Working memory is a global process with an embedded hierarchy for mnemonic representations

Feature-based visual working memory representations are thought to be maintained across widely distributed areas of sensory and association cortices. However, the extent of the participating circuit and the nature of the representations are a matter of vigorous debate. We made microelectrode recordings from 42 cortical areas in monkeys performing a feature-based visual working memory task and an interleaved fixation task. We demonstrate that visual working memory produces widespread changes in cortical activity, while mnemonic representations are more restricted, hierarchically organized, and maintained by an active recruitment mechanism that prevents memories from rapid decay. We also find that microsaccadic eye movements during the memory delay encode the stimuli held in memory, suggesting that mnemonic representations maintain a semblance of the real image. Collectively, these findings support a framework in which most cortical areas, within a modality, contribute to mnemonic representations at time scales that increase in a hierarchical manner.
Nicholas M. Dotson, Steven J. Hoffman, Baldwin Goodell, Charles M. Gray