Working memory and choice encoding in medial prefrontal cortex of rats performing a spatial double alternation task.
Neural correlates of working memory, errors, and response choice were identified in the medial prefrontal cortex (mPFC) of rats performing a spatial delayed double alternation task. The mPFC of rats has been associated with attention, working memory, emotional control, and other executive functions. Lesioning or inactivation of mPFC, the prelim- bic (PL) and infralimbic (IL) areas in particular, have been shown to produce significance decreases in performance of delayed response tasks. Previous recording experiments have found examples of neurons in mPFC that have elevated and selective activity during the delay period. However, these experiments have been quite simple compared to experiments in monkeys. For instance, many experiments in rats have used spatial alternation tasks but none have been able to successfully separate coding for past spatial goals from coding for future spatial goals. The aim of the experiment reported here was to develop a task with complexity similar to what is found in primate research and to record from mPFC as the rats performed the task. We developed a delayed double alternation, in which rats must respond in a left-left-right-right pattern. This task requires the rats to store and recall at least two items of information to receive rewards. After training rats to perform the task, we recorded from mPFC of awake behaving rats using chronically implanted tetrodes. We found groups of neurons encoding past goals, future goals, switch-stay strategy, and response errors. Encoding for past goals and future goals are performed by two separate, but over- lapping, ensembles of neurons. Anatomically, the mPFC is involved in neural circuits which serve to integrate internal and external stimuli into behavioral actions. Our results reveal a functional integration of the past, present, and future into action.