Periodic behavioral changes during hippocampal theta rhythm elicited by septal stimulation in rats

The influence of an electrical stimulation of the medial septum on the electroencephologram of the dorsal hippocampus and behavior was studied in freely moving rats. A short stimulation at 4–12 Hz frequency always induced orienting behavior (searching, rearing, sniffing, exploration) as soon as hippocampal rhythmic slow activity, or theta rhythm is elicited. An increase in stimulation intensity or in pulse duration led to an increased occurrence of theta rhythm and likewise, to an increase of orienting behavior. Both the theta rhythm and orienting behavior were dependent on the stimulation frequency.During long-lasting septal stimulation at 7 Hz, which elicited a continuous hippocampal theta rhythm, periodic behavioral changes were observed, consisting of orienting behavior alternating with grooming behavior (cleaning, washing, licking, scratching). These rhythmic periods lasted for 3–5 min.The significance of the rhythmic behavioral changes are discussed in relation to the activity of the cholinergic septohippocampal system and to rapid-eye-movement sleep and memory consolidation.