Effects of brain lesions and atropine on hippocampal and neocortical electroencephalograms in the rat

Abstract

The relation between neocortical and hippocampal electroencephalogram (EEG) activity and behavior was studied in rats with forebrain and brain stem lesions. Atropine-sensitive neocortical low-voltage, fast activity (LVFA) recorded during immobility could be transiently abolished by lateral hypothalamic lesions. Atropine-sensitive hippocampal rhythmical slow activity (RSA) was produced by all brain stem lesions and became the dominant hippocampal EEG pattern in the alert immobile rat after medial pons lesions. Atropine-resistant LVFA and RSA normally associated with movement could be transiently abolished by lateral hypothalamic and orbital frontal lesions. In addition, lateral hypothalamic lesions produced an acute reduction in RSA frequency, during walking and swimming, of 1 to 4 Hz which lasted 1 to 15 days, and a chronic reduction of about 1 Hz. Lesions in the medial frontal neocortex, caudate putamen, medial hypothalamic nuclei, substantia nigra, raphé nuclei, lateral pons, caudal reticular formation, and locus ceruleus produced only slight transient or no change in atropine-resistant neocortical or hippocampal EEG activity. Motor and regulatory deficits could be produced by lesions which disrupted EEG as well as those which did not (i.e., lateral hypothalamus vs substantia nigra). The results support the suggestion that there are two types of LVFA and RSA, one of which is cholinergic, and further suggest that forebrain EEG activity may be related to the higher order control and activation of movement.