Hippocampal theta activity in the acute precollicular rat

In eleven acute precollicular rats, cortical and hippocampal EEG activity was recorded. Hippocampal theta activity of low frequency (mean 4.5 c/sec) was found in nine rats and in four occupied above 50% of the recording time. In contrast, in the cortex the synchronized EEG activity dominated. The electrical stimulation of the posterior hypothalamus induced the theta rhythm, or increased its frequency. The large amounts of theta activity in some rats suggests that the forebrain theta pacemakers, partly modulated by the posterior hypothalamus, are released from brain stem inhibitory influences.