Download Effects of microstimulation in cortical area V4 on fine disparity

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