Determinants of taste preference and acceptability: quality versus hedonics

Abstract

Several methods exist for reliably determining the motivational valence of a taste stimulus in animals, but few to determine its perceptual quality independent of its apparent affective properties. Individual differences in taste preference and acceptability could result from variance in the perceptual qualities of the stimulus leading to different hedonic evaluations. Alternatively, taste perception might be identical across subjects, but the processing of the sensory signals in reward circuits could differ. Using an operant-based taste cue discrimination/generalization task involving a gustometer, we trained male Long-Evans rats to report the degree to which a test stimulus resembled the taste quality of either sucrose or quinine regardless of its intensity. The rats, grouped by a characteristic bimodal phenotypic difference in their preference for sucralose, treated this artificial sweetener as qualitatively different-compared to sucralose-avoiding rats, the sucralose-preferring rats found the stimulus much more perceptually similar to sucrose. Although the possibility that stimulus palatability may have served as a discriminative cue cannot entirely be ruled out, the profile of results suggests otherwise. Subsequent brief-access licking tests revealed that affective licking responses of the same sucralose-avoiding and -preferring rats differed across concentration in a manner approximately similar to that found in the stimulus generalization task. Thus, the perceived taste quality of sucralose alone may be sufficient to drive the observed behavioral avoidance of the compound. By virtue of its potential ability to dissociate the sensory and motivational consequences of a given experimental manipulation on taste-related behavior, this approach could be interpretively valuable.

Figure 1.

Mean (±SEM) Sucrose Generalization Scores for SA and SP rats in response to increasing concentrations of sucralose used as a test stimulus. A score of 0.0 indicates that responding to the test stimulus was identical to responding for 1.0 mm quinine; a score of 1.0 indicates that responding to the test stimulus was identical to responding for 600 mm sucrose. All rats, regardless of sucralose preference phenotype, treated water and the three lowest concentrations of sucralose as sharing a perceptual quality similar to that of 1.0 mm quinine. As the concentration of sucralose was increased beyond 2.5 mm, mean responding by SP and SA rats began to separate, with SP rats reporting that the salient taste quality associated with sucralose was similar to that of 600 mm sucrose, whereas SA displayed a pattern of responses indicative of sucralose sharing perceptual qualities of both 600 mm sucrose and 1.0 mm quinine. *SP rats greater than SA rats, ps < 0.05.

Figure 2.

Mean Sucrose Generalization Scores for SA and SP rats in response to RO water and a number of electrolyte-containing stimuli. Filled circles denote the Sucrose Generalization Score for each individual rat. A score of 0.0 indicates that responding to the test stimulus was identical to responding for 1.0 mm quinine; a score of 1.0 indicates that responding to the test stimulus was identical to responding for 600 mm sucrose. No differences between SP and SA rats were detected in response to any stimulus; as such, the data were collapsed across groups for further analyses (indicated by brackets). As the amount of dissolved electrolytes was increased, the mean Sucrose Generalization Scores displayed a tendency to approach a score of 0.5. One-sample t tests revealed that RO H₂O was not treated as significantly different from 1.0 mm quinine (bracket a), while Dasani bottled water, artificial (Art.) saliva, and 100 mm NaCl) were treated as significantly different from 1.0 mm quinine (ps ≤ 0.05; bracket b).

Figure 3.

Mean (±SEM) taste/water ratio of water-deprived SA and SP rats in response to increasing concentrations of sucralose presented in random order during brief-access tests in the Davis rig. A score of 1.0 indicates that the mean licking response to that concentration of sucralose was equal to the overall mean licking response to water. In agreement with Experiment 1, all rats treated the three lowest concentrations of sucralose as similar to water. By the 2.5 mm concentration, SP rats increased licking and SA rats decreased licking in response to increasing concentrations of sucralose. *SP rats greater than SA rats, ps ≤ 0.01.

Figure 4.

Mean (±SEM) lick score of need-free SA and SP rats in response to increasing concentrations of sucralose presented in random order during brief-access tests in the Davis rig. Scores >0.0 indicate that the animals licked more to sucralose relative to water; scores <0.0 indicate that the animals licked more to water relative to sucralose. Comparable to Figure 3, SA and SP rats treated the two lowest concentrations of sucralose as similar to water. Interestingly, in a water-replete state, SA and SP rats displayed reliable differences in their licking response at a 1 log unit lower concentration of sucralose (0.25 mm) compared with the fluid-deprived state (2.5 mm). *SP rats greater than SA rats, ps < 0.05.