Effect of bilateral septal lesions on discrimination avoidance conditioning in rats.

Studies were performed, using the two-way shuttle box method, on the acquisition of discrimination avoidance by rats with bilateral lesions of the septum (septal rats) in relation to changes in emotional behavior. Septal rats exhibited hyperreactivity immediately after the lesions were made: their startle, struggle and vocalization responses to stimuli were markedly increased. These hyperemotional responses, however, decreased and returned to the normal level 7 days after surgery. Initially, the septal rats showed elevated conditioned avoidance responses to both the CS+ and the CS-. In later stages, their responses to the CS+ showed progressive and gradual increase, accompanied by a decrease in responses to the CS-, until responses to both stimuli were only slightly elevated above the level of control rats. These results suggest that bilateral lesions of the septum do not affect discrimination ability itself. The impairment of discrimination avoidance during the initial stages may result from the transient impairment of the discrimination acquisition process.