Gabriel Hunt¹, Dipin Kapila¹, Edward Ester¹; ¹University of Nevada, Reno

Contemporary neuroimaging research supports a sensory recruitment model of working memory (WM), where top-down signals originating in frontal and parietal cortex coordinate the storage of mnemonic information in sensory cortical areas. Communication between frontoparietal and sensory areas during WM is established and maintained via neural oscillations. Mounting evidence suggests that neural oscillations frequently take the form of traveling waves, or spatially coherent oscillations that propagate across the cortex. Whether and to what extent traveling waves contribute to the encoding, maintenance, and updating of WM content is unknown. Here, we explored this issue by tracking hemisphere-specific traveling waves while participants encoded, updated, and held information in WM. We recorded EEG while participants remembered the orientations of two colored bars – one per visual hemifield – over a short delay. At the end of each trial, a retrospective color probe instructed participants to recall the orientation of one bar as precisely as possible. During each trial, a third bar (“update stimulus”) was presented in the left or right visual hemifield midway through the delay period. On 50% of trials, a cue instructed participants to remember this new bar rather than the one it replaced (“replace” trials); on the remaining 50% of trials a cue instructed participants to ignore the new bar and continue remembering the original bar presented in the same location (“hold trials”). Analyses of cortical traveling waves time-locked to the onset of the update stimulus revealed a low-frequency (4-6 Hz), feedback (i.e., frontal-to-occipital) traveling wave over electrode sites contralateral to the location of the update stimulus during replace but not hold trials. This wave was distinct from a second low-frequency, feedforward (i.e., occipital-to-frontal) traveling wave evoked by a subsequent recall probe. These results provide preliminary evidence linking hemisphere-specific traveling waves of cortical activity to the encoding of new WM content.