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Paper   IPM / Cognitive Sciences / 13965
School of Cognitive Sciences
  Title:   Maintenance of spatial information modulates the correlated variability of MT neurons based on their spatial selectivity
1.  Y. Merrikhi
2.  M. Parsa
3.  B. Noudoost
  Status:   In Proceedings
  Proceeding: SFN 2015
  Year:  2015
  Supported by:  IPM
Previous studies have shown that maintaining spatial information improves the discrimination of visual targets at the remembered location.Changes in the correlations in trial-to-trial variability of pairs of extrastriate neurons (noise correlations) have been proposed as a means for improving visual discrimination. We studied how memory-related spatial signals modulate the correlated activity of pairs of neurons within extrastriate areas, and the degree to which these modulations depend on the similarity between the spatial and feature selectivity of the two neurons. In two macaque monkeys, multiple neurons in the middle temporal area (MT) were simultaneously recorded using 16-channel linear array electrodes. The spatial selectivity of the neurons was quantified by measuring their response to probes presented in a 7x7grid centered around their estimated receptive field (RF). Feature selectivity was measured in a separate task in which moving gratings with 8 different directions of motion were presented within the neuron's RF. To test whether the maintenance of spatial information alters the correlated variability of these neurons, we then recorded their activity during the memory guided saccade task. The animal had to remember the location of a target and maintain fixation throughout a 1s delay period, then saccade to that location at the end of the trial. The noise correlations between pairs of MT neurons were measured both prior to target presentation and during the memory period of the task. Pairs of neurons were categorized based on whether the remembered location fell within one, both, or neither of the neurons’ RFs. Our results indicate that maintenance of spatial memory changes the correlations in activity between pairs of neurons, and that this change depends on the arrangement of the neurons' RFs relative to the remembered location. In contrast, the degree of feature similarity within a pair had negligible effect on the changes in their noise correlation during memory maintenance. These findings demonstrate how the top-down spatial signal interacts with the spatial and feature preferences of neurons within extrastriate areas, providing a more complete picture of how these changes in correlated activity can contribute to enhancing visual representations.

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