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Masih Rahmati, Golbarg Saber, Clayton Curtis; Reconstructing the population dynamics of spatial priority in early visual cortex during working memory. Journal of Vision 2015;15(12):295. doi: https://doi.org/10.1167/15.12.295.
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The read-out of prioritized maps of space in frontal cortex is believed to provide the spatial feedback signals needed to bias activity in early visual cortex. These feedback signals can be spatially directed via a saccade plan. Maintaining a saccade plan in working memory, therefore, may evoke a pattern of activity in topographically organized population of neurons with a peak centered in the neurons with receptive fields that match the saccade goal. Here, we test for such population dynamics using a forward encoding model of the distributed patterns of fMRI activity in human visual cortex. First, using fMRI we measured neural activity in human visual areas V1, V2, V3, V3A/B, hV4 and IPS-0/1 while subjects maintained a planned saccade directed to or away from the location of a brief visual cue. Second, we mapped the retinotopic locations of memory-guided saccade cues within each visual area. Third, we developed a forward encoding model to reconstruct the neural population dynamics in early visual areas. In the forward model, we used a linear combination of outputs from a number of information channels (i.e., basis functions) to estimate each voxel’s response to visual cues at a variety of retinal locations. We validated the model by successfully reconstructing both the locations of both remembered visual cues and prospective saccade goals based on fMRI responses during working memory delay periods. Our ability to build a forward model that reconstructs the locations of maintained representations allows us to make strong inferences about the population dynamics of topographic visual areas and how these dynamics are related to working memory storage. Moreover, these results show that the population activity in early topographic areas is sculpted by top-down feedback signals representing spatial priority.
Meeting abstract presented at VSS 2015
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