Increased orientation to sensory stimuli following medial hypothalamic damage in rats.

After unilateral medial hypothalamic damage, rats become hyperresponsive to touch, odors, and visual stimuli presented on the side contralateral to the damage, while responding to ipsilateral stimuli remains near preoperative levels. These rats would orient their snouts more precisely to stimuli presented on the contralateral side, turn toward touch of more caudal points along that body surface, and pursue moving stimuli more vigorously on that side. Rats with unilateral damage would also viciously bite relatively weak noxious stimuli presented on the contralateral side. After injections of amphetamine, rats turned away from the side of the damage. After bilateral damage, rats showed increased responsiveness to sensory stimuli arising on either side. The rats with unilateral damage began eating more food from a container located in the contralateral sensory field than they had preoperatively. In addition, they began to attack mice more frequently and with shorter latencies when the mouse was on the side contralateral to the lesion. Just as the sensory loss after lateral hypothalamic damage contributes to the aphagia and decreased aggressive behavior of such rats, it seems that increased responsiveness to sensory stimuli plays a role in the syndrome of hyperphagia, finickiness, and increased aggressiveness seen after medial hypothalamic damage.