Two types of aphagia and two types of sensorimotor impairment after lateral hypothalamic lesions: observations in normal weight, dieted, and fattened rats.

Abstract

In two experiments, reactions to food and to tactile stimuli were examined in rats whose body weights were normal, reduced by restricted feeding (dieted), or raised by having access to palatable foods (fattened) prior to receiving bilateral lesions in the lateral hypothalamic (LH) area. Postoperative aphagia and sensorimotor impairments were less prolonged than normal in the dieted rats and more prolonged than normal in the fattened rats. The LH lesions produced a transient hyperthermia which was attenuated by dieting and facilitated by fattening. Certain motor impairments (which accompanied more posterior lesion placements), hypokinesia, and a lesion-induced exaggerated aphagia to novel foods were relatively unaffected by preoperative body weight. Depending importantly upon lesion placement, there appeared to be at least two types of aphagia and two types of sensorimotor impairment. Animals with more posterior LH lesions displayed a passive kind of aphagia and sensory neglect. These animals did not react to food or to sensory stimuli presented externally, but they chewed and appeared to swallow food placed in the mouth. Animals with more anterior LH lesions displayed an active kind of aphagia and sensory rejection. These latter animals briskly turned their heads toward food or a light touch; however, they also showed simple stereotyped withdrawal or reactions of aversion to the food, to a light touch, and to a variety of sensory stimuli. Animals with intermediately placed lesions showed symptoms common to passive and active aphagia and to sensory neglect and sensory rejection. The effects of preoperative weight manipulation on the specific types of aphagia and sensorimotor impairments are discussed.