FOOD REWARD - BRAIN SUBSTRATES OF WANTING AND LIKING

What are the neural substrates of food reward? Are reward and pleasure identical? Can taste pleasure be assessed in animals? Is reward neces sarily conscious? These questions have re-emerged in recent years, and there is now sufficient evidence to prompt re-examination of many pre conceptions concerning reward and its relation to brain systems. This paper reviews evidence from many sources regarding both the psychologi cal structure of food reward and the neural systems that mediate it. S pecial attention is paid to recent evidence from ''taste reactivity'' studies of affective reactions to food. I argue that this evidence sug gests the following surprising possibilities regarding the functional components and brain substrates of food reward. (1) Reward contains di stinguishable psychological or functional components-''liking'' (pleas ure/palatability) and ''wanting'' (appetite/incentive motivation). The se can be manipulated and measured separately. (2) Liking and wanting have separable neural substrates. Mediation of liking related to food reward involves neurotransmitter systems such as opioid and GABA/benzo diazepine systems, and anatomical structures such as ventral pallidum and brainstem primary gustatory relays. Mediation of wanting related t o food reward involves mesotelencephalic dopamine systems, and divisio ns of nucleus accumbens and amygdala. Both liking and wanting arise fr om vastly distributed neural systems, but the two systems are separabl e. (3) Neural processing of food reward is not confined to the limbic forebrain. Aspects of food reward begin to be processed in the brainst em. A neural manipulation can enhance reward or produce aversion but n o single lesion or transection is likely abolish all properties of foo d reward. (4) Both wanting and liking can exist without subjective awa reness. Conscious experience can distort or blur the underlying reward processes that gave rise to it. Subjective reports may contain false assessments of underlying processes, or even fail at all to register i mportant reward processes. The core processes of liking and wanting th at constitute reward are distinct from the subjective report or consci ous awareness of those processes.