Neural correlate of visual awareness in the superior colliculus of the animal model of blindsight

Abstract

Human blindsight patients, who have damages in the primary visual cortex (V1), can discriminate the target positions while they deny awareness of the targets. Macaque monkeys with a unilateral lesion in V1 have been used as an animal model of blindsight. Here we sought for neural activity related to blindsight behavior. First, we examined whether the monkeys showed behavior analogous to human blindsight patients. Two macaque monkeys with a unilateral V1 lesion were tested with two saccade tasks. 1) A forced-choice (FC) task, in which the saccadic target comes on one of two possible positions, requires discrimination of target positions. 2) A yes-no (YN) task, in which the monkeys have to maintain fixation when the saccadic target is absent, requires detection of the target. When the target was presented in the ipsilateral hemifield, the monkeys' performance was more than 95 % in both tasks. On the other hand, when the target was presented in the contralateral hemifield, the monkeys had a better performance in the FC task than the YN task. These results suggest that the monkeys exhibit behavior that parallels to the human blindsight patients. Next, we recorded neural activities from the superior colliculus (SC) of the monkeys performing the YN task. The tasks were modified as a delayed saccade version so that the neural response to the visual target was dissociable from saccade-related activity. We found that the transient response of the ipsilateral SC to the visual target was larger when the monkeys successfully detect the target than when the monkeys missed it in the YN task. Such modulation was not found in the contralateral SC. We conclude that the transient response in the ipsilateral SC comprises a part of neural correlates of reduced visual awareness specific to blindsight.