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Laminar processing of stimulus orientation in cat visual cortex
Author(s) -
Martinez Luis M.,
Alonso JoséManuel,
Reid R. Clay,
Hirsch Judith A.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.012776
Subject(s) - visual cortex , receptive field , stimulus (psychology) , depolarization , orientation (vector space) , selectivity , laminar flow , excitation , optics , neuroscience , chemistry , biophysics , physics , materials science , geometry , psychology , mathematics , biology , thermodynamics , biochemistry , quantum mechanics , psychotherapist , catalysis
One of the most salient features to emerge in visual cortex is sensitivity to stimulus orientation. Here we asked if orientation selectivity, once established, is altered by successive stages of cortical processing. We measured patterns of orientation selectivity at all depths of the cat's visual cortex by making whole‐cell recordings with dye‐filled electrodes. Our results show that the synaptic representation of orientation indeed changes with position in the microcircuit, as information passes from layer 4 to layer 2+3 to layer 5. At the earliest cortical stage, for simple cells in layer 4, orientation tuning curves for excitation (depolarization) and inhibition (hyperpolarization) had similar peaks (within 0–7 deg, n = 11 ) and bandwidths. Further, the sharpness of orientation selectivity covaried with receptive field geometry ( r = 0.74 ) ‐ the more elongated the strongest subregion, the shaper the tuning. Tuning curves for complex cells in layer 2+3 also had similar peaks (within 0–4 deg, n = 7 ) and bandwidths. By contrast, at a later station, layer 5, the preferred orientation for excitation and inhibition diverged such that the peaks of the tuning curves could be as far as 90 deg apart (average separation, 54 deg; n = 6 ). Our results support the growing consensus that orientation selectivity is generated at the earliest cortical level and structured similarly for excitation and inhibition. Moreover, our novel finding that the relative tuning of excitation and inhibition changes with laminar position helps resolve prior controversy about orientation selectivity at later phases of processing and gives a mechanistic view of how the cortical circuitry recodes orientation.