An ensemble code in medial prefrontal cortex links prior events to outcomes during learning

Abstract

The prefrontal cortex is implicated in learning the rules of an environment through trial and error. But it is unclear how such learning is related to the prefrontal cor-texs role in short-term memory. Here we asked if the encoding of short-term memory in prefrontal cortex was used by rats learning decision rules in a Y-maze task. We found that a similar pattern of neural ensemble activity was selectively recalled after reinforcement for a correct decision. This reinforcement-selective recall only reliably occurred immediately before the abrupt behavioural transitions indicating successful learning of the current rule, and faded quickly thereafter. We could simultaneously decode multiple, retrospective task events from the ensemble activity, suggesting the recalled ensemble activity had multiplexed encoding of prior events. Our results suggest that successful trial-and-error learning is dependent on reinforcement tagging the relevant features of the environment to maintain in prefrontal cortex short-term memory.