Hippocampal Electrical Activity in Spontaneous Behavior and Active Avoidance Conditioning in Rats

The purpose of this study is to examine previous theories of hippocampal electrical activity in relation to behavior with special emphasis on VANDERWOLF's hypothesis, based on new data with rats as subjects, in which hippocampal activity was studied during spontaneous behavior patterns and active avoidance conditioning with MILLER-MOWRER box.The main results were : (1) Hippocampal EEG during spontaneous behavior.Theta rhythms of 79 Hz were clearly observed during such behaviors as searching and rearing without locomotion and walking forward or around, as well as during head and body movements without locomotion. When animals were awake but motionless, hippocampal EEG consisted of desynchronized activity was also observed.(2) Hippocampal EEG during active avoidance learning.Hippocampal theta activity was not produced by the presentation of CS (2000 Hz pure tone) in habituation trials. In avoidance training, CS elicited a clear train of theta activity (79 Hz) starting a few seconds before the occurrence of avoidance responses. In the final state of avoidance learning, theta activity occurred immediately after the onset of CS and theta frequency increased to 911 Hz just before shuttling to the next compartment.From these and other results, hippocampal theta activity was shown to be associated not only with voluntary movement as suggested by VANDERWOLF but also with arousal level or general attention level.