one running direction also had unidirectional behavioral correlates, and all cells that were theta phase-locked in both running directions also responded in both directions to particular behaviors. A subsequent study investigated the influence of hippocampal theta phase-locking of mPFC neurons on working memory, one of the main functions associated with mPFC [16]. Rats were tested on a continuous spatial alternation task that included choice epochs requiring working memory and forced turn epochs with no working memory requirements. mPFC cells were more strongly phase-locked to hippocampal theta during correct choice epochs than during forced turns and errors. Correct choices were also associated with enhanced theta coherence between mPFC and hippocampus. Similar findings were obtained in another study of memory in which rats performed a delayed non-match to sample task [24]. Nearly half of mPFC cells were phase-locked to hippocampal theta on correct trials, while less than 20% of cells were phase-locked on error trials. Taken together, the results of these studies support the conclusion that mPFC–hippocampal theta phase-locking is relevant for functions that are carried out by the hippocampus and mPFC, such as goal directed behavior during navigation tasks and spatial working memory.
