Soc. Neurosci. Abstr. 1996.11

ROLE OF GABAERGIC INHIBITION IN GENERATION OF VISUAL RESPONSE PROPERTIES OF INFERIOR TEMPORAL CORTEX NEURONS IN THE MONKEY.

Y. Wang*, I. Fujita and Y. Murayama, Dept. Cognitive Neurosci., Osaka Univ. Med. Sch., Suita, Osaka 565, Japan.

Neurons in area TE of the monkey inferior temporal cortex respond to particular visual features of objects. Stimuli required for strong activation of most TE neurons are more complex than simple spots, bars or gratings. The examples include a T shape, a striped square, or a colored star. Little is known about where and how this stimulus selectivity is generated, although it has been suggested to be created in earlier cortical areas (V4 and TEO). In this study we applied bicuculine methiodide (BMI: a GABA-A receptor antagonist) by microiontophoresis with tungsten-in-glass/micropipette assemblies onto TE neurons to investigate how GABAergic inhibition in the TE contributes to the stimulus-selective response properties. A monkey (Macaca fuscata) anesthetized with a mixture of N2O and O2 was used.
Effects of BMI application on individual TE neurons were stimulus-specific. BMI administration augmented visual responses to some effective stimuli, but did not affect those to others. Moreover, in the presence of BMI, some cells began to respond to stimuli which did not evoke responses in them without BMI application. The latter effect was observed for a particular range of stimuli which often activated other neurons along the same or surrounding recording tracks. A general increase of neuronal excitability such as a lowered threshold does not explain these effects. Application of pH-matched vehicle did not affect the responses. We suggest that a generation process of the stimulus selectivity still goes on in the TE and that GABAergic inhibition contributes to this process.
Supported by grants from the Casio Science Foundation, and the Ministry of Science, Culture, and Education, Japan, to I.F.

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