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Rebecca A. Berman, Laura M. Heiser, Richard C. Saunders, Carol L. Colby; Visuospatial updating in the split-brain. Journal of Vision 2004;4(8):887. doi: 10.1167/4.8.887.
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© ARVO (1962-2015); The Authors (2016-present)
With each eye movement, the brain receives a new image from the retina, yet we perceive the visual world as stable. This suggests that the brain constructs visual representations that take our eye movements into account. In several cortical areas and in superior colliculus, neurons update or “remap” locations when the eyes move. These neurons fire in the single step task, in which a saccade brings the receptive field onto a previously stimulated location. Updating activity is also observed in the double step task, in which the animal makes sequential saccades to two target locations. We hypothesized that the forebrain commissures provide the primary route for updating spatial locations across visual hemifields. We tested this hypothesis by measuring the behavioral and physiological correlates of remapping in two split-brain macaques. In behavioral experiments, we compared two conditions of the double step task. For within-hemifield sequences, the representation of the second target (T2) was updated within a single hemifield. For across-hemifield sequences, T2 was updated from one hemifield to the other. Double-step performance was impaired for across-hemifield but not within-hemifield sequences. Across-hemifield sequences could be learned, however, as the animals gained experience. We investigated the neural correlates of updating by recording from neurons in the lateral intraparietal area. We compared activity for within- and across-hemifield conditions in the single step and double step tasks. Remarkably, neurons exhibited remapping activity not only for within-hemifield conditions, but also for across-hemifield conditions. Across-hemifield activity was nonetheless smaller in magnitude and later in onset. These behavioral and neural data suggest that (1) the forebrain commissures are the primary route for updating across visual hemifields, but (2) subcortical paths are integral for across-hemifield updating in the split-brain.
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