Involvement of visual cortex in a visual working memory task: Evidence from steady-state visual potential frequency tagging

摘要

Working memory, the short-term maintenance of behaviorally relevant information, has robustly been shown to engage prefrontal cortex and attentional control networks in hemodynamic and electrophysiological studies. Work in the animal model has provided converging evidence, but has also pointed towards involvement of sensory cortices. In line with these findings, several current models of working memory emphasize aspects of selecting and amplifying sensory representations of the task stimulus during retention. Progress in the empirical testing of these notions has however been prevented by methodological issues with quantifying sensory responses to concurrently presented or retained stimuli of a memory set. The present study addressed this problem with three experiments using a steady-state potential frequency tagging approach: EEG data were collected from 47 participants during a visual working memory task, with the orientation of two grating stimuli being the task-relevant dimension. After a retention interval, probe gratings were presented again, while phase reversing at two different fixed rates to elicit steady-state visually evoked potentials. Observers then made either a matcho-match decision or they manually set one probe grating at the remembered orientation. Results show an enhanced steady-state signal over visual cortical areas for stimuli being held in working memory, compared to non-matching stimuli. These data suggest that early visual neurons are actively involved in the process of working memory. Future work may use the visual electrocortical response as a reference signal for studying interactions among brain regions involved in working memory.