Reconstructing stimulus-specific working memory representations in human visual, parietal, and frontal cortex.

摘要

Visual working memory (WM) enables the temporary storage of information in an "online" state. Substantial evidence suggests that WM storage is mediated by a broad network of frontal, parietal, and sensory cortical regions, but the precise contribution(s) of these regions to storage are unclear. One emerging view a?? informed by invasive electrophysiological recordings in non-human primates and human neuroimaging work - is that stimulus-specific information is represented by sustained patterns of activation in visual cortex, while sustained delay-period-specific responses in frontoparietal regions reflect the operation of "top down" attentional factors that refresh these sensory representations and/or mitigate the influence of distracting information. However, here we show that sustained patterns of activation observed in parietal cortex during WM storage faithfully represent specific features of a remembered stimulus. On each trial, participants were shown two gratings (one per visual hemifield) and postcued to remember one of these stimuli over a 10 second delay. Participants then adjusted the orientation of a "probe" grating to match the remembered target. Using fMRI and a forward encoding model of orientation selectivity, we attempted to reconstruct orientation-selective response profiles in functionally defined regions of visual (V1-hV4v/V3a), and parietal cortex (IPS0-3), as well as an anatomically defined region of frontal cortex implicated in WM storage (sPCS). This analysis revealed robust, graded orientation-selective response in multiple visual (V1-hV4) and inferior parietal (IPS0-1) ROIs both contralateral and ipsilateral to the cued grating (but not the uncued grating). Conversely, orientation-selective responses could not be recovered in any of the superior parietal (IPS2-3) or frontal (sPCS) ROIs that we examined. These results suggest that both visual and inferioparietal cortex play an important role in representing specific stimulus attributes during WM storage.