Taste stimuli, hedonic

Recent evidence suggests that the oral detection of fatty acids such as stearic acid do occur in the human and rodent oral cavity, and stimulate a fatty acid taste response. Both animal and human studies indicate that stearic acid elicits a small to moderate taste response in the oral cavity. The hedonic appeal of fats may be enhanced especially when consumed with carbohydrates. Future studies will determine whether long-chain fatty acids such as stearic acid or linoleic acid represent a primary taste stimulus in the human oral cavity. Finally, improved dehvery methods for saturated and unsaturated fatty acids for psychophysical studies will stimulate the advancement of this important field of study. 

Summing up, impairment of DA transmission by DA receptor antagonists and in particular by D1 receptor antagonists impairs the acquisition of place preference conditioned by nondrug rewards (food, water, sucrose and sex). This effect is unrelated to an impairment of the hedonic impact of the rewards, consistent with other evidence, obtained from taste reactivity and consumption studies, that DA is not involved in stimulus-bound hedonia. Therefore, conditioned place-preference studies utilizing conventional rewards support a role of DA in Pavlovian incentive learning. 

Novelty being a prerequisite for the stimulation of DA release in the NAc shell but not for behavioral hedonic reactions, release of DA in this area is likely to be a consequence rather than the cause of the appetitive properties of taste stimuli, consistent with the idea that taste-hedonia does not depend on DA (Berridge and Robinson, 1998). These observations, however, leave open the issue of a role of DA in state-hedonia (euphoria, eutimia) as distinct from stimulus-bound (e.g. taste) hedonia. 

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