Neural substrate of spatial memory in the superior colliculus after damage to the primary visual cortex

In the primate brain, the primary visual cortex (V1) is a major source of visual information processing in the cerebral cortex, although some patients and monkeys with damage to the V1 show visually guided behaviors in the visual field affected by the damage. Until now, behaviors of the surviving brain regions after damage to V1 and their contribution to the residual visual functions remain unclear. Here, we report that the monkeys with a unilateral lesion of V1 can make not only visually guided saccades but also memory-guided saccades (MGS) into the affected visual field. Furthermore, while the monkeys were performing the MGS task, sustained activity was observed in a large fraction of the neurons in the superior colliculus ipsilateral to the lesion, which has been supposed as a key node for recovery after damage to V1. These neurons maintained the spatial information throughout the delay period regardless of whether they exhibited saccadic bursts or not, which was not the case on the intact side. Error analysis revealed that the sustained activity was correlated with monkeys' behavioral outcome. These results suggest that the ipsilesional SC might function as a neural substrate for spatial memory in the affected visual field. Our findings provide new insight into the understanding of the compensatory mechanisms after damage to V1.