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Synaptic physiology of the flow of information in the cat's visual cortex in vivo
Each stage of the striate cortical circuit extracts novel information about the visual environment. We asked if this analytic process reflected laminar variations in synaptic physiology by making whole-cell recording with dye-filled electrodes from the cat's visual cortex and thalamus; the stim...
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Published in: | The Journal of physiology 2002-04, Vol.540 (1), p.335-350 |
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Main Authors: | , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Each stage of the striate cortical circuit extracts novel information about the visual environment. We asked if this analytic
process reflected laminar variations in synaptic physiology by making whole-cell recording with dye-filled electrodes from
the cat's visual cortex and thalamus; the stimuli were flashed spots. Thalamic afferents terminate in layer 4, which contains
two types of cell, simple and complex, distinguished by the spatial structure of the receptive field. Previously, we had found
that the postsynaptic and spike responses of simple cells reliably followed the time course of flash-evoked thalamic activity.
Here we report that complex cells in layer 4 (or cells intermediate between simple and complex) similarly reprised thalamic
activity (response/trial, 99 ± 1.9 %; response duration 159 ± 57 ms; latency 25 ± 4 ms; average ± standard deviation; n = 7). Thus, all cells in layer 4 share a common synaptic physiology that allows secure integration of thalamic input. By
contrast, at the second cortical stage (layer 2+3), where layer 4 directs its output, postsynaptic responses did not track
simple patterns of antecedent activity. Typical responses to the static stimulus were intermittent and brief (response/trial,
31 ± 40 %; response duration 72 ± 60 ms, latency 39 ± 7 ms; n = 11). Only richer stimuli like those including motion evoked reliable responses. All told, the second level of cortical
processing differs markedly from the first. At that later stage, ascending information seems strongly gated by connections
between cortical neurons. Inputs must be combined in newly specified patterns to influence intracortical stages of processing. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2001.012777 |