Characterizing the role of movement in ventromedial striatal dopamine signals related to reward

Although the dopamine system’s involvement in both action control and conveying reward-related information, it is understudied how these two functions are integrated. Using a rewarded go/no-go paradigm to examine the integration of these functions, a previous study demonstrated that self-initiated actions influence reward-related dopamine release in the striatum. We expanded this work by comparing self- and signal-initiated actions, since dopamine is strongly recruited by environmental signals. Furthermore, some studies define action requirements for ‘no-go’ trials as immobility, others as withholding ‘go’ responses. Therefore, using fast-scan cyclic voltammetry in the ventromedial striatum, we investigated dopamine release in a rat go/no-go task (with either self- and signal-initiated trials), where auditory cues prompted action requirements to earn food rewards: lever press (‘go’), immobility (‘no-go’), or withholding the aforementioned actions and immediately approaching the food magazine (‘free’). Dopamine release was largest and peaked earliest in ‘free’-reward trials but was smallest and peaked later in ‘no-go’ trials, emphasizing the importance of true no-go trials. The difference in peak latencies suggests encoding of reward proximity, whereas magnitude differences was inversely related to effort requirements. Replicating previous findings, we show that during self-initiated trials, dopamine release is contingent on both reward prediction and action initiation. However, this effect was absent when the trial-start was externally signaled. Overall, during self-initiated actions, action control and reward-related information govern dopamine interactively, whereas these two functions are separated during signal-initiated actions, indicating that the interactive effect is dependent on internal motivation.