Dynamic computation of incentive salience: "wanting" what was never "liked".

Pavlovian cues for rewards become endowed with incentive salience, guiding "wanting" to their learned reward. Usually, cues are "wanted" only if their rewards have ever been "liked," but here we show that mesocorticolimbic systems can recompute "wanting" de novo by integrating novel physiological signals with a cue's preexisting associations to an outcome that lacked hedonic value. That is, a cue's incentive salience can be recomputed adaptively. We demonstrate that this recomputation is encoded in neural signals coursing through the ventral pallidum. Ventral pallidum neurons do not ordinarily fire vigorously to a cue that predicts the previously "disliked" taste of intense salt, although they do fire to a cue that predicts the taste of previously "liked" sucrose. Yet we show that neural firing rises dramatically to the salt cue immediately and selectively when that cue is encountered in a never-before-experienced state of physiological salt depletion. Crucially, robust neural firing to the salt cue occurred the first time it was encountered in the new depletion state (in cue-only extinction trials), even before its associated intense saltiness has ever been tasted as positively "liked" (salt taste had always been "disliked" before). The amplification of incentive salience did not require additional learning about the cue or the newly positive salt taste. Thus dynamic recomputation of cue-triggered "wanting" signals can occur in real time at the moment of cue re-encounter by combining previously learned Pavlovian associations with novel physiological information about a current state of specific appetite.