Proper social behavior is learned through a process of social feedback from others, such as punishments and rewards. The striatum is important for feedback-based learning, as it is considered the...Show moreProper social behavior is learned through a process of social feedback from others, such as punishments and rewards. The striatum is important for feedback-based learning, as it is considered the reward center of the brain. This process could be dysfunctional in individuals exhibiting antisocial behavior, which could be explained by differences in striatum-activity after receiving social feedback. Non-clinically diagnosed participants (N=28, ages 18-30) were asked to fill out the Youth Psychopathic Traits Inventory (YPI) to determine their level of antisocial behavioral traits. During a Social Network Aggression Task (SNAT), the participants received positive, neutral, or negative feedback, accompanied by a picture of a peer on the participants’ profile, while in an MRI scanner to measure striatum activity. Participants could retaliate after feedback by sending noise blasts to their peer. No main effect of YPI scores on striatum activity was found, but only after adjusting for sex. No main effect of YPI scores on noise blast duration was found either. Female participants were found to potentially discriminate more between noise blast duration sent depending on the feedback valence received, compared to male participants. Our results do not support antisocial behavior being related to a defect in social reward-based learning in non-clinical individuals, but only after correcting for sex. Sex was found to be a confounding variable when analyzing antisocial behavior, which has not always been corrected in current literature.Show less
Reward processing abnormalities have been observed in individuals with attention deficit/hyperactivity disorder (ADHD) in both behavioral and neuroimaging studies. Models of reinforcement learning...Show moreReward processing abnormalities have been observed in individuals with attention deficit/hyperactivity disorder (ADHD) in both behavioral and neuroimaging studies. Models of reinforcement learning in healthy individuals have laid the foundation for neurobiological theories addressing reward processing in ADHD. In healthy individuals, dopamine responses in ventral striatum (VS) gradually shift from actual rewards received (prediction error [PE]), toward cues which reliably predict such rewards (reward expectancy [RE]). Drawing on these observations, two theories posit that either low striatal dopamine (dynamic developmental theory) or failed signal shifts per se (dopamine transfer deficit theory) are behind reward-processing deficits in individuals with ADHD. However, the predicted signal abnormalities have not been examined directly. Forty-two participants with ADHD and 56 typically developing (TD) controls participated in a functional magnetic resonance imaging (fMRI) reward paradigm examining whole-task and temporal-change measures of PE and RE. Results showed that, contrary to theoretical predictions, the groups did not differ in either an overall measure of RE, or a composite index of PE-RE signal shifts. Furthermore, while overall PE activity was higher in the ADHD group (partly supporting the dopamine transfer deficit theory, which allows for high PE), observed decreases over time were similar between the groups (which was unexpected). Exploratory dimensional analyses showed that while a positive linear relationship between hyperactive/impulsive symptoms and RE was present in the full group, a quadratic (inverse U-shape) model better explained this relation in a sub-sample with currently-diagnosed ADHD, possibly supporting a model of downregulation due to higher symptoms. Finally, there were no significant associations between the index of temporal signal shifts and symptoms, or between overall PE and symptoms. In sum, results do not support the dynamic developmental theory, and only partially support the dopamine transfer deficit theory. Additionally, results suggest that overall signals, rather than dynamic changes, are better able to differentiate ADHD whether at the group level (PE) or at the individual level (RE). Increased PE in ADHD also suggests that immediate rewards (versus delayed reward anticipation cues) may be a useful strategy for interventions.Show less
