Corticostriatal Mechanisms of Gating Working and Short-Term Memories

Abstract

Working memory is frequently operationalized as information maintenance in the absence of sensory stimulation. A complete mechanistic understanding, though, needs to account for maintenance in the presence of distractors. While theoretical models fuse the separate contributions of corticostriatal areas at the service of working memory gating (O’Reilly & Frank, 2006), a unified exploration of the phenomenon at the neurophysiological level is still missing. To study these mechanisms, we trained two macaque monkeys to flexibly, on a trial-by-trial basis, memorize a target visual stimulus within a sequence. Presentation of that stimulus was preceded and followed by an arbitrary number of distractor items. We recorded neural activity at the temporal, prefrontal cortex, and striatum. Analysis of the neural data allows us to identify dissociable contributions that map to sensory and memory processing. We find that IT cells elicit a transient response selective to the presented stimulus, while dlPFC encodes memory information at different timescales. Our results highlight a possible boundary between short-term and working memories. Short-term memories appear to be unstable and prone to interference while working memories enter through gating in a stable subspace. We provide evidence for a prefrontal-striatal gating mechanism that allows the target stimulus to latch onto working memory. This mechanism appears to be operationally abstract and stimulus independent. Finally, we discuss further analyses that will allow us to explore further the implementational details of this mechanism.