Diencephalic neuronal activity during acquisition and ingestion of food in sheep

Single unit recordings were made in the lateral hypothalamic region and ventrobasal thalamus in conscious sheep during presentation of food and feeding. Unit responses to all aspects of testing were observed between the two areas. However, analysis of the data revealed a functional division of unit types between the two regions. Unit responses specific to the sight of food, to the approach of food to the mouth, and during ingestion of food were observed in the lateral hypothalamic area, but not the ventrobasal thalamus. These responses were not associated with specific or generalized movements, non-specific arousal, with olfactory stimulation, or with other oral stimuli. Units responding in association with specific mouth movements or somatosensory stimulation of the face or mouth-parts were observed in the ventrobasal thalamus but not in the lateral hypothalamic area. In the case of movement-related activity, the response was independent of the stimulus inducing the movement, food and non-food stimuli being equally effective. This was also true of the somatosensory responses observed. Two possibilities in relation to this functional division are discussed. Firstly, that the ventrobasal thalamus receives oral sensory afferents which may be associated with the thalamic area for taste. Secondly, that the activity of hypothalamic cells recorded in the sheep is consistent with a role for this area of the brain in the guidance and control of ingestive behaviour in ruminant as well as non-ruminant species.