Head movements elicited by electrical stimulation of the anteromedial cortex of the rat

Abstract

Electrical stimulation, 5-sec trains, 0.5 msec rectangular pulses, 20 Hz pulse frequency, was applied to the anteromedial cortex of awake rats (N=28) to determine if head orienting behavior could be elicited. Following recovery from surgery in which up to six monopolar electrodes were implanted, the rats were adapted to and tested on a small platform surrounded by water. Elicited behavior patterns reliable at 150 μA or less in Experiment 1 (66 sites) and at 100 μA or less in Experiment 2 (32 sites) were analyzed. The most common response was a single head turn in a direction contralateral to the side of stimulation. Positive sites occurred throughout the anterior cingulate and the medial precentral regions. Coordinated forelimb movements were associated with contralateral head movements at dorsal anterior cingulate sites. Ipsilateral head turns were elicited at sites in the most rostral and ventral parts of the anteromedial cortex, including the prelimbic area. Lateral scanning sites were widespread but tended to concentrate at the mergence of the contralateral and ipsilateral movement fields. Vertical movements were often elicited with ipsilateral movements; dorsal sites supported downward head movements and ventral sites supported upward head movements. Sites supporting forward head movements were concentrated in the anterior cingulate region caudal to the genu of the corpus callosum. Neck extension usually appeared in conjunction with lateral head movements and frequently with forelimb movements.