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CORTICAL SYNAPTIC CIRCUITRY UNDERLYING VISUAL
PROCESSING IN THE PRIMARY VISUAL CORTEX
by
Baohua Liu
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PHYSIOLOGY AND BIOPHYSICS)
May 2010
Copyright 2010 Baohua Liu
Object Description
| Title | Cortical synaptic circuitry underlying visual processing in the primary visual cortex |
| Author | Liu, Baohua |
| Author email | baohuali@usc.edu; liubh_wisc@hotmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Physiology & Biophysics |
| School | Keck School of Medicine |
| Date defended/completed | 2010-02-09 |
| Date submitted | 2010 |
| Restricted until | Unrestricted |
| Date published | 2010-05-03 |
| Advisor (committee chair) | Zhang, Li I. |
| Advisor (committee member) |
Sampath, Alapakkam P. Chen, Jeannie Chow, Robert HP. Farley, Robert A. |
| Abstract | The simple-cell receptive field (RF) structure is an attractive and unique feature of the primary visual cortex, which is thought to reflect the circuitry principles governing orientation selectivity. Synaptic inputs underlying spike RFs are key to understanding mechanisms for neuronal processing. The well-known push-pull model, which is proposed to explain the synaptic mechanism under simple-cell RFs, predicts that in simple cells the spatially separated excitation and inhibition does not interact with each other and that simple inhibitory neurons exist in the primary visual cortex (V1). However, previous experimental results suggest that synaptic inhibition plays an important role in shaping RF properties in the visual cortex. The synaptic mechanisms underlying simple-cell RFs remain not well understood, partly due to difficulties in systematically studying functional properties of cortical inhibitory neurons and precisely measuring excitatory and inhibitory synaptic inputs in vivo.; In the first part of this project, to explore the functional properties of inhibitory neurons, we established two-photon imaging targeted cell-attached recordings from genetically labeled inhibitory neurons and nearby “shadowed” excitatory neurons in the primary visual cortex of adult mice. We found that in layer 2/3 the majority of excitatory neurons exhibited both On and Off spike subfields, with their spatial arrangement varying from being completely segregated to overlapped. On the other hand, most layer 4 excitatory neurons exhibited only one discernable subfield. Interestingly, no RF structure with significantly segregated On and Off subfields was observed for layer 2/3 inhibitory neurons of either the fast-spike or regular-spike type. They predominantly possessed overlapped On and Off subfields with a significantly larger size than the excitatory neurons, and exhibited much weaker orientation tuning. These results suggest that different from the push-pull model of simple cells, layer 2/3 simple-type neurons with segregated spike On and Off subfields likely receive spatially overlapped inhibitory On and Off inputs, which can enhance the spatial distinctiveness of On and Off subfields through a gain control mechanism.; In the second part, to explore the synaptic mechanism underlying simple cells, we applied whole-cell voltage-clamp recordings to mouse V1 neurons to reveal the spatial patterns of their excitatory and inhibitory synaptic inputs evoked by On and Off stimuli. Surprisingly, neurons with either segregated or overlapped On/Off spike subfields exhibited substantial overlaps between all the four synaptic subfields. The segregated RF structures are generated by the integration of excitation and inhibition with a stereotypic pattern: the peaks of excitatory On/Off subfields are separated and flank co-localized peaks of inhibitory On/Off subfields. The small mismatch of excitation/inhibition leads to an asymmetric inhibitory shaping of On/Off spatial tunings, resulting in a great enhancement of their distinctiveness. Thus, slightly separated On/Off excitation together with intervening inhibition can create simple-cell-like RF structure, and the dichotomy of RF structures may arise from a fine-tuning of the spatial arrangement of synaptic inputs.; Taken together, our findings imply that in mouse V1the push-pull circuit may not be the dominant mechanism to generate simple cells, and that alternatively simple-cell RFs can emerge from the interaction of overlap-but-mismatch excitatory and inhibitory synaptic inputs. |
| Keyword | mouse; interneuron; excitation; inhibition; vision |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2980 |
| Contributing entity | University of Southern California |
| Rights | Liu, Baohua |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Liu-3515 |
| Archival file | uscthesesreloadpub_Volume40/etd-Liu-3515.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | CORTICAL SYNAPTIC CIRCUITRY UNDERLYING VISUAL PROCESSING IN THE PRIMARY VISUAL CORTEX by Baohua Liu A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (PHYSIOLOGY AND BIOPHYSICS) May 2010 Copyright 2010 Baohua Liu |
