'Liking' and 'wanting' food rewards: brain substrates and roles in eating disorders

Abstract

What brain reward systems mediate motivational 'wanting' and hedonic 'liking' for food rewards? And what roles do those systems play in eating disorders? This article surveys recent findings regarding brain mechanisms of hedonic 'liking', such as the existence of cubic-millimeter hedonic hotspots in nucleus accumbens and ventral pallidum for opioid amplification of sensory pleasure. It also considers brain 'wanting' or incentive salience systems important to appetite, such as mesolimbic dopamine systems and opioid motivation circuits that extend beyond the hedonic hotspots. Finally, it considers some potential ways in which 'wanting' and 'liking' might relate to eating disorders.

Fig.1

Unconscious induction of ‘liking’ and ‘wanting’ to drink a sweet beverage. Thirsty people were shown subliminally fast visual presentations of either happy facial expressions or angry facial expressions that were too brief to be consciously perceived but should still have activated brain mesolimbic circuits. Then they completed a cognitive task of identifying gender of a consciously seen face (to wipe away any conscious affect engendered by the faces) before being asked to rate their own hedonic mood or to evaluate a sweet citric fruit-flavored beverage, which they could pour and ingest as they wished. No changes in hedonic ratings of subjective mood were detected after subliminal faces, but people poured and drank roughly twice as much after subliminal happy faces than after subliminal angry faces. Modified from [18].

Fig. 2

Hedonic hotspots and hedonic circuits. Hedonic hotspots are shown in nucleus accumbens, ventral pallidum, and brainstem parabrachial nucleus where opioid or other signals cause amplification of core ‘liking’ reactions to sweetness. Reprinted by permission from [55], based on [38,76,80].

Fig. 3

Taste ‘liking’ reactions and contrast map of nucleus accumbens hotspots. Positive ‘liking’ reactions to pleasant sweet tastes shared by human newborn, young orangutan, and adult rat (tongue protrusion; left top), and aversive ‘disliking’ reactions to unpleasant bitter tastes (gape; left bottom). Opioid hotspots and coldspots in the nucleus accumbens (medial shell region shown in sagittal view; right). Green; the entire medial shell mediates opioid-stimulated increases in ‘wanting’ for food reward. Red; only a cubic-millimeter sized hedonic hotspot generates increases in ‘liking’ for the same opioid stimulation. Blue; opioid stimulation of a small hedonic ‘coldspot’ suppresses ‘liking’ reactions to sucrose, whereas a larger purple zone suppresses ‘disliking’ reactions to quinine, all while stimulating food intake. Reprinted by permission from [55], based on data from [53].

Fig. 4

Homology in affective facial expressions of taste ‘liking’: Left: Taxonomic tree based on shared details of affective facial expressions to taste. Behavioral expression taxonomy mirrors phylogenetic relationships among humans, 11 other primate species and rats. Species that are closely related share the most components (indicated by connecting horizontal lines). All species share some universal components, such as gapes to bitter. Right: Allometric deep structure in the timed duration of a single tongue protrusion. Although cycle durations of rodents are short whereas cycles of apes and humans are long, they all follow the identical timing rule that generates speed proportionally to body size. Modified from [42,43].

Fig. 5

Components of liking, wanting, and learning inside reward. This table represents the various components of reward discussed, and how each has been measured in experiments. The reward components occur together simultaneously, but have separable neural substrates and different psychological features. For example, ‘liking’ or core hedonic impact is generated by hedonic hotspot circuits in accumbens-pallidal-brainstem; ‘wanting’ or incentive salience depends heavily on mesolimbic dopamine projections to accumbens-striatum and related corticolimbic circuits, cognitive goal values of tasty rewards may involve orbitofrontal cortex, etc. Most reward components have both explicit (conscious) and implicit (unconscious) forms, which also can be measured in different ways and which may differ in neural substrates (e.g., cortical versus subcortical circuit weighting). Modified from [199].