The possible correlation of 4-12 Hz hippocampal field oscillations (theta rhythm) with motor and cognitive behavior was studied by recording the hippocampal electroencephalogram in non-locomoting rats as they solved a hippocampus-dependent place recognition task. The electroencephalogram (EEG) during the place recognition task was compared with the EEG during a control task, which had the same motor demands but did not require place recognition. In the place recognition task, the rat was passively transported on the periphery of a circular rotating arena, operant responses (lever pressing in Experiment 1 and licking in Experiment 2) emitted in a 60 degrees reward sector of the arena trajectory were reinforced. As expected the theta rhythm was observed during "voluntary" movements such as walking and lever pressing. During walking and lever pressing, when prominent theta was observed, the frequency increased within the first 10 min of a session. When the rats were not moving, during licking or staying motionless, both the theta amplitude and frequency were lower compared with the EEG during walking. There were no correlations between any theta characteristics and cognitive demand of the tasks.
(c) 2005 Wiley-Liss, Inc.