Neural correlates of reward-related response tendencies in an equiprobable Go/NoGo task.

Previous research has shown that motivational signals bias action over inaction, which may be due to putative inherent valence-action mappings, similar to those observed in the emotional domain. In the present functional magnetic resonance imaging (fMRI) study we sought to investigate the neural underpinnings of such reward-related response tendencies, and in particular, how valence-action compatibility effects arising from predominant response tendencies are reflected at the neural level, and whether overlapping emotional valence amplifies these effects. To this end, we employed an equiprobable (50:50) Go/NoGo task in which reward (reward/no-reward) and response mode (Go/NoGo) were signaled by orthogonal features of number targets that were overlaid on emotional images (positive, neutral, negative). Reward-related targets led to response facilitation (faster Go responses) and impairment in withholding responses (more NoGo commission errors), consistent with a reward-induced action bias. This pattern was paralleled by modulations in the left dorsolateral prefrontal cortex (dlPFC), with increased activity in no-reward as compared to reward-related Go trials, and the reversed pattern in NoGo trials. Albeit being processed in ventral visual areas, emotional background did not modulate performance in the present task, suggesting that irrelevant emotional information is globally outweighed by reward. In the current paradigm, which neither favors Go responses generally nor allows for differential preparation in Go versus NoGo trials, reward-related targets promote action over inaction. In turn, additional effort is needed to inhibit responses to these targets as well as to initiate responses to (less salient) no-reward targets, which may be considered as a downside of direct stimulus-reward associations.