Abstract

This study investigated functions of medial septum and/or hippocampal θ rhythm, and multiple unit response in the hippocampus during extinction of classical conditioning of rabbit`s nictitating membrane response. In experiment 1, blocking of Hippocampal θ rhythm with medial septal lesion brought about resistance of extinction, but in initial extinction trials brought about performence deficiency. Namely, the size of response area in lesion group were less then in control group. So, former result could be explained in terms of arousal hypothesis, but latter result could not be explained. And, it was difficult to explain the result of experiment 1 with any other hypothesis. Hippocampal multiple unit response of medial septal lesion group did not differ from that of control group. This result suggest that there were no correlation between hippocampal θ rhythm and hippocampal unit response. In experiment 2, driving of hippocampal θ rhythm by electrical low frequency stimulation of medial septum brought about resistance of extinction. There was no statistical significance in the analysis of peak amplitude, response area, percentage of conditioned response. Namely, the strength of resistance was very great. In the analysis of multiple unit response, the result was similar to that of experiment 1. This results could be explained with the view which assert that medial septum serve to process frustrative stimuli, but could not be explained with arousal hypothesis. And, any hypothesis could not explain both results of experiment 1 and experiment 2. So, these results should be approched with new viewpoint. In our discussion, it was presented that the approch of neural network or computational neuroscience can suggest that function of medial septum and/or hippocampal θ rhythm were related to hippocampal-neocortex resonance loop to hippocampal index model.