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Abstract

Presented at the The Society for Neuroscience Annual Conference 2015

Comparing two visual motion stimuli that occur at different times require processing and storage of the initial stimulus, followed by its retrieval and comparison to the current stimulus. Such tasks demand coordination of processes involving bottom-up sensory information and top-down cognitive signals. Prefrontal cortex (PFC) is likely to play a key role in this coordination since it receives inputs from the motion processing area MT and the activity of its neurons reflects task engagement and participation in sensory maintenance. When motion comparisons involve stimuli presented at the fovea, neurons in the lateral PFC (LPFC) show direction selective (DS) responses indicative of their MT origins and display anticipatory and memory-related activity, the likely components of their cognitive influences. Little is known about LPFC activity during tasks involving motion presented outside the fovea. This question is of interest because of the connectivity between LPFC and the highly retinotopic area MT: while the information about the contralateral motion can be supplied directly by MT in the same hemisphere, the ipsilateral motion represented by MT in the opposite hemisphere, can only reach LPFC indirectly, most likely via callosal connections from the opposite LPFC. We examined how the LPFC neurons represent and utilize motion information that originates in the ipsilateral and contralateral hemifields while monkeys compared directions of two stimuli, S1 and S2, separated by a delay. During S1, responses to the contralateral motion were stronger and preceded ipsilateral responses by ~40ms, an indication of the apparent dominance of direct inputs from the ipsilateral MT. The asymmetry between contralateral and ipsilateral responses during S1 was not reflected in their DS activity, since it was equally robust for both stimulus locations. During the S2, responses to the ipsilateral but not the contralateral stimuli were enhanced, eliminating the dominance of the contralateral signals observed during S1. In addition, the activity of many neurons during and after S2 for stimuli in each of the two hemifields was modulated by the direction of S1, reflecting the difference between current and remembered stimuli and was predictive of the perceptual report. These results demonstrate that the process of memory-guided stimulus comparisons seamlessly incorporates sensory information from both hemispheres. Thus, while the sensory components of the LPFC activity reflect the difference between their direct and indirect origins, it appears that its cognitive components can compensate for the inequalities in their bottom-up sensory signals.