Stimulus-Specific Delay Activity in Human Primary Visual Cortex

TLDR

Working memory is thought to be maintained by sustained activity in sensory areas that encode the information to be remembered. fMRI showed that although V1’s mean activity did not increase during the delay, multivoxel patterns remained sustained and reflected the stored feature, mirroring patterns seen during sensory discrimination.

Abstract

Working memory (WM) involves maintaining information in an on-line state. One emerging view is that information in WM is maintained via sensory recruitment, such that information is stored via sustained activity in the sensory areas that encode the to-be-remembered information. Using functional magnetic resonance imaging, we observed that key sensory regions such as primary visual cortex (V1) showed little evidence of sustained increases in mean activation during a WM delay period, though such amplitude increases have typically been used to determine whether a region is involved in on-line maintenance. However, a multivoxel pattern analysis of delay-period activity revealed a sustained pattern of activation in V1 that represented only the intentionally stored feature of a multifeature object. Moreover, the pattern of delay activity was qualitatively similar to that observed during the discrimination of sensory stimuli, suggesting that WM representations in V1 are reasonable “copies” of those evoked during pure sensory processing.