[Localization and gustatory responsiveness of cortical taste area in the hamster]

Mapping of evoked potentials on the cortical surface following electrical stimulation of the chorda tympani and the glossopharyngeal nerve, and anodal D.C. stimulation of the tongue indicated that the cortical taste area (CTA) was located in the dysgranular insular cortex just dorsal to the rhinal fissure near the middle cerebral artery in the hamster. Bilateral lesion of the CTA attenuated or disrupted the conditioned taste aversion that had been acquired preoperatively. This fact suggests that the CTA plays a role in some cognitive processes of taste. Experiments using anterograde and retrograde axonal transport of wheat-germ agglutinin conjugated horseradish peroxidase showed that the CTA received inputs from the contralateral CTA, amygdala, thalamic taste area and the pontine taste area, and that neurons in the CTA (chiefly in layer V) sent axons to the contralateral CTA, amygdala, and the thalamic, pontine and bulbar taste areas. Responses of 87 CTA neurons to the four basic taste stimuli were recorded in urethane-anesthetized hamsters. Majority of the CTA neurons (85%) existed in the dysgranular insular cortex. Neurons responding best to sucrose tended to be located rostrally, those to NaCl caudally, and those to HCl were distributed evenly in the CTA. Judging from the breadth of responses to the four tastes and across-neuron correlation coefficients, responsiveness of neurons in layer V is more narrowly tuned than in layers II-IV and VI.