The functional relationship between septal and hippocampal unit activity and hippocampal theta rhythm

Abstract

The correlation between septal and hippocampal unit activity and hippocampus EEG were studied in unanesthetized curarized rats. Extracellular recordings were statistically analyzed in order to obtain the time interval histograms and auto and crosscorrelograms. During the induction of a hippocampal theta rhythm by sensory stimulation or physostigmine injection the septal units showed a bimodal time interval histogram. The autocorrelograms of septal and hippocampal unit activity and the crosscorrelograms between units and from them with the hippocampal EEG showed 4–6 waves of decreasing amplitude in one second interval. The autocorrelograms showed serial dependence. LSD-25 abolished the hippocampal rhythmic activity. During the control period as well as after LSD-25 treatment in physostigmine injected animals there was a significantly smaller number of spikes in each septal burst. Scopolamine and pentobarbitone disorganized septal and hippocampal activity.