Electrophysiological Responses to Bitter Stimuli in Primate Cortexa


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    This study was supported by research grant BNS-8514302 from the National Science Foundation.

Corresponding author: Thomas R. Scott, Department of Psychology, University of Delaware, Newark, DE 19716. Tel: (302)831-2436; fax: 302-831-3645; email: trscott@udel.edu


ABSTRACT: Studies investigating fine details of gustatory coding in the domain of each basic taste quality have been completed for sweet, salt, and sour stimuli. In the present experiment, we used chemicals that humans describe as predominantly bitter. We recorded the activity of 50 taste neurons in insular cortex of two cynomolgus macaques. Stimuli were water, fruit juice, glucose, NaCl, HCl, and 16 bitter solutions. In a multidimensional taste space the 16 bitter stimuli formed a coherent cluster composed of three main subgroups: (1) QHCl, phenylalanine, theophylline, caffeine, propyl-thiouracil (PROP), and phenylthiocarbamide (PTC), all of which humans describe as rather purely bitter, (2) MgCl2, CaCl2, NH4Cl, and arginine, which humans describe as salty-bitter, and (3) urea, cysteine, and vitamin B1, which are described as sour-bitter. Vitamin B2, histidine and nicotine were in the center of the bitter cluster. Human descriptions of taste qualities conformed well to the presumed quality of each stimulus as inferred from its position in the multidimensional space (MDS), reinforcing the use of the macaque as a neural model for human gustation.