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| Paper IPM / Cognitive / 14965 |
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We have recently shown that in the absence of firing rate changes, a spatially-specific working memory (WM) signal drives subthreshold modulations in visual areas. Whether and how this subthreshold input results in enhanced visual
processing is crucial for understanding how sensory processing is altered by WM. We simultaneously recorded the spiking activity and local field potentials from multiple sites within the middle temporal (MT) cortex during a modified version of the memory guided saccade task. In this task, a set of visual probe stimuli are presented during the fixation and memory periods. We quantified the receptive fields (RFs) in MT and altered the locus of WM relative to each RF to study the effect of WM in isolation and when interacting with incoming visual
signals. In the absence of visual stimuli, there was a robust increase in the locking of spikes to the ongoing αβ oscillations when remembering a location near the MT RF, even though the overall firing rate remained unchanged.
Interestingly, in the presence of visual stimuli during the memory period, the WM-induced change in the locking between spikes and ongoing αβ oscillations was sufficient to enhance the ability of MT neurons to encode visual stimuli (quantified using the mutual information between the visual stimulus location and the phase of αβ oscillations at which spikes occurred). Importantly, the
increased gain and discriminability of the response to incoming visual stimuli occurs mostly during the preferred phase of ongoing αβ oscillations. This finding indicates that the WM-induced enhancement of the visual representation depended upon these oscillatory changes. These results provide a mechanistic understanding of how, by altering the oscillatory activity within visual areas, a spatially specific WM signal is capable of enhancing the
efficacy of visual sensory processing, potentially underlying the behavioral benefits of WM for visual perception.
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