Septal correlates of conditioned inhibition and excitation in rats

Multiple-unit activity was recorded in the lateral septum of rats during Pavlovian differential conditioning. In Experiment 1, one group of animals received a classical aversive discrimination paradigm, while another group was presented with a control procedure in which the unconditioned stimuli (shocks) were administered randomly with regard to the conditioned stimuli. Septal unit activity increased during presentations of the conditioned inhibitor and was markedly suppressed during presentations of the conditioned excitor in the conditioning-group animals and not in the control animals. Baseline activity remained unchanged in the conditioning group but was suppressed in the random control group. Furthermore, termination of the aversive stimuli was marked by a burst of firing in the conditioning group, but no such rebound was seen in the control group. In Experiment 2, a classical appetitive discrimination paradigm was given, in which septal unit activity was found to increase in the presence of the conditioned excitor and was suppressed in the presence of the conditioned inhibitor. The results are interpreted as indicating a role for the septum in the relief of aversive states.