Item

Abstract

Phasic and tonic facets of dopamine release have been postulated as playing distinct roles inrepresenting respectively appetitive prediction errors that mediate learning, and average rates of reward thatmediate motivational vigour. However, empirical research has yet to provide evidence for the latter in a man-ner uncorrupted by influences of the former. We therefore designed a simple visual-search task in whichwe measured the force exerted when subjects reported the location of a target. In addition to a fixed rewardfor correct responses, subjects earned a performance-independent baseline monetary amount which variedacross blocks. To decorrelate an influence of baseline reward from a prediction error, we provided subjectsinformation at the start of each block regarding the amount they would receive in the subsequent block.Despite force not having any instrumental consequence, participants pressed harder for a larger baselinereward, consistent with the expression of a form of Pavlovian vigour. This larger baseline reward was asso-ciated with enhanced activity in dopamine-rich midbrain structures (ventral tegmental area/substantia nigrapars compacta; VTA/SN) to a degree that correlated across subjects with the strength of their behaviouralcoupling between reward and force. An opposite pattern was observed in subgenual cingulate cortex (sGC),a region involved in regulating negative emotional responses. These findings highlight a crucial role forVTA/SN and sGC in mediating an effect of average reward on tonic aspects of motivation.