Everyday goals and experiences are often shared with others who may hold different places within our social networks. We investigated whether the experience of sharing a reward differs with respect to social network. Twenty human participants played a card guessing game for shared monetary outcomes with three partners: a computer, a confederate (out-of-network), and a friend (in-network). Participants subjectively rated the experience of sharing a reward more positively with their friend than the other partners. Neuroimaging results support participants’ subjective reports, as ventral striatal BOLD responses were more robust when sharing monetary gains with a friend, as compared to with the confederate or computer, suggesting a higher value for sharing with an in-network partner. Interestingly, ratings of social closeness co-varied with this activity, resulting in a significant partner × closeness interaction: exploratory analysis showed that only participants reporting higher levels of closeness demonstrated partner-related differences in striatal BOLD response. These results suggest that reward valuation in social contexts is sensitive to distinctions of social network, such that sharing positive experiences with in-network others may carry higher value.
The Pavlovian-to-instrumental transfer (PIT) paradigm probes the influence of Pavlovian cues over instrumentally learned behavior. The paradigm has been used extensively to probe basic cognitive and motivational processes in studies of animal learning but, more recently, PIT and its underlying neural basis have been extended to investigations in humans. These initial neuroimaging studies of PIT have focused on the influence of appetitively conditioned stimuli on instrumental responses maintained by positive reinforcement, and highlight the involvement of the striatum. In the current study, we sought to understand the neural correlates of PIT in an aversive Pavlovian learning situation when instrumental responding was maintained through negative reinforcement. Participants exhibited specific PIT, wherein selective increases in instrumental responding to conditioned stimuli occurred when the stimulus signaled a specific aversive outcome whose omission negatively reinforced the instrumental response. Additionally, a general PIT effect was observed such that when a stimulus was associated with a different aversive outcome than was used to negatively reinforce instrumental behavior, the presence of that stimulus caused a non-selective increase in overall instrumental responding. Both specific and general PIT behavioral effects correlated with increased activation in corticostriatal circuitry, particularly in the striatum, a region involved in cognitive and motivational processes. These results suggest that avoidance-based PIT utilizes a similar neural mechanism to that seen with PIT in an appetitive context, which has implications for understanding mechanisms of drug-seeking behavior during addiction and relapse.
The human striatum has been previously implicated in the processing of positive reinforcement, but less is known about its role in processing negative reinforcement. In this experiment, participants learn specific approach or avoid responses, mediated by positive and negative reinforcers respectively, to investigate how affective learning and associated neural activity are influenced by the motivational context in which learning occurs. The paradigm was divided into two discrete sessions, where participants could either earn monetary rewards (Approach sessions) or avoid monetary losses (Avoid sessions) based on successful learning. Specifically, a conditioned cue predicted the chance to win or avoid losing money contingent on a correct button press (Pre-learning trials), which upon learning led to the delivery of rewards or termination of losses (post-learning trials). Skin conductance responses (SCRs) and subjective ratings confirmed a learning effect (greater SCRs pre vs. post-learning) irrespective of reinforcer valence. Concurrently, activity in the ventral striatum was characterized by a similar learning effect, with greater responses during pre-learning. Interestingly, such learning effect was enhanced in the presence of a negative reinforcer, as suggested by an interaction between learning phase and session, highlighting the influence negative reinforcers can have on striatal circuits involved in learning and motivated behavior.
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