Alimentary responses to forebrain stimulation in monkeys.

Abstract

Electrical stimulation of 5885 loci in the forebrains of 15 male rhesus monkeys (M. mulatta) elicited the alimentary responses of food intake, water intake, food ejection, and vomiting. Intake of non-food objects was also recorded. The following results were obtained. Food intake was evoked from preoptic region, substantia innominata, lateral, dorsal and posterior hypothalamus, tegmentum, medial hypothalamus, midline thalamus, central grey, anterior internal capsule, putamen, and stria terminalis. Non-food intake was evoked from most of these structures and, additionally, from the anterior cingulate region. Water intake was elicited from the anterior cingulate region, anterior internal capsule, putamen, substantia innominata, lateral, dorsal and posterior hypothalamus, tegmentum, substantia nigra and medial hypothalamus. Food ejection and vomiting were obtained from the preoptic region and medial hypothalamus (ejection only), olfactory tubercle, amygdala, septum, fornix, and nucleus ventralis anterior. Quantitative measures of response probability, response distribution and threshold as well as behavioral analysis indicated that no simple anatomical or behavioral scheme could satisfactorily organize these data. Alimentary mechanisms appear to be diverse, nonunitary, and complex. Major contributions to all alimentary responses were obtained from extrahypothalamic tissue. Especially well documented were the relationship between the anterior cingulate gyrus and drinking and the nuc. ventralis anterior and vomiting. The putamen also contributed consistently to all alimentary responses. Within the hypothalamus, alimentary responses were elicited from the paraventricular zone but not from the ventromedial nucleus proper. The lateral hypothalamus, although an effective locus for evoked feeding, was not the most effective zone as measured by response probability, distribution, and threshold. A new scheme of organization of alimentary mechanisms is proposed which accounts for the increased anatomical and behavioral complexity documented in this study.