No abstract

Whether positive mood can change reinforcement learning or not remains an open question. In this study, we used a probabilistic learning task and explored whether positive mood could alter the way positive versus negative feedback was used to guide learning. This process was characterized both at the behavioral and electro-encephalographic levels. Thirty two participants were randomly allocated either to a positive or a neutral (control) mood condition. Behavioral results showed that while learning performance was balanced between the two groups, participants in the positive mood group had a higher learning rate than participants in the neutral mood group. At the electrophysiological level, we found that positive mood increased the errorrelated negativity when the stimulus-response associations were deterministic, selectively (as opposed to random or probabilistic). However, it did not influence the feedback-related negativity. These new findings are discussed in terms of an enhanced internal reward prediction error signal after the induction of positive mood when the probability of getting a reward is high.

Goal adaptive behavior requires the rapid detection of conflicts between actions and intentions or goals.While many studies have focused in the past on the influence of negative affect on this cognitive control process (and more specifically, on error monitoring), little is known about possible modulatory effects of positive affect on it. To address this question, we used a standard (positive) mood induction procedure (based on guided imagery) and asked participants to carry out a speeded Go/NoGo task, while high density EEG was recorded concurrently. As a control condition, we used a group with neutral mood. ERP results showed that the ERN (error-related negativity) component, reflecting early error detection within the dorsal anterior cingulate cortex, was not influenced by happy mood. In contrast, the subsequent Pe (error positivity) component, related to the appraisal of the motivational significance of errors, was reliably smaller in the happy relative to the neutral mood group. Complementing source localization analyses showed that this effect was explained by a decreased activation within the posterior cingulate and insular cortices. These results were obtained in the absence of group differences regarding behavioral performance and tonic arousal. These findings suggest that happy mood likely decreases and changes the motivational significance of worse than expected events (Pe), while leaving their earlier automatic detection (ERN) unaltered. We discuss these new results in terms of dynamic changes in the complex interplay of performance monitoring with motivation.

Collectively, these results lend support to the assumption that MDD does not impair reward processing per se during RL. Instead, it seems to alter the processing of the emotional value of (external) reinforcers during RL, when additional intrinsic motivational processes have to be engaged.

Major depression is characterized by abnormal reward processing and reinforcement learning (RL). This impairment might stem from deficient motivation processes, in addition to reduced reward sensitivity. In this study, we recorded 64-channel EEG in a large cohort of major depressive disorder (MDD) patients and matched healthy controls (HC) while they performed a standard RL task. Participants were asked to discover, by trial and error, several hidden stimulus-response associations having different reward probabilities, as enforced using evaluative feedback. We extracted induced fronto-midline Theta (FMT) power timelocked to the response and feedback as neurophysiological index of RL. Furthermore, we assessed approach-related motivation by measuring frontal alpha asymmetry concurrently. At the behavioral level, MDD patients and HCs showed comparable RL. At the EEG level, FMT power systematically varied as a function of reward probability, with opposing effects found at the response and feedback levels. Although this global pattern was spared in MDD, at the feedback level these patients showed however a steep FMT power decrease across trials when reward probability was low. Moreover, they showed impaired approach-related motivation during task execution, as reflected by frontal Alpha asymmetry. These results suggest a dissociation between (globally spared) RL and (impaired) approach motivation in MDD.