196^).
At seven weeks of age, the kittens were exposed binoc-
ularly to a visual environment while confined in restrain
ing boxes. Exposure periods lasted one hour per day. At
twenty-nine or thirty weeks of age, the kittens were
placed in a restraining apparatus and trained to dis
criminate between a stationary and rotating cross. The
animals responded by leg flexion which required minimal
movement through visual space. The movement-restricted
animals in this case were equivalent to normally-reared
animals in the performance of the task.
In a study by Fish and Robinson (1971)* kittens were
exposed binocularly to a visual environment but received
only monocular visual-motor experience. The kittens had
been dark-reared until six to eight weeks of age. They
were then binocularly exposed for one hour daily to a
normal visual environment while restrained in a holder.
One eye was occluded, however, during exposure periods
in which unrestricted movement was allowed. At eighteen
months of age, the cats were monocularly tested for
visual-motor abilities in an apparatus which required
the animals to negotiate a series of barriers. In com
parison to normally reared cats of the same age, the ex
perimental animals were impaired in their ability to
avoid the barriers using either eye. Deficits were
somewhat less severe, however, with the experienced eye.
Visual-motor deficits of movement-deprived animals
result from the lack of visual feedback accompanying
self-produced movements in a normal environment. Held
and Hein (1963) compared the development of visual abili
ties in kittens that had been free to locomote in
patterned light and kittens that had been passively
transported through the same environment. After several
days in the apparatus, the actively moving animals showed
visual placing, depth perception and eyeblink response to
rapidly approaching visual targets. Passively transported
animals had received equivalent visual stimulation but
29
never displayed good visual-motor coordination. These
animals were then allowed forty-eight hours of unre
stricted movement in a normal visual environment and
spatio-motor abilities began to develop. In a subsequent
experiment, one eye was exposed during active locomotion
(Hein, Held and Gower, 1970). It was found that the two
eyes could independently acquire control of movement.
When one of the eyes was permitted to view only one of
the forelimbs, that eye controlled guided reaching of
the viewed forelimb only (Hein and Diamond, 1971).
Monkeys were reared from birth to thirty-four days
in a chair which prevented sight of their bodies (Held
and Bauer, 1967). Between days sixteen and thirty-four,
each monkey was conditioned to orient its head and eyes
and to extend its limbs horizontally in the direction of
a feeding bottle when it was offered. On day thirty-
five, one arm was exposed to view and testing of visually
guided reaching was begun. Guided reaching was poor at
first but improved rapidly with subsequent visual ex
perience .
Animals allowed free movement in a visual environment
but not allowed to view limb movements demonstrate
deficits in visually guided abilities. A similar pheno
menon was demonstrated in cats. Hein and Held (1967)
raised kittens in the dark from birth to six weeks of
age. Thereafter, they received six hours of daily ex
posure to a normally illuminated room while unrestricted
in movement. During this period, the kittens wore
opaque collars which prevented their viewing their limbs
or torso. After twelve days of such experience, all
kittens displayed forelimb extension to a continuous
surface, but did not display guided placing to an in
terrupted surface. 'When a ball was dangled at the end
of a string, accurate visual pursuit was displayed but
guided reaching to the ball was markedly inaccurate.
Before normal guided reaching began to be manifested,
fifteen hours of normal unrestricted movement in a
visual environment was required. The authors point out
that the guided reaching response and the extension re
sponse, both of which are component behaviors of the
visually guided placing response, are independent sensori
motor behaviors. Thus, their development requires an
integration of sensorimotor systems which are not
necessarily the same.
Supporting this notion is the fact that motor
visual feedback is prerequisite to the development of
visually guided behaviors but is not prerequisite to the
acquisition of visually triggered extension (Hein et al.,
1970)- Dark-reared kittens were given two to twenty-six
days of stimulation by light either in a patterned en
vironment, with diffusers in front of the eyes, or with
stroboscopic illumination. All acquired the extension
response even when exposure conditions were given with
complete body immobilization. In contrast, visually
guided behavior including visual cliff descent and ob
stacle avoidance did not develop under these exposure
conditions.
Similarly, visually triggered extension could be
mediated after monocular exposure to diffused or
patterned light with either the exposed or naive eye
(Hein and Diamond, 1971). This was not true for visually
guided behaviors, again suggesting distinct mechanisms
underlying triggered and guided components of visual-
motor behaviors.
Furthermore, it now appears that components of
visual-motor coordinations are developed sequentially.
Acquisition of visually guided reaching did not occur
until after development of visually guided locomotion
(Hein and Diamond, 1972). The authors suggest that the
capacity for guided locomotion implies the existence of
a body-centered "map" of visual space in which objects
are visually localized. By this frame of reference, the
limbs, like other objects, can be visually positioned.
All previous results have indicated that the correlation
32
of visual stimulation from a forelimb with the self
produced movement of that limb is fundamental to the
development of the capacity for visually guided reaching.
In all of the studies cited above, it has been
demonstrated that motor restriction during the early
periods of perceptual development interferes with the
acquisition of visually guided behaviors. Visual stimu
lation alone is not sufficient for normal development of
the visual system. Young animals exposed daily to normal
visual environments do not develop normal visual capacity
if they are restrained during the exposure periods. A
similar finding has been obtained in studies of visual
rearrangement in humans wherein bodily movement during
prismatic exposure periods appears fundamental to visual-
motor reorganization.
VISUAL-MOTOR REARRANGEMENT EXPERIMENTS
There is evidence implying that related processes
und.erly both the original development of visual-motor
coordination and the reorganization of visual-motor
responses under conditions of sensory distortion (Hein and
Diamond, 1972? Held and Bossom, 1961; Held and Hein,
1963). Visual-motor rearrangement experiments have
typically been conducted on human adults and involve the
following paradigm: Subjects wear opthalmic prisms
which laterally displace the visual field and cause
33
errors in reaching toward visual targets. After such
errors have been noted, the subjects are prismatically
exposed to the visual environment under a variety of
conditions. . They are then retested for errors in reaching
or localizing visual targets. In time, with proper ex
posure conditions, the individuals adapt to the distorted
visual input. Reaching errors diminish and the subject
is able to perform coordinated visual-motor responses.
The degree to which adaptation occurs is highly
dependent upon the type of exposure to the visual en
vironment. Earlier it was shown that exposure of young
animals to the visual environment, while restrained from
self-produced movement, precludes proper development of
visual-motor functions (Held and Hein, 1963).
Similarly, exposure of prism-wearing adults to the
visual environment while restrained from self-produced
movement precludes a recoordination of visual-motor func
tion (Held and Hein, 1953). It appears that visual-
motor reorganization to prismatic distortion occurs best
if the subject is allowed bodily movement while pris
matically viewing the visual environment (Held and
Gottlieb, 1953; Held and Hein, 1953; Held and Schlank,
1959). Classic studies are cited below, but the
phenomenon of response-produced adaptation has been demon
strated in a large number of studies (Efstathiou, 1969;
3^
I-Iayrtal, 1971; Held and Freedman, 1963).
Held and Gottlieb (.195$) showed that errors in hand-
eye coordination caused by displacement of the retinal
image were reduced if the subject was able to prismat
ically view his moving hand. Previous explanations of
such decline in errors were in terms of trial, error and
correction learning. However, in the present experiment,
adaptation to the disarrangement of a spatial coordina
tion was obtained without providing the subject with
information about his errors. Adaptation occurred only
when the moving hand was viewed under the disarranged
condition.
Held and Hein (1958) investigated the significance
of movement-produced sensory stimulation in reducing
errors in prismatic hand-eye coordination. They used a
method of localization whereby an individual saw neither
his hand nor his markings aimed at a prismatically
visible target. The subject was thus unaware of his
errors. The subject was first required to make ten mark
ings at each intersection of four lines arranged in a
Tic-Tac-Toe framework. The pattern was laterally dis
placed. The subject's arm was then rested on a horizon
tal platform which pivoted at the elbow. He then re
ceived one of several three minute exposure conditions
during which he scanned his arm a) while it was immobile,
b) while he pivoted his arm through a 60 degree arc, or
c) while the arm was passively rotated through the arc by
the experimenter. The subject was tested on his ability
to mark the target points. Although the passive-movement
condition provided the eye with the same optical infor
mation that the active-movement condition did, what
proved to be the crucial connection between motor output
and visual feedback was lacking. The corrective shift
in localization (reduction of errors after exposure)
occurred only when the individual received reafferent
visual stimulation resulting from self-produced move
ments of a relevant body part.
Similar findings were obtained by Held and Schlank
(1958) using prismatic distortion in the distance dimen
sion. During the exposure conditions, the subject moved
his hand or the experimenter moved the subject's hand
while he viewed it as being at a greater distance op
tically than normal. Again, the reduction of errors of
localization of an object after self-produced are move
ments was great.
Held and Bossom (1961) believed that if adaptation
to prism-induced errors of hand-eye coordination required
self-produced movements of the hand and arm, compensation
for the errors of egocentric localization would probably
require movements of the entire body such as those which
occur during locomotion. Research was conducted to test
for compensation of egocentric localization following
brief exposure with passive movement compared with that
following equivalent exposure with self-produced move
ment. Subjects wore prisms which laterally displaced the
visual environment. During exposure conditions with the
prisms, subjects either walked about while viewing the
environment or viewed the same environment as they were
moved passively in a wheelchair. The measuring pro
cedure required the subject to orient himself to a slit
of light in an otherwise dark room. Measurements were
taken before and after the one hour exposure periods. As
usual, adaptation to the prisms was great in subjects
who walked through the environment. In contrast, adap
tation was poor in individuals exposed to the environ
ment while "restrained" in a wheelchair.
The above findings are in accord with those from
research on neonatal deprivation whereby animals re
strained while exposed to a visual environment do not
develop normal visual-motor function. The importance of
response-produced stimulation in adaptation to visual-
motor rearrangement is consistent with implications that
related processes underly- both the original development
of visual-motor function and its later adaptability to
rearrangement (Hein and Diamond, 1972} Held and Bossom,
37
1961; Held and Hein, 1963).
Discussed in the following section are a number of
studies which indicate that the capacity for visual-
motor recoordination may diminish with advancing age.
VISUAL-MOTOR REARRANGEMENT AND AGE
Sensory-motor rearrangement experiments of sorts
have been conducted with aged adults. The findings, in
general, point to a decline with advancing age in the
capacity to adapt to rearrangement of visual-motor coor
dinations. Although none of the following studies in
volve prismatic displacement of the visual environment,
all require the subject to recorrelate motor activity
with rearranged visual input.
In one of the earliest studies of this kind, Snoddy
(In Birren, 1959 > 595) tested subjects of various ages on
the ability to trace patterns while viewing them through
a mirror. Older subjects were found to be deficient in
this task. Similarly, Ruch (In Birren, 1959» 595) demon
strated a fall in the performance of older subjects on a
pursuit-rotor task when the target could be viewed only in
a mirror. The age-related impairment was much greater
than that found when the subjects were allowed direct
vision.
Szafran (In Welford, 195^, 129-133) had subjects of
ages varying from fifteen to sixty throw a small loop of
chain at a target five feet away. Three experimental
conditions were used; a) the subject could directly view
the target, b) the subject could directly view the target
but had to throw over a bar suspended thirty-two inches
above the floor, and c) the subject viewed the target in
a mirror and threw over an opaque screen thirty-two
inches high. In the latter condition, the target was
turned around 180 degrees so it could be viewed through
the mirror. The far and near dimension was thus reversed
and the target was seen at a place other than where the
subject directed his throw. Subjects did not differ in
performing the task under the first two conditions. In
contrast, older subjects showed significant impairment
in ability to hit the target when viewing it through the
mirror. Furthermore, they failed to compensate for
errors by either over or under-correcting successive
throws.
Older subjects also demonstrate impairments in
tracing reversed figures (Brown, in Welford, 1958, 70).
Individuals of advanced age treated the stimuli as normal
figures reversed and traced them as such. Younger sub
jects treated the stimuli as nonsense shapes and traced
them in whatever manner was convenient.
Impairments were exaggerated when the subjects are
required to write rather than trace the figures (Szafran,
in Welford, 1958, 136-139). Subjects in this series of
39
experiments were required to trace stimuli through a
mirror in which reversed figures looked normal and normal
figures looked reversed. They were also required to
write numbers and letters so that they appeared normal
in a mirror. Again, gross deficiencies in the perform
ance of these tasks were observed in the aged subjects.
An interesting finding which is related closely to
the prism experiments discussed earlier is that of
Szafran (In Welford, 1958» 139-1^0) regarding the use of
feedback by older individuals. Subjects ranging in age
from eighteen to sixty-nine were blindfolded and were
required to move their hand a distance of one foot side
ways and then to return to the starting position. Some
of the individuals received feedback as to the extent
of their errors. They were allowed to see the location
of their hand subsequent to performing the task. The
younger subjects benefited much more by the feedback
than did the older subjects. They appeared to translate
visual information into kinesthetic responses better than
did the aged subjects. When no feedback was given, sub
jects committed equal numbers of error.
Kay (195*1' t 1955) demonstrated further the inability
of aged subjects to perform translational experiments.
The subjects ranging in age from fifteen to seventy-two
were presented v/ith a set of twelve lights and twelve
corresponding keys. Individuals were required to press
a key each time its corresponding light was flashed on.
The light went off as soon as the key was pressed and
subsequently another light would go on. A series of such
trials was given per subject. Three conditions were
used; a) the lights were placed immediately above the
panel of keys, b) the lights were placed three feet away
from the panel of keys, and c) the lights were placed
three feet away and were turned through 180 degrees. The
results indicated no difference among the age groups on
the first condition, some slowing of the older subjects
on the second condition, and severe slowing of the older
subjects on the final condition.
Taken together, the data presented above indicate an
increasing deficit with increasing age in the ability to
recorrelate motor activity with rearranged visual input.
RELATIONS AMONG PROCESSES UNDERLYING
VISUAL-MOTOR DEVELOPMENT, VISUAL-MOTOR
ADAPTATION AND VISUAL-MOTOR RECOVERY OF FUNCTION
It has been shown earlier that amelioration of be
havioral deficits consequent to brain damage is induced
if damage occurs serially rather than simultaneously.
Thus, v/hen a structure represented bilaterally in the
brain is lesioned in two separate operations with a cer
tain number of days intervening between surgeries, other
areas of the brain seem to take over lost function. If
the same structure is removed bilaterally in a single
operation, the resulting behavioral deficits are more
severe and sometimes permanent. One of the factors
critical to the occurrence of recovery of visual function
is the interoperative experience that takes place between
two-stage removal of the visual cortex. It is clear that
visual deprivation during this period precludes the re
covery process and equates the effects of two-stage lesions
with those of single-stage cortical destruction (Meyer,
et al., 1958; Petrinovich and Bliss, 1966; Petrinovich and
Carew, 1969)* On the other hand, animals receiving various
types of visual stimulation during the interoperative per
iod recover visual capacity to varying degrees (Kircher,
et al.. 1970; Petrinovich and Carew, 1969).
The nature of the interoperative activity is the
subject of the present research. Exactly what types of
interoperative visual experience are required for com
plete recovery of visual function remains in question, but
some clues are provided in two parallel areas of research.
Evidence has been cited above that related processes
may underly both the original development of visual-motor
function and the reorganization of visual-motor function
under conditions of sensory distortion (Held and Bossom,
1961; Held and Diamond, 1972; Held and Hein, 1963).
One purpose of the present research was to investi
gate the possibility that the process of recovery of
42
visual function following two-stage ablation of the
striate cortex is related to the processes of development
and reorganization of visual-motor function. It was
hypothesized, therefore, that the occurrence and extent of
recovery of visual function is similarly dependent upon
self-produced movement during exposure to patterned visual
stimulation.
The first part of the experiment involved four
groups of young rats. The animals were tested for ability
to discriminate visual patterns, were given two-stage
lesions of the striate cortex, and were retested for
ability to discriminate visual patterns. Between two-
^tage surgeries, the subjects were exposed differentially
to visual stimulation four hours daily. The remaining
twenty hours were spent in total darkness.
The first group remained in total darkness during
the entire interoperative period. The second group was
exposed to diffused illumination during the four hour
daily exposure period. The third group was passively
transported through a patterned visual environment while
restrained in a holder. The fourth group was allowed un
restricted movement to a patterned visual environment
identical to that of the previous group. It was expected
that unrestrained animals exposed interoperatively to a
patterned visual environment would demonstrate the greatest
degree of recovery.
A second purpose of the present research was to
investigate age-related differences in the ability to
recover from two-stage ablations of the visual cortex.
Studies have been cited above which indicate progressive
deficits with advancing age in the ability to perform
tasks which require visual-motor recorrelations. In view
of the possibilities that the processes underlying visual-
motor reorganization may be related to the processes
underlying visual-motor recovery of function, and that
older subjects show deficits in the capacity for visual-
motor reorganization, it was expected that age-related
deficits exist in the capacity for two-stage recovery of
function. It was hypothesized that old animals would not
recover function to the same extent as young animals. The
second part of the proposed research involved groups of
rats, twenty-four months of age, which were run through
experimental procedures identical to those of groups
three and four. The aim of the study was to determine
whether recovery takes place in old animals to the same
extent and under the same conditions as with animals
three months of age.
CHAPTER II
METHODOLOGY
The study involved six groups of rats. Four groups
were composed of three month old animals and two were com
posed of twenty-four month old animals. Animals were
tested for ability to discriminate horizontal-vertical
patterns, were given two-stage ablations of the striate
cortex, and were retested for ability to discriminate
visual patterns. Between two-stage surgeries, the sub
jects were exposed differentially to visual stimulation
four hours daily. The remaining twenty hours were spent
in total darkness. The independent variables were Type of
Interoperative Stimulation and Age and the dependent
variable was Retention of the Pattern Discrimination Task.
Degree of retention was determined in terms of savings
scores on number of trials and number of errors committed
in reaching postoperative criterion.
The interoperative conditions and division of groups
were as follows:
GROUP I (100 days old): Animals were kept in the
dark for the eleven interoperative days.
GROUP II (100 days old): Animals were kept in
diffuse, unpatterned illumination for the eleven inter
operative days.
^5
GROUPS III (100 days old) and V (730 days old):
Animals were passively transported through a patterned
visual environment while restrained from movement.
GROUPS IV (100 days old) and VI (730 days old);
Animals were allowed unrestrained movement while exposed
to a patterned visual environment.
Histological examinations were done on all animals
following completion of the experiment to determine extent
and accuracy of lesions.
SUBJECTS
The subjects were sixty male Long-Evans, hooded
rats, sixteen of which were twenty-four months of age and
the rest of which were three months of age at time of
first testing. The older animals were obtained from the
vivarium of California State University at Long Beach.
The younger subjects were purchased from Charles Rivers
Laboratories of P/iassachusetts. The rats were housed in
the animal quarters of the Huntington Institute of Applied
Medical Research, Pasadena, California, where the experi
ment was conducted. All subjects were maintained with
ad libitum access to food and water.
APPARATUS
The apparatus was a modified Thompson-Bryant (1955)
visual discrimination chamber consisting of a start box,
choice compartment and illuminated goal box (Figure 1).
Figure 1. The two-choice visual discrimination
apparatus for testing ability to differentiate horizontal-
vertical discriminanda.
Animals were required to choose one of two doors leading
to the goal compartment, each door having different dis
crimination cues. The negative door (horizontal black-
white stripes) was locked and the positive door (vertical
black-white stripes) allowed the animal to avoid or es
cape shock by running into the goal box. The goal box
was illuminated by a 25 Watt bulb placed behind a diffu
sion panel. The position of the correct door was varied
randomly from right to left (Figure 2). When an animal
was placed in the start box, the experimenter lifted a
door v/hich activated a microswitch. After a ten second
delay, the switch initiated the onset of shock.
A scrambled constant current shock generator, de
signed and fabricated in-house, was used to deliver a lma
shock, of 2msec duration, three times per second (Figure
3).
PROCEDURE
Animals were trained to discriminate horizontal-
vertical patterns, v/ere given two-stage lesions of the
visual cortex, and were tested for postoperative retention
of the visual discrimination. Differential interoperative
experience was provided the various groups.
Pretraining: The animals underwent five days of pre-
training. During days one and two, the rats were taught
to run to the goal box to escape or avoid shock. Ten
Figure 2. Discrimination chamber showing discriminanda in right and left
positions.
Figure 3. Scrambled shock generator used to deliver
constant current pulses to the discrimination grid.
50
trials were given per day.
Over days three, four and five, two white trans
lucent doors were gradually lowered over the goal box
openings. The animals were trained to push through the
doors to enter the goal box. Ten trials were given per
day.
Discrimination Training: The task involved a horizontal-
vertical pattern discrimination. The stimuli included a
positive vertically striped door and a negative horizon
tally striped door. The stimuli v/ere switched according
to a random sequence obtained from a Hewlett-Packard 9810
calculator. The animal was allowed ten seconds to run
through the correct door before the grid was charged. A
response to the negative stimulus was always shocked.
Such a response involved the animal entering the wrong
alley by three or more inches. Animals v/ere tested pre
and postoperatively on the discrimination task. Pre
operative animals were discarded if they failed to reach
the nine/ten correct discrimination trials within twelve
days. Postoperative animals were run to an upper limit
of twenty days.
Recordings were made of the number of discrimination
trials to criteria and the number of discrimination errors
committed before learning the task.
Surgery: Surgery was performed under Nembutal anesthesia
(^Omg/kg IP), A scalp incision was made along the midline
of the head and subcutaneous tissue was deflected. The
area included in the bone flap was then marked with a
surgical felt pen. For removal of the visual cortex, a
triangular bone flap was made with the apex 2mm posterior
to Bregma. One side of the flap extended posteriorly and
somewhat tangentally to the temporal crest, The other
side ran parallel to the saggital suture, 2mm laterally.
The base ran parallel to the lamboidal suture lfmm
anteriorly to it. After removal of bone, the dura was
deflected and the exposed cortical tissue, now conforming
to the outline of Area 17, was removed by aspiration.
Lesions were performed in two stages with half the
animals of each group receiving left first-stage lesions
and half receiving right first-stage lesions. Eleven
interoperative days intervened between surgeries. Four
days after the second surgery, the second discrimination
session was begun.
Interooerative Experience;
a) Total Darkness: The first group of young
animals remained in absolute darkness during the inter
operative period. The area of housing was a small, quiet
room which was made light-tight. Extra food and water was
provided to preclude water bottle changes and addition of
food. Litter was changed once during which time inter
mittent light entered the room over a half-hour period.
b) Diffused li^ht; The second group of young
52
animals were placed four hours daily in a light diffusing
plastic cylinder, 6 inches in diameter and 2^ inches in
length (Figure >+). The cylinder was closed off at both
ends with sections of plastic diffusion panels. The
remaining twenty hours were spent in total darkness.
c) Patterned Vision with Motor Restriction; A
young and old group of rats were transported through a
patterned visual environment four hours daily while
restrained in a holder. The environment consisted of a
circular alley 6 2> / U - inches wide and 4 feet in outside
diameter (Figure 5)* The sides of the alley were white
in color. Visual stimuli were painted on the alleys with
black paint and included | wide striations placed in
various horizontal-vertical configurations (Figure 6).
Stimuli opposite each other along the alley were matched.
The restraining holders were of two sizes to accom
modate young and old animals and were made from metal cans
and metal grating (Figure 7). The end of the can had a
circular opening through which the animal's head could
protrude. The animal was held in position by a hairpin
loop of wire passed through the grating at the other end
of the holder.
The holders were attached to a rotating apparatus
turned by a variable speed motor. Animals were trans
ported through the environment at speeds ranging from one
revolution every one to five minutes. Speeds were random-
Figure k. Diffuse light chamber used with animals
exposed to diffused illumination.
Figure 5- Apparatus for transport of restrained
subjects through a patterned visual environment.
5^
M ill
Figure 6. Close-up of subject in place in
restraining holder.
Figure 7. Restraining holder for restriction of
motor movement.
ly changed every one-half hour during the exposure
period.
d) Patterned Vision with Unrestricted Movement;
A young and old group of rats were allowed free movement
in patterned visual alleys identical to those through
which animals in the previous condition were transported.
(Figure 8). The alley was partitioned into five
sections, and animals v/ere placed randomly into the
various sections on a daily basis. Alleys were covered
with :! inch screen.
Testing for Recovery; The animals were tested for
retention of the pattern discrimination postoperatively.
The procedure was identical to that used in the training
sessions. Retention scores were calculated using the
standard formula for per cent savings: The Original
Learning Score minus the relearning score divided by
the original learning score x 100). Savings
were determined for both trials and errors to criterion.
Autopsy: The animals were sacrificed with a lcc dosage
of Euthanasia. All old animals and four young animals
randomly selected from each group v/ere examined for
evidence of pathology of the major organ systems. All
aged subjects showed mild to moderate involvement of
the lungs in chronic respiratory disease, none were
hemorrhagic and emphysema was suspected in some cases.
Figure 8. a) Patterned visual environment
used with animals allowed free movement during
exposure periods.
h) The circular alley is
partitioned into units for individual animals.
CN
There was no indication of eye or nasal secretions in
these animals, Four of the aged rats had ulcerations
of the skin; three were in the Unrestrained group and
one was in the Restrained group. Crusty ulcerations of
the feet and tail were common to all animals. One
animal in the Restrained group appeared anemic. Of the
twenty young rats examined, four showed evidence of
chronic respiratory disease and one was indicated as
marginal. Two of these animals were in the Diffuse
group and two were in the Unrestrained group. The latter
animal belonged to the group kept interoperatively in
the dark. Another animal in the Dark group experienced
gastrointestinal infection including diarrhea prior to
sacrifice. This condition was not noted during testing
of the animal.
Histology: The brains of the animals were extracted
and fixed in 10 per cent buffered Formalin. One week
later, the tissues were sectioned and stained with
Hematoxylin-Eosin. Ten sections were taken every
millimeter through the occipital area of cortex.
Histological examinations revealed all lesions to
involve Visual Area 17, with mild to moderate involvement
of Areas 7 and 18. The corpus collasum was mildly
damaged in most cases. Figures 9a-f illustrate minimal
and maximal extents of damage performed in each group.
Statistical Analyses: Kruskal-Wallis and Mann-Whitney U
nonparametric statistics and a one-way analysis of
variance were the statistical analyses carried out with
the data.
59
Figures 9a-f. A comparison of minimal and
maximal■extents of cortical damage for each of the six
groups of animals.
©
Figure 9a. Group
Figure 9*>. Group II
Vi
Figure 9d.
d >
Group IV
Figure 9e Group V
Figure 9f Group VI
CHAPTER III
RESULTS
Lesion Size: For all groups, the mean percent age of
cortical destruction was 1^.6 per cent of the total neo
cortex. The extent of neocortical damage was evaluated
for each animal with the use of a planimeter. The surface
area of the bilateral lesions was divided by the total
surface area of the neocortex per animal. Converting
these values to percentages, the mean percentages of cor
tical destruction were computed for each group. These
means and corresponding standard deviations are shown in
Table 1. A one-way analysis of variance revealed no
differences among the groups in extent of cortical damage
(F = 0.86, df = 5/5^, p >.05, Table 2).
Preoperative Learning: Data for pre and postoperative
performance of all groups is summarized in Table 3. The
four groups of young animals were compared as to original
acquisition of the visual discrimination. As illustrated
in Table a Kuskal-Wallis Analysis of Variance revealed
no differences among groups in terms of trials (H = 0.82,
df = 3* P >.05) and errors to criterion (H = 0.76, df = 3>
p >.05). Thus, the young animals demonstrated good
capacity for pattern discrimination and were equivalent in
66
TABLE 1
KEAN PERCENTAGE OF CORTICAL DESTRUCTION
MEAN AND STANDARD DEVIATIONS
GROUP OF PERCENT CORTICAL DESTRUCTION
DARK 15.3 ± 1.27
DIFFUSE 14.7 + 1.75
RESTRAINED 14.3 ± 1.55
UNRESTRAINED 14.7 t 2.55
RESTRAINED-OLD 15.0 t 3.16
UNRESTRAINED-OLD 13.4 t 1.76
TABLE 2
ONE-WAY ANALYSIS OF VARIANCE
FOR EXTENT OF CORTICAL DAMAGE
SOURCE S3 df MS F P
TREATMENTS 20.03 5
4-. 01 0.86
> 0.05
ERROR
250.37
54- 4-. 64-
TOTALS 270.4-0
59
ON
CO
TABLE 3
MEDIAN LEARNING AND MEDIAN RETENTION SCORES
FOR YOUNG AND OLD ANIMALS
GROUP
PREOPERATIVE
N LEARNING
POSTOPERATIVE
RETENTION (£)
TRIALS ERRORS TRIALS ERRORS
(OL-IO) - (RL-10) ir100 OL-RL -
(OL-IO) XiUU OL A10°
DARK 10
85 37 -15^
-202
DIFFUSE 12 80
37 -171
-170
RESTRAINED 11 70 30 -171 -213
UNRESTRAINED 11 90
35
+130 + 20
RESTRAINED-OLD 8 60 26 -216
-255
UNRESTRAINED-OLD 8 50 22 - 50 - 62
Os
NO
TABLE k
KRUSKAL-Y/ALLIS ANALYSIS OF VARIANCE
FOR PREOPERATIVE LEARNING
OF YOUNG ANIMALS
GROUPS DARK DIFFUSE RESTRAINED UNRESTRAINED
R 2k2
2?^
216
259
TRIALS N 10 12 11 11
H=0.82 df=3
*d
V
•
0
Ul
R 239
296 228 22 7
ERRORS N 10 12 11 11
H=0.76 df=3
•d
V
•
0
O
71
ability to learn the task.
In contrast, a similar comparison between young and
old animals assigned to the Restrained and Unrestrained
conditions revealed young animals in acquisition of the
pattern discrimination (Table 3). Kuskal-Wallis evalu
ations of trials and errors to criterion revealed sig
nificant differences between age groups on errors commit
ted in reaching criterion (H = 8.1^, df = 3 * P <.02, Table:
5). No differences were demonstrated in terms of trials to;
criterion (H = 3.13, df = 3, p >.05). A subsequent Mann- :
Whitney U comparison of the old groups revealed no differ
ences in acquisition (U = 19, N1/N2 = 8/8, p >.05). Thus,:
both groups of two year old subjects committed signifi
cantly fewer errors in learning the discrimination than did:
i
three month old animals. It should be noted at this point
that five old animals were discarded from the experiment
because they failed to acquire the visual habit within
twelve days.
Postoperative Recovery: Following surgery, animals were
tested for sparing of the visual habit. Postoperative
discrimination ability was compared to preoperative
ability by means of savings scores for both trials to
criterion and number of discrimination errors committed
in reaching criterion. For trials to criterion, the
following computational formula was used:
TABLE 5
KRUSKAL-WALLIS ANALYSIS OF VARIANCE
FOR PREOPERATIVE LEARNING OF
YOUNG AND OLD, RESTRAINED
AND UNRESTRAINED GROUPS
GROUPS
RESTRAINED
YOUNG
UNRESTRAINED
YOUNG
RESTRAINED UNRESTRAINED
OlD OLD
R 222 2 56 160
99
TRIALS N 11 11 8 8
H=3.13 df=3 P > .05
R 2 54 261 142 84
ERRORS N 11 11 8 8
H=8.14 df=3 p < . 05*
(OL.-10) - (RL+-10)
------ _' - [ q--------: — X 100 = Pe^ cent savings of trials -to
criterion. For discrimination errors, the formula was
simply ^0I,e^ ~ ( ^ e) X 100 = per cent savings of discrim-
^oO
ination errors committed in reaching criterion. Retention
scores for trials and errors were computed for each group
of animals.
Comparisons of the postoperative retention scores
among the four groups of young animals indicated that
only those animals allowed unrestrained movement during
interoperative exposure to visual stimuli retained the
visual discrimination habit (Table 3). Virtually all
animals in the Dark, Diffuse and Restrained groups failed
to reach criterion on the visual task within the twenty-
day testing session. One animal in the Dark group reached
criterion on day 19, and two animals in the Restrained
condition reached criterion on days 11 and 13.
In contrast, all animals in the Unrestrained group
recovered the habit. Seven of the eleven animals in this
group demonstrated sparing, i.e. postoperative performance
v/as superior to preoperative performance.
As is shown in Table 6, the Unrestrained group of
animals v/as the only group showing recovery (H = 24.3»
df = 3» p <.001 for trials and errors). Thus, visual
deprivation during the interoperative period precludes
TABLE 6
KRUSKAL-WALLIS ANALYSIS OF VARIANCE
FOR POSTOPERATIVE RETENTION
OF YOUNG ANIMALS
GROUFS DARK DIFFUSE RESTRAINED UNRESTRAINED
R 27^ 3^5
30 5 67
TRIALS N 10 12 11 11
H=2^.3 df=3
P
<.001*
R 293
333
292
67
ERRORS N 10 12 11 11
H=2^.3
0^
I I
p
<.001*
75 1
two-stage recovery of visual function. Furthermore,
exposure to a patterned visual environment must be accom
panied by self-produced movement for recovery to occur.
A similar finding was made with the two year old
animals (Table 3). Older subjects allowed free movement
during interoperative exposure displayed recovery of
visual function. All animals in this group recovered the
task while three of the eight demonstrated sparing. Con
versely, all but one animal restrained during inter
operative exposure failed to reach criterion within the
twenty day testing session. The one exception reached
criterion on day 17. Mann-Whitney U comparisons were made
between the two groups and unrestrained animals were
found to be superior on both trials (U = 5* N1/N2 = 8/8,
p < ,001) and errors to criterion (U = 3» N1/N2 = 8/8,
p < .001).
Thus, for both young and old animals, exposure to a
patterned visual environment during the interoperative
period is insufficient to promote recovery of visual
function. Only those subjects allowed free movement in
the patterned visual environment displayed recovery.
Comparisons of young and old groups receiving patterned
vision, with or without movement, were also conducted.
No difference was found between young and old groups
restrained during interoperative exposure (Trials: U = *H,
Nl/fa2 = 8/11, p > .05; Errors: U = 33» N1/IM2 = 8/11,
p > .05). All but three animals failed to recover the
visual habit within the twenty day testing session.
There is an apparent age decrement in the ability
to recover vision under optimal exposure conditions, A
significant difference was found between young and old
animals in their postoperative performance. Old animals
were inferior to young animals both in terms of trials
(U = 22, N1/N2 = 8/11, p <.05) and errors to criterion
(U = 15, N1/N2 = 8/11, p <.01). Individual retention
scores for all groups are illustrated in Figures 10 and 11.
% RETENTION
+100
0
-100
-200
-300
-400
-500
3 5 6 1 2 4
GROUPS
Figure 10: individual retention scores for trials
to criterion for all groups.
% RETENTION
+100
0
-100
-200
-300
-400
-500
1 2 3 4 5 6
GROUPS
Figure 11: Individual retention scores for errors
to criterion for all groups. : J D
CHAPTER IV
DISCUSSION
The data clearly indicate that visual deprivation
during the interoperative period between two-stage lesions
of the striate cortex precludes the recovery of visual-
motor function. Both interoperative exposure to absolute
darkness and exposure to diffused.light were insufficient
for the occurrence of functional recovery. Of even
greater significance is the fact that self-produced move
ment must accompany interoperative exposure to a patterned
visual environment for recovery to occur. Animals re
strained from movement during such exposure failed to
demonstrate sparing of visual discrimination abilities.
These findings are in accord with data from two
related areas of research; neonatal visual deprivation
studies and- visual-motor rearrangement experiments. Self
produced movement must accompany exposure to the visual
environment for normal development of visual-motor
function (Fish and Robinson, 1971; Held and Hein, 1963;
Meyers, 196^; Riesen, 1965; Riesen and Aarons, 1959)*
Similarly, self-produced movement must accompany pris
matic exposure to the visual environment for optimal
79
80
adaptation to prismatically rearranged visual input
(Held and Gottlieb, 1958; Held and Hein, 1958. Held and
Schlank, 1959). The similarity in findings suggests that
related processes underly visual-motor development,
visual-motor adaptation and visual-motor recovery.
Data from this experiment also suggest age-related
changes in the capacity for postoperative functional re
covery. There appears to be a significant reduction in
the capacity to recover function under optimal exposure
conditions with advanced age. Old animals allowed un
restrained movement during interoperative exposure to
patterned stimuli demonstrated a level of visual recovery
inferior to that of young adult animals. This finding was
expected since there is evidence of age decrements in
adaptive capacity and since there exists the possibility
that related processes underly visual-motor adaptation
and visual-motor recovery (Brown, In Welford, 1958, 70;
Kay, 195^ and 1955; Szafran, In Birren, 1959» 595).
More detailed discussion of the results is presented
below.
Influences of Interoperative Experience on Recovery
Data from this research indicate that one of the
most significant determinants of the occurrence of two-
stage recovery of function is the nature of sensory
stimulation that occurs during the interoperative period.
81
Previous experiments indicated that at least nonspecific
sensory stimulation was required between ablations of the
visual cortex for the sparing of preoperatively learned
visual habits (Petrinovich and Bliss, 1966; Petrinovich
and Carew, 1969; Stewart and Ades, 1951? Thompson, i960).
All these experiments, however, utilized black-white
visual discriminations which can be acquired with or
without an intact visual cortex (Bland and Cooper, 1970;
Horel, 1968; Spear and Braun, 1969). The mediation of the
task is therefore related to several visual areas of the
brain including cortical and subcortical regions.
In the present experiment, a horizontal-vertical
pattern discrimination was employed. The capacity to
differentiate visual patterns has been reliably associated
with function of the visual cortex. Ablation of this
cortical region results in the abolishment of pattern
discrimination (Bauer and Hughes, 1970; Horel et al. .
1966; Thompson, 1969). Thus, the occurrence of recovery
of pattern vision following sequential removal of visual
cortex is probably a consequence of the functional and
perhaps physical reorganization of areas not primarily
responsible for this visual capacity. Furthermore,
because it was desired to relate findings on recovery to
findings from neonatal deprivation studies, use of a
pattern discrimination habit was necessary. Deprivation
experiments have repeatedly demonstrated that intensity
discriminations develop under endogenous control and are
not susceptible to disruption by early manipulation of
visual experience (Riesen, 1973)*
Results of this experiment remain in accord with
those studies of recovery utilizing intensity discrimina
tion (Meyer et al.. 1958; Petrinovich and Bliss, 1966;
Petrinovich and Carew, 1969). Interoperative visual
deprivation precludes two-stage recovery of visual
function. Animals kept in the dark during the eleven
day interoperative interval failed to retain the pattern
discrimination and furthermore, with one exception, were
unable to relearn the task within the twenty day post
operative testing session. One animal in this group did
relearn the pattern discrimination after 180 trials and
was found to have a lesion size of 10.3 per cent of the
neocortex. The possibility exists that, in this subject,
insufficient removal of the visual cortex was responsible
for postoperative recovery. Petrinovich and Bliss (1966)
and Petrinovich and Carew (1969) demonstrated that lesion
size was important to the occurrence of visual recovery.
Small lesions required less specific interoperative ac
tivity than did large lesions.
To further relate the present research to research
in neonatal deprivation, a second group of animals was
83
exposed daily to diffuse light between the two-stage re
movals of the visual cortex. Exposure to diffuse light
during early perceptual development precludes proper
development of visual-motor function (Riesen, 1973)*
Similarly, it was found that exposure to diffuse light
during the interoperative period precluded two-stage re
covery of the pattern discrimination. The habit was never
regained during the twenty day postoperative testing
session.
Of great significance is the finding that animals
passively transported through a patterned visual environ
ment between surgeries failed to demonstrate postoperative
retention of the pattern discrimination. In time, two of
these eleven animals were able to relearn the discrimina
tion requiring 110 and 130 trials to reach criterion.
Thus, exposure to patterned visual discrimination may
promote some degree of visual recovery but is insufficient
for sparing of the habit. Four young animals in this
group were run for twenty-five days postoperatively and
still failed to relearn the discrimination.
The possibility that emotional factors may have
played a role in postoperative performance is acknowl
edged. However, the possibility is considered remote
since the subjects failed to show evidence of emotionality
subsequent to the second interoperative day. Furthermore,
Sk
the degree of motor restriction allowed for head move
ments and body shifts. Many types of restraints were
fabricated prior to the beginning of the experiment and
the present equipment was found to be conducive to low
levels of emotionality. Subsequent to the second lesion,
these subjects were not found to exhibit increased arousal
upon handling relative to animals in the other groups.
In contrast to animals in the Restrained condition,
all animals allowed free movement during interoperative
exposure to patterned stimuli recovered the discrimina
tion habit. In fact, seven of these animals demonstrated
sparing; that is, their postoperative performance sur
passed their preoperative performance.
There is thus clear evidence that the occurrence of
two-stage recovery of visual function is dependent upon
the occurrence of visual-motor experience during the in
teroperative period. Visual experience alone, including
exposure to patterns used in the actual discrimination,
is not sufficient for the sparing of visual function.
Practical implications of these results involve consider
ation of exposure conditions necessary for visual-motor
rehabilitation subsequent to brain damage. Studies are
warranted to determine the significance of self-produced
movement to therapeutic procedures employed consequent to
brain trauma. Theoretical implications of these results
8 5
involve consideration of the processes underlying visual-
motor development and visual-motor adaptation. Results
of this study clearly indicate that self-produced move
ment during exposure to a patterned visual environment is :
fundamental to the recovery process underlying return of
visual-motor function. There is thus significant impli
cation that underlying mechanisms of visual-motor
recovery, adaptation and development are related.
Influence of Age on Recovery
Results of this experiment indicate that there is a
deficit with advanced age in the ability to recover visual;
function following two-stage lesions of the striate cor
tex. Under optimal interoperative conditions allowing
free movement during exposure to a patterned environment,
the two year old animals demonstrated a level of recovery ;
inferior to that of the young adult rats. Both old and
young animals were equivalent in failure to recover the
pattern discrimination after being restrained during ex
posure to the patterned environment. Again, as with the
Restrained group of young animals, one of the old animals
was able to relearn the task after 170 trials. None of
the old rats showed sparing in the Restrained condition,
while three demonstrated sparing in the Unrestrained
condition,
Thus, although self-produced movement v/as significant
•bo the recovery of both young and old animals, the extent
of recovery was greater in the young subjects. There
appears then, to be a decrement with advanced age in the
ability to recover'visual function even under optimal
conditions following two-stage lesions of the striate
cortex. The possibility exists that the inferior re
covery of the aged animals v/as due to a generalized
physical dysfunction postoperatively rather than to a
difference in neurological reorganization. Old animals
regained consciousness, following surgery, more slowly
than did young animals. They also appeared sluggish for
longer periods of time postsurgically. In addition, all
were found at autopsy to be suffering from chronic
respiratory infection. Although this condition is prac
tically universal among rats this age, its effect upon
general recovery cannot be ignored. Nonetheless, the old
animals did appear in good health during postoperative
testing and running latencies were not affected post
surgically. Future investigations should include animals
of intermediate age in which physical pathologies may be
less common.
The age decrement in recovery is congruent with
findings from sensory-motor rearrangement experiments on
aged human adults. In studies which required the subject
to recorrelate motor activity with rearranged visual
input, age-related decrements in sensory-motor adaptation
were found (Brown, In Weiford, 195”• 70; Kay, 195^* 1955;
Szafran, In Birren, 1959» 595)• Results of the present
experiment indicate that related processes underly both
visual-motor adaptation and visual-motor recovery. Thus,
the present findings that age-related decrements exist
in recovery of visual-motor function are consistent with
previous findings that visual-motor reorganization
abilities diminish with age.
As was mentioned in the previous chapter, the two
groups of old animals were found to be superior to the
young animals in preoperative acquisition of the pattern
discrimination. Whether or not this age effect is a real
phenomenon remains in question since five old animals had
to be eliminated from the experiment. They failed to
learn the visual task within twelve days. l \ ' o elimination
of subjects was required for young animals. Nonetheless,
the effects, if any, of advanced age on acquisition of the
two-choice pattern discrimination are not entirely clear
and warrant further investigation.
Physical Correlates of Functional Reorganization
Perhaps the most appropriate subject for future
investigations is the correlation between functional
recovery and physical changes known to follow brain
lesions. Such changes include collateral sprouting of
88
neurons which remain intact postsurgically and the for
mation of anomalous reinnervations. Deafferented areas
are often found to be reinnervated by processes with
which they are not normally connected.
In rats, electrolytic destruction of the substantia
nigra and part of the ventromedial midbrain tegmentum led
to regenerative sprouting of axons from catecholamine
mesencephalic neurons (Katzman, et al. , 1971). Initial
accumulation of catecholamine in areas surrounding the
lesion was noted three days postoperatively. Sprouting
progressed for one to seven weeks after neural destruc
tion.
Similarly, a section through the medial lemniscus of
the rat was found eighteen days later to be recrossed by
axons which selectively regenerated around the cut
(Marks, 1972).
Raisman (1969) studies the physical consequences of
lesions placed in two fiber pathways leading to the sep
tum. Hippocampal fibers normally pass to the septum via
the fimbria and terminate primarily on dendrites of the
septal neurons. Fibers from the hypothalamus arrive via
the medial forebrain bundle (MFB) and terminate both on
dendrites and on cell somata. Lesions of the hippocampal
pathway were found to produce unusually high proportions
of axon terminals contacting dendritic spires. This
finding suggested abnormal reinnervation by remaining
terminals. Lesions of the MFB resulted in a high pro
portion of fimbrial fibers now terminating on axosomatic
sites. These sites are not normally occupied by fimbrial
fibers. Changes occurred over three to six months.
Deafferentation was said to act as a stimulus for re
innervation such that the original constraints preventing
hippocampal fibers from terminating at axosomatic sites
were lost. This loss of specificity was thought to
underly the process of functional recovery.
Fimbrial lesions were also found to cause a marked
increase in the adrenergic innervation of the septal
nuclei that normally receive hippocampal projections
(Moore et al.. 1971). These changes occurred between
eight and fifteen days postoperatively and progressed over
a period of three months. The increased norepinephrine
levels were related to formation of new terminals
sprouting from neighboring axons.
Studies have also been conducted on the hippocampus
of the rat after deafferentation by lesions of the
entorhinal cortex (Lynch et al.. 1972). Entorhinal
fibers normally terminate in the outer molecular layer of
the dentate gyrus. Thirty to forty days postoperatively,
an intense band of acetylcholinesterase was found in this
layer. Subsequent lesions of the septum eliminated the
90
AChS band, thus suggesting that septal terminals sprouted
and innervated the deafferented regions of the hippo
campus .
In a subsequent study, lesions of the entorhinal
cortex led to the spread of commissural projections from
their normal location in the inner molecular layer to the
deafferented areas of the outer molecular layer (Lynch
et al., 1973)* Stimulation of the commissure evoked
short-latency responses in the outer molecular layer
where they are not normally found. Thus, there is strong
evidence that postlesion axonal sprouting leads to the
formation of permanent functional connections.
Relevant to the present research are studies in
volving axonal sprouting subsequent to destruction of
the visual cortex. Sprouting of the visual pathways has
been reported in the hamster (Schneider, 1970) and rabbit
(Ralston and Chow, 1973). Removal of the occipital cortex
of the rat has been found to result in sprouting of the
optic tract (Goodman and Morel, 1966). Sprouting
occurred only at two loci, the caudal half of the ventral
lateral geniculate nucleus, pars lateralis and the caudal
portion of the lateral nucleus of the optic tract and its
subadjacent medial quarter of pretectal nucleus. These
regions are major areas of convergence of retinofugal and
occipitofugal pathways. No other deafferented regions
91
demonstrated sprouting.
Many of these researchers believe that the abnormal
connections that form after brain damage play a crucial
role in recovery of function. Future investigations are
warranted to determine if sprouting of the optic tract
occurs in animals which demonstrate recovery of visual
function and does not occur in animals which fail to
recover. Whatever physiological changes accompany the
recovery process, it is clear from the present research
that specific sensory stimulation is required for the
process to be initiated.
CONCLUSIONS AND IMPLICATIONS
1) Recovery of visual function following two-stage
lesions of the striate cortex is dependent upon the
occurrence of interoperative visual-motor experience.
Interoperative visual deprivation including exposure to
darkness or diffuse illumination precludes the occurrence
of visual recovery. Furthermore, visual stimulation
alone is not sufficient for restoration of function.
Passive transport through a patterned environment with
restriction of motor movement failed to promote recovery.
Self-produced movement must accompany interoperative ex
posure. It now appears that, for specific types of
neurological damage, very specific forms of sensory
stimulation must be incorporated during rehabilitation.
92
The data indicate that the initiation of physiological
changes underlying visual-motor reorganization is de
pendent upon highly specific types of sensory stimulation.
2) The importance of self-produced movement to the
occurrence of visual recovery is congruent with findings
from two related areas of research; neonatal visual
deprivation studies and visual-motor rearrangement ex
periments. The results of the present study indicate
that related processes underly visual-motor development,
visual-motor adaptation and visual-motor recovery. Thus,
functional plasticity of the visual system is dependent
upon contiguous visual-motor experience.
3) From the present data, there are implications
that functional plasticity within the central nervous
system diminishes with age. Under ideal exposure con
ditions, two year old animals were inferior to young
adult animals in recovering visual function.
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93
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Dru, Denise
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Influences Of Interoperative Experience And Age On Recovery Of Visual Function Following Two-Stage Lesions Of The Striate Cortex
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