Septal Lesions Potentiate Freezing Behavior to Contextual but Not to Phasic Conditioned Stimuli in Rats

The effects on freezing behavior elicited by contextual and phasic conditioned stimuli (CSs) were examined in rats with septal lesions. Two weeks after surgery, blocks of 2 conditioning trials con sisting of a tone (10 kHz, 75 dB, 20 s) paired with a footshock (500 ms, 0.5 mA) were presented on 2 consecutive days. Tone-alone trials were presented each day thereafter until extinction criterion was met. Septal lesions were found to potentiate the freezing response elicited by contextual stimuli but had no effect on freezing elicited by the phasic CS. The septum thus appears to be involved in the acquisition and/or expression of defensive behaviors elicited by contextual stimuli.