Abstract

tion that pre- 1992). These authors found that stimuli at nonoptimal ventedthem from firing in response to the visual stimu- orientations suppressed the background activity of cor- lus. The visually evoked excitatory postsynaptic po- tical cells elevated by glutamate application or by the tentials (EPSPs) recorded during the period of cortical presentation of a conditioning stimulus at the preferred suppression, therefore, reflected largely the thalamic orientation. In addition, when GABA A -mediated inhibi- input. In 16 neurons that received monosynaptic input tion was blocked pharmacologically, the orientation se- from the thalamus, cortical suppression left 46% of lectivity of many cortical neurons was dramatically re- normal visual response on average (12%--86% in duced (Sillito, 1975; Daniels and Pettigrew, 1975; Tsumoto range). In those c

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