A search for the cortical gustatory area in the hamster

The gustatory area was searched in the cerebral cortex of the hamster by means of a combined approach using electrophysiological, behavioral, and histological experiments. The chorda tympani (CT), which innervates taste buds on the anterior part of the tongue, projected to a confined area anterior to the middle cerebral artery and just dorsal to the rhinal fissure. The trigeminal component of the lingual nerve (LN) area was located anterodorsal to the CT area, and the glossopharyngeal nerve (GN), which innervates taste buds on the posterior part of the tongue, was posterior to the CT area. The center of the CT and GN areas belonged to the dorsal part of the dysgranular insular cortex, and the LN area was within the primary somatosensory granular cortex. Bilateral symmetrical ablations of the CT and GN areas abolished the conditioned taste aversion (to sodium saccharin) that had been acquired before ablations, indicating a role of these areas in some cognitive processes of taste perception. Injections of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) in the CT and GN areas, centered in the dysgranular insular cortex, revealed that this cortical region had major fiber connections with the contralateral homotypical cortical area, ipsilateral amygdala (central, lateral and basolateral nuclei), ipsilateral parvicellular part of the posteromedial ventral nucleus of the thalamus, bilateral parabrachial nucleus, contralateral nucleus of the solitary tract, raphe nuclei, and the locus ceruleus. Conversely, injections of WGA-HRP in these target areas showed anterograde and/or retrograde transport in the similar dysgranular insular cortex and additionally in the ventral part of the granular insular cortex. The present results suggest that the cortical gustatory area of the hamster is about 1.5 X 1.5 mm in size with the topographic organization between anterior and posterior parts of the tongue, and is located mainly in the dysgranular insular cortex around the middle cerebral artery.