The responsiveness of neurons in the insular gustatory cortex of the macaque monkey is independent of hunger.

ABSTRACT

(1) In order to determine whether the responsiveness of neurons in the insular gustatory cortex is influenced by hunger, neuronal activity was analysed in it while macaque monkeys (Macaca fascicularis) were fed to satiety. The responses of single neurons in the insular gustatory cortex to the protypical taste stimuli glucose, NaCl, HCl and quinine HCl, and to fruit juice, were measured before, while, and after the monkey was fed to satiety with glucose or fruit juice. (2) While behavior turned from avid acceptance to active rejection upon repletion, the responsiveness of the neurons to the stimulus array, including the satiating solution, was unmodified. (3) It is concluded that in the insular gustatory cortex, neuronal responses to gustatory stimuli are not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurons recorded in the hypothalamus, which only respond to the taste of food when the monkey is hungry. Thus the neurons in the insular gustatory cortex are involved in a motivation-independent analysis of gustatory stimuli, whereas the hypothalamic neurons may be more closely related to the influence of motivational state on behavioral responsiveness to gustatory stimuli.