GABAERGIC INHIBITION CONTRIBUTES TO CONSTRUCTION OF RECEPTIVE FIELD STRUCTURES OF MONKEY INFERIOR TEMPORAL NEURONS

Yi Wang, Ichiro Fujita, Yusuke Murayama, Hiroshi Tamura.
Department of Cognitive Neuroscience, Osaka University Medical School
Graduate School of Engineering Science, Osaka University@
CREST, JST.

Receptive field (RF) properties of neurons in visual area TE of the inferior temporal cortex were investigated by blocking GABAergic inhibition in anesthetized monkeys. The normal RF size of TE neurons measured at half-peak response level along one dimension was 15.4±6.9°(mean±S.D.). In 95% of the neurons tested, blockade of inhibition enlarged their RFs by 9.1±6.1° at the original half-peak level, and enhanced visual responses of TE neurons to stimuli shown at the peripheiy of or outside their normal RFs where the stimuli originally evoked little or no response. The strongest disinhibition usually occurred in the center of RFs, but in some cells a strong disinhibition also occurred in peripheral regions. Excitatory inputs were strongest in the center of RFs, but some cells showed isolated "hot spots" (i.e., strongly responsive region) in the periphery, which were suppressed by inhibition under normal conditions but appeared with an administration of a GABA antagonist. We also noted that the retinal blind spot of the contralateral eye was represented within RFs of 4 neurons. One of them had another silent region similar to the retinal scotoma within its RF where effective stimuli could not elicit responses even under removal of GABAergic inhibition, suggesting that a region within RFs appeared to receive no visual inputs. We suggest that inputs from more extensive retinotopic regions than previously thought converge onto TE neurons, -and intrinsic GABAergic inhibition participates in sculpturing of normal RF profiles of TE neurons.


Back