Temporary inactivation of the perirhinal cortex by muscimol injections block acquisition and expression of fear-potentiated startle.

The present study examined the role of the perirhinal cortex (PRh) in aversive information processing and emotional learning. Specifically, we studied the effects of temporary inactivation of the PRh on acquisition and expression of conditioned fear as measured by fear-potentiated startle in rats, as well as on shock sensitization of startle. Temporary inactivation of the PRh was induced by local injections of the GABAA agonist muscimol (0.0, 1.1, 2.2, 4.4 nmol/0.5 micro L). Muscimol injections into the PRh blocked both the expression and acquisition of fear-potentiated startle, as well as shock sensitization of startle. Shock sensitivity was not affected by muscimol injections, indicating that the observed blockade of acquisition and shock sensitization was not caused by a disruption in the perception of shock. Taken together, the present data show that the PRh is critical for the processing of aversive information and is necessary for the expression of emotional learning.