EXPERIMENTAL HYPOGEUSIA FROM HORSLEY-CLARKE LESIONS OF THE THALAMUS IN MACACA MULATTA

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Abstract
Gustatory discriminatory capacity for quinine hydrochloride was detd. in 10 Macaca mulatta monkeys before and after bilateral electrolytic lesions of the thalamus. Taste was tested by the preference method. This involved measuring the relative amts. of water and of quinine soln. drunk by the animal when these liquids constituted the only available supply of fluid. The conc. of the quinine soln. was decreased on successive days and the amt. of quinine drunk at each conc. was expressed as a % of the total fluid intake. These figures were plotted against the conc. to yield threshold curves. The close agreement of independently repeated detns. established the reliability of the method. Bilateral lesions of the posteroventral thalamic nuclei produced marked disturbances in gustatory discrimination as evidenced by postoperative shifts of the threshold curves. Histological studies showed that the severity of the deficit was proportional to the extent of damage to the n. ventralis posteromedialis (arcuate n.). Anatomical studies indicate that this nucleus receives fibers from the secondary tri-geminal pathways and projects onto the face sensory area of the cortex. It was therefore suggested that taste fibers synapse in the thalamus in close association with fibers bearing somatosensory impulses from face, mouth, and tongue. The significance of the findings with respect to the cortical localization of taste was discussed.