Smart prosthetics: teaching the body with technology

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SMART PROSTHETICS:
TEACHING THE BODY WITH TECHNOLOGY

by

Haley S. Poland

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF ARTS
(PRINT JOURNALISM)

May 2007

Copyright 2007 Haley S. Poland
ii

ACKNOWLEDGEMENTS

Many thanks to my committee members
K.C. Cole, Jon Kotler, and Félix Gutiérrez;
Special thanks to Dr. Gerald Loeb for his technical expertise.
iii
TABLE OF CONTENTS

Acknowledgements………………………………………………….ii
Abstract……………………………………………………………...iv
Main Body…………………………………………………………...1
Bibliography…………………………………………………………25

iv
ABSTRACT

In recent years, neuroscientists and biomedical engineers together have made
great strides in patching once-impassible gaps in the nervous system’s electrical
matrix with neural prostheses. Cutting-edge neural or “smart” prostheses are nothing
like the past generation of prostheses, which sit mute and lifeless next to the body’s
natural systems. Smart prostheses actually speak the electrical language of the body,
and can help train or retrain the nervous system by taking advantage of the
neuroplasticity of the brain and nervous system. The human body can integrate
neuroprosthetic technology to enable remarkable recovery from deafness, blindness,
and paralysis, among other conditions. This article discusses the cochlear implant,
retinal implant, functional electrical stimulation devices and the cortical implant
known as BrainGate. Rather than feeling more machine-like as they integrate their
bodies with technology, neural prosthesis users often describe feeling more human
and more confident of their place in the human world.
1
The human brain weighs about the same as a ripe cantaloupe. If you hold one
in your hands, you have before you the encyclopedia of an entire life. Everything
that person had ever said or done or felt or feared is written in that three-pound mass
in the intricate language of neurons. By itself, of course, the brain is cold, bumpy,
silent. For without the body’s electrical communication system—without the
corporeal currents that enable life—the magic is lost. The weight of the book
remains, but the words have no meaning.
The human body is a biological power grid with the brain as the control
station. It thrums with electrical activity. Electrical signals course, in every
direction, in millions of overlapped and intertwined conduits. Encoded in those
minute electrical pulses—the mortal Morse code—are messages either to or from the
brain. When you reach for someone’s hand, every step of the process involves a
deluge of electrical information. Your hand reaches out because signals shoot from
your brain telling your hand to do so. As it moves through space, your brain knows
the location of each finger, even with your eyes closed, because stretch receptors in
the muscles transmit status reports. When you touch the other person’s hand,
receptors on the skin’s surface send electrical information back to the brain
conveying its texture, temperature, tremor.
In the able-bodied, the electrical systems work quietly in concert, a process
mundane yet miraculous. But for millions of others, disruptions in the biological
power grid mean severe disability and a pronounced inability to live and
communicate normally. If the inner ear cannot turn sound waves into electrical
2
signals, then the auditory cortex has nothing to translate and the person is deaf.
Similarly, if the eye loses its ability to detect and comprehend light, the visual cortex
sits idle and the person is blind. In sensory disorders such as these, the receptors that
link a person to the world stop sending bulletins to the brain. The neural wires
running from the ears or eyes can often still carry currents of electrical information.
But with no coherent messages to transmit, there is just static; the brain waits to
translate code that never comes.
In movement disorders and paralysis, the circumstances are reversed. It is
the body that waits. When a person suffers a stroke, part of the motor cortex (the
section of the brain that controls movement) is damaged, rendered unable to send
signals. With no input, the motors in a particular neighborhood of the body stop
running; the arm hangs limp at the stroke patient’s side. If the spinal cord is injured,
the main power line is severed, which can cause either partial or total paralysis.
Electrical signals may course vigorously from the brain with a message to move the
arms or legs, but they rush to a dead end. The main bridge is out so the message
never makes it to its destination.
In recent years, neuroscientists and biomedical engineers together have made
great strides in patching these once-impassible gaps in the nervous system matrix
with neural prostheses. A prosthesis is an artificial body part that helps where some
function is lost or impaired, including anything from false teeth to aid in chewing to
artificial joints to aid in walking. Cutting-edge neural or “smart” prostheses are
nothing like the past generation of prostheses, which sit mute and lifeless next to the
3
body’s natural systems (a la Captain Hook). Smart prostheses actually speak the
electrical language of the body.
The term “smart” implies that a prosthetic device can think for itself, act on
its own. And to some extent, neural prostheses can. They have their own little
“brains” in the form of microscale computer chips which generate electrical signals
loosely resembling natural ones; stimulators transmit that information to either the
brain or body. The devices operate where the body’s circuitry is disrupted—where
the person has a deficit—to help restore function, be it hearing, movement, or sight.
Implants minute and resilient enough to be nestled in the inner ear, the eye, the
muscles, or elsewhere can either bypass or replace the body’s faulty wiring to enable
remarkable recovery.
But even more astonishing, “smart” means able to capitalize upon—even
propel—the natural processes of the brain and body. In the Oxford American
dictionary, “plastic” is defined as “easily shaped or molded,” and also as “offering
scope for creativity.” Neuroplasticity is the ability of the creative brain and nervous
system to expand and reorganize with every experience and obstacle. Every second
of our lives, neurons- those excitable little cells that make up the brain, spinal cord,
and peripheral nerves- are changing in response to whatever is going on in the
neighborhood of the body for which they’re responsible. Among other things, they
can modify how they communicate with other neurons or sprout some new
branchlike dendrites to receive and transfer more information. Even an elderly brain
4
is far from “hard-wired.” Regardless of your age, the brain you will have when you
finish this article is physically different than the one you started with.
Little more than fifty years ago, most scientists agreed that learning and
memory created small physiological changes throughout life. However, the majority
held that the regional “map” of the brain could not be altered after the first few years
of life. Scientists had no idea the extent to which the brain could reorganize, much
less reorganize with the help of manmade prosthetic devices. However in the 1970s,
extensive experimentation with monkeys began to reveal that the brain, in particular
the cortex, had a stunning capacity for change. In fact, neuroscientists demonstrated
that if part of a monkey’s cortex stopped receiving signals from the body (for
example, if the nerve for a certain part of the hand was severed), the cortex would
restructure itself to make use of that now idle brain territory. The same has proven
true in humans. Smart prostheses, by taking advantage of this plasticity and by
speaking the electrical language of the body, help people with disabilities coax their
brains and nervous systems to adapt.
“The computer invaded the sacred domain of my body yet to my own
astonishment we learned to work together as a total system, mutually changing each
other in the process,” reflected Michael Chorost, who had his hearing restored by a
cochlear implant. “I fed it lithium-ion batteries; it fed me electrons. I altered its
software; it repatterned the dendrites in my auditory cortex. We have literally
reprogrammed each other.”
5
What’s more, neural prostheses teach scientists volumes about how the brain
works, how the nervous system heals itself. Each device opens wide a new window
into the creative brain that would have remained shut otherwise. “It’s an opportunity
to test theories of the mind which we love to promulgate but can’t test any other
way,” said Gerald Loeb, professor of biomedical engineering at the University of
Southern California and one of the original innovators of neural interfaces.
In the past decade, a concept that has stuffed the pages of sci-fi novels for a
century became real: the human body integrated machinery. Not only can neural
prostheses speak the electrical language of the body, but the brain and nervous
system can learn from them, use them as tools, enlist them to self- heal. Smart
prosthetic technology encourages the nervous system to lay down new neural wiring,
helpfully nudging adaptive processes that occur naturally.
Unquestionably the most successful neural interface to date, the cochlear
implant has been restoring hearing to the deaf since the early 1980s. Loeb, one of its
primary developers, said the biggest surprise was discovering how the plastic brain
can make the most of relatively crude input. Neural prostheses that feed information
into the sensory nervous system, such as the cochlear implant, may speak the
electrical language of the body and brain, but the conversation is necessarily
rudimentary, like baby talk. Technology cannot introduce anything close to the
sensory information the brain receives naturally, in part because the information is
too complicated and in part because neural interfaces cannot replicate the highly-
evolved sense organs for which they substitute.
6
Consider, for example, the complex system of hearing: the outer ear (the
visible part) funnels sound waves from the environment into the ear canal, where the
sound waves cause the eardrum to vibrate. When the eardrum vibrates, so does a
chain of tiny bones in the cavity behind it. The infinitesimal motion of those bones
generates wavelets in the fluid-filled, snail-shaped cochlea of the inner ear.
Thousands of supersensitive microscopic hair cells sway in the fluid like arm hair in
the bathtub. With each tiny movement, chemical neurotransmitters are released and
then detected by nerves running to the brain. In essence, hair cells report to the
neurons which report to the brain that the dog is barking, the phone is ringing, and
the baby is crying.
Deafness, in the vast majority of cases, is caused by damaged or
degenerative cochlear hair cells. Sound waves enter the ear but are useless without
hair cells to detect them, like radio waves traveling through a room without a radio
receiver. When hair cells cease translating sound waves into electrical signals, the
inner ear’s 30,000 nerve fibers have nothing to do, no messages to transmit to the
brain.
This is where the cochlear implant comes in. By directly stimulating the
neurons of the inner ear, the device bypasses the inoperative anatomy. With just
sixteen electrodes for those thousands of nerve fibers, it delivers miniscule electrical
impulses that represent a “dumbed-down” version of normal sound. “It’s akin to
playing Chopin with your forearms,” says Dr. Michael Merzenich, a neuroplasticity
7
research pioneer and professor of Otolaryngology at the Keck Center for Integrative
Neurosciences at the University of California San Francisco.
While it may not compete with the machinery of Mother Nature, the cochlear
implant is no slouch when it comes to complexity. A small microphone, which can
be worn either on the shirt or in front of the ear, captures sound from the
surroundings and software programmed into a microcomputer simplifies the sound.
The processor deletes everything deemed too loud (and therefore potentially
harmful), as well as partitions the entire spectrum of audible frequencies into just 16
channels, one corresponding to each tiny electrode. The electrodes, embedded in a
silicon thread less than a millimeter wide, directly stimulate the auditory nerve fibers
of the inner ear, allowing the nerves to get back to work transmitting electrical
signals to the brain. The signals may not come from the hair cells—their natural
source—but the brain doesn’t care. Coded messages are coming in and the plastic
brain starts trying its hardest to decode them.
Not long ago, Michael Chorost couldn’t have heard a symbol crash a foot
away, much less a person speaking. Since birth, he had lived with extremely poor
hearing, the result of his mother’s bout with rubella while pregnant. He wore
hearing aids on both ears throughout his life; by effectively screaming the sound at
his few and mangled hair cells, they allowed him to live relatively normally. Then
six years ago at age 36, for reasons unknown, the last of his hair cells gave up. The
world went from quiet to silent.
8
Today, an observer might think Chorost still has a hearing aid, because that’s
essentially what a cochlear implant looks like—except that a wire runs from the
flesh-colored box hanging on his ear to a disk on his skull just behind it. The part of
the device that looks like a hearing aid is the computer processor, which simplifies
sound. That simplified electrical input runs through the small cord to a transmitter: a
disk the diameter of a quarter that magnetically adheres to Chorost’s head behind his
ear. The information then whizzes through the skin on a radio wave to a receiver
tucked carefully by a surgeon into a well drilled in his skull, just under the skin.
Where the implanted part of the device is embedded, a flat bulge, imperceptible
except by touch, slightly elevates the thin flesh of his scalp, like a book under a
blanket. From that implanted receiver runs a long wire to the electrode array
threaded deep into the cochlea of Chorost’s inner ear.
Chorost’s cochlear implant brought him back to the world of sound, but it
wasn’t the world he’d known with his hearing aids. Nothing sounded as it had.
Nothing even made sense. His brain had been used to complex signals representing
the world of natural sound, but the cochlear implant transmitted only baby talk.
“What do you want for breakfast?” sounded like, “zzzzz szz szvizzz ur brfzzzzzz?”
The first time Chorost took a hearing test, he scored 17%, which he says was
humiliating. But three years later, he scored 70%. And today, thanks to
neuroplasticity, he can hear the air vent whirring above him. In his book Rebuilt: My
Journey Back to the Hearing World, he likens relearning hearing to looking at a
Magic Eye poster. “You stare at a featureless blur for awhile. Little parts of the
9
image start to come in to focus here and there, teasing you. Then whoom, it’s all
there and you can see what it is.”
Over several months, Chorost’s brain—he calls it a pattern-matching
machine—restyled its neuronal fabric to make sense of a peculiar and paltry input.
During the first few weeks, he helped his brain to make the connections by reading
aloud, pairing the foreign sounds coming out of his mouth with the visual input of
the familiar words on the page. “So that’s what an ‘r’ sounds like now,” he recalls
thinking, as he recited children’s books. Chorost also spent hours with the
audiologists as they together “mapped” his cochlea, testing which frequencies of
sound best corresponded to which electrodes. Today’s patients don’t have to go
through so much; more advanced data processing, more accurate cochlear mapping,
and a better understanding of what input best serves the brain’s neuroplasticity
means that most patients are functional right out of the box. More than 100,000
people to date have come back to the hearing world using cochlear implants. “The
body is just a tool that the brain already knows how to use,” said Chorost. “Giving
someone a cochlear implant is giving the person a tool that they can learn to use to
heal themselves.”
Twenty-five years of general use has demonstrated to scientists how the brain
can learn to process artificial sound with a cochlear implant. The ear is a relatively
simple system because it deals only with sound frequencies, which are tonotopically
arranged in the cochlea. (Scientists know which regions detect the highs and the
lows.) On the other hand, the eye—the most highly-developed sensory organ—deals
10
with spatial relationships, brightness, motion, and color, all of which are represented
by elaborately intertwined neural circuitry. Vision employs more than 30 percent of
the brain’s total volume, with dedicated regions located all over the brain. Even so,
scientists have made remarkable progress in using technology to substitute for the
circuitry of sight.
Beginning in 2002, six people—one who had been blind for fifty years—saw
again using retinal implants. The developers of the first retinal prosthesis took
wonderful advantage of the years of research that went into the cochlear implant:
they used the same processor to simplify and transmit the signals. What differed was
the input. Instead of using a microphone to gather information, the scientists hooked
it up to a camera. Instead of simplifying frequencies of sound, it simplified patterns
of light.
In normal vision, an image of the outside world is focused onto a light-
sensitive membrane at the back of the eye called the retina. Photoreceptors in the
retina—rods and cones—absorb and code the constantly changing patterns of light
into neuronal signals, or electrical messages for the brain. Both retinitis pigmentosa
(RP) and age-related macular degeneration (AMD) are diseases in which the light-
sensing rods and cones of the retina degenerate and disappear. About one in every
4,000 people is born with retinitis pigmentosa, an inherited condition. As the
photoreceptors die off over the decades, poor night vision progresses to tunnel vision
and eventually to blindness. In age-related macular degeneration, central vision
11
deteriorates, sometimes rapidly. More than 25 million people, including 6 million in
the United States, are blind or nearly blind from these diseases.
Though people with RP and AMD lose their rods and cones, often the retinal
neurons are preserved to a great extent. So, much like a cochlear implant, the retinal
implant bypasses the ruined receptors (rods and cones) and directly stimulates the
related neurons. It circumvents the damage—the flaw in the electrical pathway—and
delivers a simplified message directly to the nerves.
The retinal prosthesis makes use of a tiny camera, concealed either in the
nose bridge or behind the tinted glass frame of a pair of sunglasses, to videotape the
patient’s surroundings with the resolution of an average digital camera (4
megapixels). The processor drastically simplifies whatever the camera is “seeing” by
reducing normal vision’s 256 gray scales (levels of brightness) to ten. Neither color
nor details remain. The visual information then travels by radio wave to an
implanted receiver, which stimulates an electrode array. Whereas the cochlear
electrode array rests amongst the gnarled, motionless hair cells of a deaf person’s
inner ear, the retinal electrode array is pinned to the rodless, coneless surface of a
blind person’s retina with a tack the size of a human hair.
Just like the cochlear implant, the first version of the retinal implant used 16
electrodes. But whereas the healthy cochlea has 30,000 nerve fibers sending sensory
information to the brain, the eye has 1.2 million. That’s 16 electrodes for 1.2 million
fibers. When the scientists tested the very first patient, they didn’t expect much
according to Mark Humayun, professor of ophthalmology at the Doheny Eye
12
Institute at the University of Southern California. (Humayun is an innovator of the
retinal prosthesis and also performed all six implantation surgeries.) “We really
thought they would just see black and white, maybe a little gray scale, maybe a little
movement,” he said, with bewilderment in his voice to this day. “But there’s no way
you should be able to use 16 pixels to differentiate a plate from a cup. That’s just
staggering.”
Granted, the plate was a “saucer” of light (and a knife was described as a
“runway”) but the patients could decipher white shapes against a black background.
Anecdotal evidence showed marked improvement over time, indicating that the brain
reorganizes around its new reality. Whereas cochlear implant users taught the brain
by reading aloud and matching the foreign sounds they heard with the familiar words
on the page, retinal implant users learned by touching the objects and matching the
abstract shapes they saw with what they felt with their hands. The patients became
increasingly confident in identifying the objects without having to touch them. “First
it was a guess, then a pretty good guess, then it wasn’t a guess,” said Humayun.
“They knew.”
In March 2007, Humayun announced that the Food and Drug Administration
(FDA) approved a clinical study to implant 50 to 75 blind people with the second
generation of retinal implants. Named for the Greek mythological creature of 100
eyes, the Argus II, developed by USC and Second Sights Medical Products, has 60
electrodes and is a quarter the size of the Model One. If things go as anticipated in
the clinical trial, the Argus II could become available to the public in just a few
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years. “Before we never would have thought to commercialize a 60-pixel device,”
said Humayun. “But when we saw what we could do with 16…that’s a big change
in plan and horizon.”
Neural interfaces may be opening windows into the brain, but often scientists
aren’t sure what they’re seeing through those newly opened windows. Neuronal
plasticity—the sprouting and weaving of neuron circuits—allows the cortex of a
prosthesis user to gradually repattern itself to make sense of nonsense. But increased
use of smart prostheses, and the experience that comes with this implementation, is
bringing another level of neuroplasticity into view. Smart prostheses don’t just
promote neuronal sprouting, they can persuade whole sections of the cerebral cortex,
the gray matter that comprises the outermost layers of the brain, to reorganize.
When a part of the cortex stops receiving signals from the body (as in deafness,
blindness, or spinal cord injury) or is physically damaged (as in stroke), the cortex
can restructure to cope, to reassign the healthy but out-of-service circuitry to new
functions. If you cut off the pointer finger so that the part of the motor cortex
corresponding to that finger stops receiving signals, the unused “pointer finger” turf
will be taken over by the remaining fingers, as demonstrated by the monkey
research.
More surprising still, sections of the cortex designed to perform one function
can learn another if prompted. Studies have shown that when blind children develop
Braille skills, essentially reading with their fingertips, the section of cortex dedicated
to tactile sensation actually takes over the part that would be vision. This is
14
impossible in even the most advanced computer. “If there’s one area that’s dedicated
to RAM,” explained Humayun, “it can’t all of a sudden start doing ROM. Your
brain can.”
Neuronal plasticity may help the brain to make sense of nonsense, but
neuroprosthetic innovators worried that cortical plasticity could create challenges.
Prior to implanting the retinal devices, Humayun and his team feared that due to
cortical plasticity the long-dormant vision region of the brain might have been
usurped by another function, particularly in the patient who had been blind for fifty
years. Perhaps the hearing region or tactile regions of the cortex had made use of the
latent biological machinery, as happens in people who are blind since birth.
But the implant worked, implying that a fair amount of the visual cortex was
preserved. Humayun said early testing is underway to measure just what happens in
the brain as the person learns to use the implant, particularly which region or regions
of the plastic brain become responsible for the restored vision. “So far all outcomes
have exceeded our expectations,” he said. The task is in figuring out why.
“Necessity is the mother of invention,” wrote Greek philosopher Plato. So
when one considers that stroke is the leading cause of disability in the United States,
it is no wonder that the stroke rehabilitation therapy is a bustling research arena. A
stroke literally leaves a dead spot in the brain; an entire circuit board ceases sending
messages to part of the body. Sometimes a stroke occurs when a blood vessel
ruptures, but most often a blood clot blocks a channel in the brain and halts blood
flow downstream. No blood means no oxygen means cell death. While symptoms of
15
a stroke depend on what part of the brain the blockage affected and for how long,
stroke victims often lose motor function (the ability to walk or use one or both arms),
speech, and suffer from chronic, debilitating pain as a result of atrophied and spastic
muscles.
Just as in sensory disorders, medical dogma of the past held that, after stroke,
“what’s done is done.” Some physicians still tell their patients that after six months
of stroke therapy they can no longer improve, according to Carolee Winstein,
Professor of Biokinesiology and Physical Therapy at the University of Southern
California. But patients are proving that’s just not true. Winstein notes that while
there may be no chance of repair for the specific dead spot in the brain, the function
that it once served can often return, thanks to rerouting in the brain, or detours
around the damage.
Paralysis does not imply faulty muscles, rather muscles that could work just
fine if they’d only be told what to do, when to contract. If the body reminds the
brain of the task—of what it should be controlling—the brain can often grow new
wires around the broken circuit board. (Some people, no matter how hard they are
pushed, can never regain function. The same flaccid paralysis of two different
patients can be caused by wildly different degrees of damage in the brain.)
Recent breakthroughs in physical therapy demonstrate that when a region of
the brain is damaged beyond repair, other healthy sections can pick up the slack to
restore lost function. For example, innovative techniques such as constraint-induced
(CI) therapy coach the brain and nervous system to rewire in a way that makes up for
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what was functionally lost. In constraint-induced therapy, a stroke patient’s stronger,
functional arm and hand are kept constrained for several weeks while the bad arm is
intensively trained to drive functional neurological recovery, in order to encourage
the development of detour circuits. “The goal is to develop rehabilitation strategies
that take advantage of the brain’s inherent capability to heal itself—strategies that
fire it up and get it to move in the right direction to optimize recovery,” said
Winstein. “We think about it as driving neuroplasticity.”
Neuroscientists and physical therapists alike have discovered that smart
prosthetic devices can assist immensely in this arena. Functional electrical
stimulation, or FES, produces functional movement in paralyzed or weakened
muscles by electrically stimulating the nerves within them using implanted
electrodes. “The results are miraculous,” said Warren Grill, professor of biomedical
engineering, surgery and neurobiology at Duke University. “But the mechanisms are
not. It’s all based on a trick.” Smart prostheses trick the body into thinking it is
communicating using natural electrical signals.
Picture a fly landing on your bare, big toe. The microscopic feet of that fine-
winged fellow brush the skin with just enough friction to create an itch. To shoo the
fly away, you contract your calf muscle to flick your foot. Your brain says, “muscle:
contract.” At this point, a cascade of electrical discharges is initiated in the brain and
sent careening down a series of neurons to the muscle. When this surge hits the end
of the nerve fiber in the muscle, the fiber emits stored chemical neurotransmitters
17
that bind to receptors on the muscle and deliver the message. The muscle heeds the
command: contract.
The only difference in functional electrical stimulation (FES) is the source of
that inaugural signal. And the muscle neither knows nor cares from whence that
signal came. One example of a cutting-edge FES device is the BION, developed by
Gerald Loeb’s Medical Device Development Facility at USC. The BION is an
injectable, wireless neurostimulator, hardly bigger than a grain of rice, which is
implanted in weak or paralyzed muscles to help them contract. The BION’s main
functions are to help disabled people strengthen their muscles and perform useful
movements (such as shifting the buttocks to prevent bed sores) while retraining their
brains and nervous systems.
Functional electrical stimulation devices like the BION work by translating
an electrical “control” signal into a “command signal” that tells a paralyzed muscle
to contract. In most FES systems, the control signal is recorded from a still-working
muscle. Take, for example, a man with a paralyzed hand. The patient cannot open
and close his hand (the useful function), but perhaps he can still deliberately, though
almost imperceptibly, flex his wrist. An implanted FES device can detect that tiny
twitch of his wrist and amplify it into a much larger signal. That signal is then
transmitted to electrodes implanted in the muscles that control the fingers,
stimulating them to contract in a coordinated way. The man learns to twitch his
wrist one way to open his hand, another to close it- and soon he can turn the
doorknob himself. He is in charge of the motion.
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“The patient has to feel like ‘it’s me moving my arm again,’” said Carolee
Winstein, who researches BION stroke therapy with Loeb. “We think that simply
drawing attention to the limb by trying to use the BION, or even having someone
watch it open and close their hand, enhances recovery. I can’t move their arm for
them for two hours while they read a magazine.” Just as reading a book involves
more than unmindfully passing your eyes over the words, relearning functional
control involves more that unmindfully “going through the motions.” Researchers,
physicians, and therapists agree that a huge amount of the neuroplasticity they’re
trying to evoke comes from the link between the intent to move and the actual
motion. And it takes a lot of practice. “If there is any chance they’re going to get
something back,” said Loeb, “practice is how they’re going to do it.”
Diligent practice comes more naturally for some than for others. Before Jen
French became a quadriplegic in a snowboarding accident a decade ago, she was the
type to wake up at 5 a.m. and jog five miles. “Life stopped with the injury,” she said.
But for the fiery, petite reddish-brunette, it didn’t stop for long. In 1999, a year and a
half after her 26-year-old body had launched off a ledge while she snowboarded with
her boyfriend Tim, French underwent more than seven hours of surgery to have a
then-experimental system implanted in her body that would allow her to stand again.
This “standing system,” developed under Hunter Peckham at the Cleveland
FES Center, is one of several functional electrical stimulation systems designed to
restore independence to people with spinal cord injuries. When French pushes a
button on a controller box the size of an old answering machine, eight electrodes
19
buried within the muscles of her thighs, hips, bum, and back incrementally dispatch
just enough electrical stimulation down implanted wires to help her rise from her
wheelchair.
French’s muscular legs are a far cry from the withered limbs of so many
people confined to life in a wheelchair. By standing and swinging her legs through a
walker, French even made her way down the aisle to Tim at their 2001 wedding.
Today, she often stands at the helm during Paralympic sailing. “The more you push
the technology,” said French, who constantly exercises her muscles using the
standing system, “the more you discover what it and your body can do.”
When the spinal cord is injured, some plasticity occurs automatically and the
spinal cord remodels to create spastic (usually useless, often problematic)
movements. But with training, these spastic movements could be made functionally
helpful. Peckham said early observations indicate that some paralyzed patients can
gain back vestiges of voluntary function by training with FES. A once fully
immobile leg or hand inexplicably becomes able to move, ever so slightly, on its
own. Since the motor signals aren’t coming from the brain, this voluntary movement
suggests that the spinal cord is processing the signals and modifying itself based on
repeated muscle activity. It’s as if a muscle, contracting with the help of FES,
whispers earnestly, “Look! Over here! Watch me move! Remember?” The spinal
cord, apparently capable of forging new neural pathways to send and receive motor
signals, seems to be listening.
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Neuroplasticity may be helping with sensory restoration in the paralyzed
body as well. Jen French has an incomplete spinal cord injury, meaning that some
signals can still make it back to her brain. She still has sensation in much of her legs,
and believes the FES standing system has helped maintain that. Similarly, Carolee
Winstein and her colleagues, in their work on stroke rehabilitation, have noticed that
when people start using their limbs again, they invariably report that they feel them
better. (Stroke usually effects both sensation and motor control.) “We think that’s
partly true because of plasticity,” she said, “because the motor and sensory cortices
are intricately connected through horizontal pathways. We might be getting the
plasticity in the motor cortex, but it’s having an effect on its neighbor.”
With all smart prosthetic devices in the early stages, researchers willingly
admit that they still don’t know more than they do. But fountains of knowledge about
the brain and nervous system are bubbling up everywhere with the evolution of smart
prosthetics. “We’re just beginning to get a sense of what’s going on, of what’s
changing in the brain,” said John Donoghue, a neuroscientist at Brown University.
Whereas many developers of neuroprosthetic devices have been working to
send electrical messages into the brain or nervous system, such as with sensory
implants and FES, Donoghue and his colleagues, among others around the world, are
working to wheedle information out. Donoghue’s experimental system, called
BrainGate, records brain activity in the motor cortex and uses that electrical
information to control an external device, such as a computer cursor, a wheelchair, or
a robotic hand. “We’re reconnecting the brain to the outside world,” Donoghue said.
21
The brain needs reconnecting to the world because otherwise the patient has
no way to move, no way to communicate, no way out. The motor commands are
locked in the brain (or at least trapped above the spinal cord injury) so the person
becomes “locked in” as well, unable to move, sometimes even unable to speak. In
conditions such as brain-stem stroke, Lou Gehrig’s disease (amyotrophic lateral
sclerosis), and spinal cord injury, the brain can properly create motor commands, but
has no way to turn those commands into action.
By translating intention into action, BrainGate lets people out of the shells
that confine them. The information that directs the BrainGate system is recorded by
4 x 4 millimeter array of 100 hair-thin microelectrodes poked gently into the soft
tissue of a person’s motor cortex. Like a stereo’s equalizer registering the rat-a-tat of
a snare drum, the electrodes record the firing, or spiking, of the patient’s neurons. A
processor then decodes that information into meaningful cues. When the person
thinks about moving his hand one direction, the cursor follows. To “click the
mouse,” he thinks about squeezing his hand.
“What was most surprising to me was that in every case, the part of the brain
we were looking at—the part that has not been involved in controlling movement in
years—is still putting out signals to control the arm,” said Donoghue. Even his own
past research had shown that dormant regions of the cortex are often taken over by
neighboring regions, like the tactile region of the brain in Braille-reading children
taking over the vision region. But, like Mark Humayun with the retinal implant, he
22
was thrilled to find out that as many as nine years post-injury, the motor regions of
the brain could still manifest motor signals.
Early pilot trials of BrainGate have been conducted in four people, with two
more clinical trials (of five people each) in the works. Donoghue said that although
they’re only beginning to get a sense of how the brain reorganizes to control the
devices, the patients exhibit learning and improvement over time. Interestingly, the
patient eventually stops thinking about moving his own arm to control the cursor,
and just thinks about moving the cursor. The motor cortex integrates the system as
thought it were a limb. It assimilates a new tool.
John Donoghue and Hunter Peckham have joined forces to marry BrainGate
sensor technology with functional electrical stimulation; to use the brain’s own
motor signals to drive stimulation electrodes in a person’s muscles. The five-year
goal is to enable a tetraplegic person to feed himself. “I will be so bold as to say that
way, way down the road, I think that paralyzed people will be able to walk without
having their disability detected,” said Donoghue. “But who knows, before then they
could figure out how to regenerate the spinal cord with stem cells and it won’t
matter.”
While patients’ nervous systems may become comfortable with the neural
interfaces, the patients have much more complicated feelings. Michael Chorost
certainly wasn’t sure about his cochlear implant at first. “It was obscurely
frightening,” he said. “How was this thing with all these wires and programming
actually going to work with all the warm squishy stuff in there?”
23
Chorost eventually made peace with mechanical nature of his implant, but
sometimes still struggles with whether he “owns” it in the same sense that he owns
his arm or leg. Similarly, Jen French said at first she couldn’t stop thinking about
her implanted system. “But it changes over time,” said French. “You just expect it to
work once it becomes part of you.”
Rather than feeling more machine-like as they integrate their bodies with
technology, neural prosthesis users often describe feeling more human and more
confident of their place in the human world. The value of being able to hear a voice,
to see a friend, to rise from a chair, or to speak a word, cannot be underestimated.
“No patient has ever said, ‘I want to play piano,’ explained Hunter Peckham. “It’s ‘I
want to be able to stand at the podium. I want to have a drink at the bar with my
friend. I don’t want to be fed at a restaurant.”
A few years ago, Jen French’s husband was out of town when Hurricane
Charlie descended upon their community in coastal Florida. Using her FES system,
French got busy battening the hatches, storing everything away in high cupboards
and shelves. “I never anticipated how much more functional I could be,” she said.
“I think that in our society to be human is to be free,” said Warren Grill.
“These devices aren’t taking over decisions. They’re all enablers of freedom.”
One day as we spoke over the phone, I asked John Donoghue, innovator of
the BrainGate system, to bear with me as I feverishly scribbled notes to capture our
conversation. With a chuckle, he remarked, “wouldn’t it be great to have a neural
interface system and the words could just show up on a screen?”
24
“Definitely,” I replied laughing.
Would that make me more free? Probably not. But someone who had spent
the last decade speaking only with his eyes? Absolutely.

25
BIBLIOGRAPHY

Begley, Sharon. Train Your Mind, Change Your Brain. New York: Ballantine
Books, 2007.

Chase, Victor D. Shattered Nerves: How Science is Solving Modern Medicine’s
Most Perplexing Problem. Baltimore: John Hopkins University Press, 2006.

Chorost, Michael. Rebuilt: My Journey Back to the Hearing World. New York:
Houghton Mifflin, 2005.
-- Personal Interview. 15 February 2007.

Donoghue, John. Personal Interviews. 15 February 2007, 2 March 2007.

French, Jennifer. Personal Interview. 26 February 2007.

Grill, Warren. Personal Interview. 15 February 2007.

Humayun, Mark. Personal Interview. 27 February 2007.

Loeb, Gerald. Personal Interview. 23 February 2007.

Merzenich, Michael. “Smart Prosthetics” Session at the Annual Meeting of the
American Association for the Advancement of Science. 15 February 2007.

Peckham, Hunter. Personal Interviews. 15 February 2007, 22 February 2007.

Winstein, Carolee. Personal Interview. 26 February 2007.

Abstract (if available)

Abstract In recent years, neuroscientists and biomedical engineers together have made great strides in patching once-impassible gaps in the nervous system's electrical matrix with neural prostheses. Cutting-edge neural or "smart" prostheses are nothing like the past generation of prostheses, which sit mute and lifeless next to the body's natural systems. Smart prostheses actually speak the electrical language of the body, and can help train or retrain the nervous system by taking advantage of the neuroplasticity of the brain and nervous system. The human body can integrate neuroprosthetic technology to enable remarkable recovery from deafness, blindness, and paralysis, among other conditions. This article discusses the cochlear implant, retinal implant, functional electrical stimulation devices and the cortical implant known as BrainGate. Rather than feeling more machine-like as they integrate their bodies with technology, neural prosthesis users often describe feeling more human and more confident of their place in the human world.

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University of Southern California Dissertations and Theses

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Development of implantable Parylene-based MEMS technologies for cortical applications

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Creator Poland, Haley S. (author)

Core Title Smart prosthetics: teaching the body with technology

School Annenberg School for Communication

Degree Master of Arts

Degree Program Journalism (Print Journalism)

Degree Conferral Date 2007-05

Publication Date 04/19/2007

Defense Date 04/02/2007

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag biomedical,implant,OAI-PMH Harvest,plasticity,prosthesis,Technology

Language English

Advisor Kotler, Jonathan (committee chair), Cole, K.C. (committee member), Gutierrez, Felix Frank (committee member)

Creator Email hpoland@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m419

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Identifier etd-Poland-20070419 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-475577 (legacy record id),usctheses-m419 (legacy record id)

Legacy Identifier etd-Poland-20070419.pdf

Dmrecord 475577

Document Type Thesis

Rights Poland, Haley S.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu