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Effects of microstimulation in cortical area V4 on fine disparity discrimination 細かい視差弁別における大脳皮質 V4 野微小電気刺激の効果 塩崎 博史(Hiroshi M. Shiozaki):1 土井 隆弘(Takahiro Doi):1 田辺 誠司(Seiji Tanabe):1 藤田 一郎(Ichiro Fujita):1 1: 大 阪 大 院 ・ 生 命 機 能 ・ 認 知 脳 科 学 (Laboratory for Cognitive Neuroscience, Graduate School of Frontier Biosciences, Osaka University, Toyonaka, Japan) Responses of neurons in area V4, which encode the disparity of stereoscopic images, fluctuate to repeated presentations of the same disparity. Similarly, when a subject is discriminating a subthreshold disparity, its forced-choice decision fluctuates. V4 neurons are implicated in this decision-making because their responses correlate with the subject’s choice on a trial-by-trial basis. To explore a causal relationship between V4 responses and choice based on disparity, we examined whether electrical microstimulation of neural populations in V4 systematically affects the subject’s decision. We trained one monkey to indicate by eye movement whether a random-dot stereogram was perceived in front of or behind the surrounding annulus. The disparity was varied across trials such that it ranged above and below the psychophysical threshold. We applied current pulses during visual stimulus presentation in a randomly selected half of the trials. We quantified the effects of microstimulation by calculating the horizontal shift of the psychometric curves between with- and without-microstimulation trials. Microstimulation biased the monkey’s choice in more than one-third of the stimulated sites (7 of 21 near-preferring sites and 5 of 10 far-preferring sites; logistic regression, p < 0.05). Most of the significant biases were in the direction consistent with the disparity preference of the neural population at the stimulated site (5 of 7 near-preferring sites and 5 of 5 far-preferring sites). On average, microstimulation significantly shifted the psychometric curve (0.0021°, equivalent to 20% of the average psychophysical threshold) toward the direction of the disparity preference of the stimulated neurons (t test, p = 0.0043). From these results, we suggest that V4 neurons play a causal role in discriminating small differences in binocular disparity between center and surround of a visual stimulus. Supported by Kakenhi (17022025(IF)), CREST