Expressing learned, but not innate, fear requires the prefrontal cortex.

Corcoran and Quirk have blocked nerve signals (using the sodium channel blocker tetradotoxin) in the prelimbic subregion of the medial prefrontal cortex (PL) of rats during fear learning and expression. Inactivation of PL reduced freezing to both a tone and a context that had been previously paired with footshock (learned fear) but had no effect on freezing to a cat (innate fear). Inactivation of PL before conditioning, however, did not prevent the formation of auditory or contextual fear memories. Thus, activity in PL is critical for the expression, but not the acquisition, of learned fears. They suggest that PL integrates information from auditory and contextual inputs and regulates expression of fear memories via projections to the basal nucleus of the amygdala.