Quantitative analysis of hippocampal rhythmical slow activity induced by stimulation of different diencephalic structures

Abstract

Electrical stimulation was applied to freely moving rats with various current intensities and frequencies, via electrodes implanted in the nucleus dorsomedialis hypothalami (pars dorsalis), medial forebrain bundle, and zona incerta, while concurrent hippocampal electroencephalogram and behavior were recorded. Rewarding stimulation of the dorsomedial hypothalamus, with frequencies from 50 to 150 c/s and intensities from 25 to 100 μA, elicited in both ipsilateral and contralateral hippocampal electroencephalogram records a pronounced rhythmical slow activity with frequencies ranging from 8 to 12 Hz. Rewarding stimulation of medial forebrain bundle and aversive stimulation of zona incerta, with identical current intensity and frequency, were accompanied by rhythmical slow activity with maximum frequencies of 7–8 Hz. This 7–8 Hz activity was found to be identical to rhythmical slow activity produced during exploratory behavior. These results are discussed with respect to hippocampal afferents involved in the two types of rhythmical slow activity.