Soc. Neurosci. Abstr. 1999.10

HOW SELECTIVE AND RELIABLE ARE VISUAL RESPONSES OF INFERIOR TEMPORAL CORTEX NEURONS? : COMPARISON BETWEEN ANAESTHETIZED AND AWAKE CONDITIONS.

M. Kato2,3*, T. Uka1, I. Fujita1,2. 1Grad. Sch. Eng. Sci., Osaka Univ., 2CREST, JST, Toyonaka, Osaka 560-8531, 3Brain Func. Res. Grp., KARC, CRL, Nishi-ku, Kobe, Hyogo 651-2401, JAPAN

Neurons in area TE of the monkey inferior temporal cortex have been shown to respond to complex shapes, color, or texture. The reported degree of response selectivity, however, markedly differs among previous studies. This difference may result from a difference in the experimental procedure such as the state of monkeys during recording (anaesthetized vs. awake conditions) or the number and type of visual stimuli used in experiments. In order to examine the effect of animal state on responses of TE neurons, we compared visual responses of neurons sampled in nearly identical regions of area TE in a monkey (Macaca fuscata) between awake and anaesthetized conditions. We used a fixed set of 80 predetermined stimuli including black and white geometrical shapes and photographs of objects.
We obtained 194 and 60 extracellular multiple-unit activities under awake and anesthetized conditions, respectively, and 99 % of the recorded units showed statistically significant responses to more than one of the stimuli. The number of stimuli evoking a statistically significant excitatory response was larger under awake condition (range, 0-76; median 11) than under anesthetized condition (range, 1-30; median 3). The tuning width of selectivity measured as the half-peak width of the stimulus-response curve was not different between the two conditions. The variability of the response magnitude across multiple presentations of identical stimuli was larger under anesthetized condition, while the variability of spontaneous firing during a prestimulus period did not differ between the two conditions. Thus, despite the similar response tuning between awake and anaesthetized animals, neurons under an anesthetized condition may respond to a smaller number of stimuli compared to those under an awake condition due to larger variability of responses across stimulus presentations, and hence, a lower probability of responses being statistically significant (Supported by CREST)

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