Spatial Updating in Monkey Superior Colliculus in the Absence of the Forebrain

23 In previous studies, we demonstrated that the forebrain commissures are the primary pathway for 24 remapping from one hemifield to the other. Nonetheless, remapping in cortical area LIP across 25 hemifield is still present in split brain monkeys. This finding indicates that a subcortical structure 26 must contribute to remapping. The primary goal of the current study was to characterize 27 remapping activity in the superior colliculus in intact and split brain monkeys. We recorded 28 neurons in both the superficial and intermediate layers of the SC. We found that across29 hemifield remapping was reduced in magnitude and delayed compared to within-hemifield 30 remapping in the intermediate layers of the SC in split brain monkeys. These results mirror our 31 previous findings in area LIP. In contrast, we found no difference in the magnitude or latency 32 for within compared to across-hemifield remapping in the superficial layers. At the behavioral 33 level, we compared the performance of the monkey on two conditions of a double-step task. 34 When the second target remained within a single hemifield, performance remained accurate. 35 When the second target had to be updated across hemifields, the split brain monkeys’ 36 performance was impaired. Remapping activity in the intermediate layers was correlated with 37 the accuracy of the performance and latency of the second saccade during the across-hemifield 38 trials. Remapping in the superficial layers was correlated with latency of the second saccade 39 during the within and across-hemifield trials. The differences between the layers suggest that 40 different circuits underlie remapping in the superficial and intermediate layers of the superior 41 colliculus. 42 43 44