Effects of lateral and medial septal lesions on response suppression maintained by response-contingent and response-independent shock

Rats with electrolytic lesions in the medial (MS) or lateral (LS) septal areas were allocated to groups on electrophysiological criteria (loss or persistence of hippocampal theta rhythm, respectively) subject to subsequent histological checking. They were trained to press a lever for sucrose reward on a random interval (RI) schedule and while leverpressing were presented with two stimuli, each associated with a different schedule of shock delivery: in the presence of one, shocks occurred on an RI schedule irrespective of the rat”s behavior; in the presence of the other, shocks were programmed by the same schedule but delivered only when the rat pressed the lever. Both stimuli suppressed leverpressing. MS, but not LS, lesions significantly increased baseline RI responding; LS, but not MS, lesions significantly disinhibited responding suppressed by signaled shock, whether or not the shock was response-contingent. These changes were related to the effects of MS and LS lesions on hippocampal theta.