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Social rewards are strong drivers of behavior and fundamental to well-being, yet there is a lack of consensus regarding what actually defines a reward as "social." Because a systematic overview of existing social reward operationalizations is currently absent, a review of the literature seems necessary to advance toward a unified framework and to better guide research and theory. To bridge this gap, we preregistered and conducted the first comprehensive systematic review of human and animal experimental studies that used the term "social reward" and charted existing operationalizations, revealing the implicit and explicit definitions used in the field. Stimulus characteristics and measures of social reward were extracted from a total of 384 studies encompassing 42,118 participants and subjects. We provide detailed summaries of these elements, stratified by species (human/animal) and study type (behavioral, brain imaging, pharmacological, and physiological). Two main aspects were found to account for most of the difference in operationalizations: the sensory richness of a stimulus (intimacy) and engagement in social interaction (i.e., the synchronous observation and action between at least two individuals, viz., immediacy). Drawing insights from second-person neuroscience approaches and theoretical models in the field of human-computer interaction, we propose that human and animal research can greatly benefit from considering these properties, as they have important theoretical and practical consequences for human and translational research, with far-reaching implications for neighboring research fields such as those pertaining to social media and the development of artificial intelligence. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Background: Atypical anticipation of social reward has been shown to lie at the core of the social challenges faced by individuals with autism spectrum disorder (ASD). However, previous research has yielded inconsistent results and has often overlooked crucial characteristics of stimuli. Here, we investigated ASD reward processing using social and nonsocial tangible stimuli, carefully matched on several key dimensions., Methods: We examined the anticipation and consumption of social (interpersonal touch) and nonsocial (flavored milk) rewards in 25 high-functioning individuals with ASD and 25 neurotypical adult individuals. In addition to subjective ratings of wanting and liking, we measured physical energetic expenditure to obtain the rewards, brain activity with neuroimaging, and facial reactions through electromyography on a trial-by-trial basis., Results: Participants with ASD did not exhibit reduced motivation for social or nonsocial rewards; their subjective ratings, motivated efforts, and facial reactions were comparable to those of neurotypical participants. However, anticipation of higher-value rewards increased neural activation in lateral parietal cortices, sensorimotor regions, and the orbitofrontal cortex. Moreover, participants with ASD exhibited hyperconnectivity between frontal medial regions and occipital regions and the thalamus., Conclusions: Individuals with ASD who experienced rewards with tangible characteristics, whether social or nonsocial, displayed typical subjective and objective motivational and hedonic responses. Notably, the observed hyperactivations in sensory and attentional nodes during anticipation suggest atypical sensory overprocessing of forthcoming rewards rather than decreased reward value. While these atypicalities may not have manifested in observable behavior here, they could impact real-life social interactions that require nuanced predictions, potentially leading to the misperception of reduced interest in rewarding social stimuli in ASD., (Copyright © 2024 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Facial mimicry is a ubiquitous social behaviour modulated by a range of social cues, including those related to reward value and self-relevance. However, previous research has typically focused on a single moderator at a time, and it remains unknown how moderators interact when studied together. We compared the influence of reward value and self-relevance, by conditioning participants to associate certain faces with winning or losing money for themselves, or, with winning or losing money for another person. After conditioning, participants watched videos of these faces making happy and angry facial expressions whilst we recorded facial electromyographic activity. We found greater smile mimicry (activation of the Zygomaticus Major muscle) in response to happy expressions performed by faces associated with participants' own outcomes vs. faces associated with another person's outcomes. In contrast to previous research, whether a face was associated with winning or losing money did not modulate facial mimicry responses. These results, although preliminary, suggest that when faces are associated with both self-relevance and reward value, self-relevance could supersede the impact of reward value during facial mimicry., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

The observation of animal orofacial and behavioral reactions has played a fundamental role in research on reward but is seldom assessed in humans. Healthy volunteers (N = 131) received 400 mg of the dopaminergic antagonist amisulpride, 50 mg of the opioidergic antagonist naltrexone, or placebo. Subjective ratings, physical effort, and facial reactions to matched primary social (affective touch) and nonsocial (food) rewards were assessed. Both drugs resulted in lower physical effort and greater negative facial reactions during reward anticipation, especially of food rewards. Only opioidergic manipulation through naltrexone led to a reduction in positive facial reactions to liked rewards during reward consumption. Subjective ratings of wanting and liking were not modulated by either drug. Results suggest that facial reactions during anticipated and experienced pleasure rely on partly different neurochemical systems, and also that the neurochemical bases for food and touch rewards are not identical., Competing Interests: SK, SG, CM, PS, IG, MW, CE, GS No competing interests declared, (© 2020, Korb et al.)

Whether cognitive, motivational and hedonic aspects of reward anticipation and consumption can be reliably assessed with explicit and implicit measures, and if different motivational (decision utility) and hedonic (experienced utility) processes get recruited by distinct reward types, remain partly unsolved questions that are relevant for theories of social and non-social decision-making. We investigated these topics using a novel experimental paradigm, including carefully matched social and nonsocial rewards, and by focusing on facial responses. Facial expressions are indeed an often-cited implicit measure of rewards' hedonic impact. For example, food rewards elicit powerful facial responses - characterized by lip smacking, tongue protrusion, and relaxation of the middle face - in human newborns, juvenile monkeys, and adult rats. The same stimuli elicit more nuanced facial reactions in adult humans, which can be best captured with facial electromyography (fEMG). However, little is known about facial expressions preceding reward consumption, reflecting the motivation to obtain and possibly the expected pleasantness of a reward, and whether similar facial expressions are elicited by different types of rewards. To investigate these questions, a novel within-subject experimental paradigm was developed. During the anticipation and consumption of social (affective touch) and nonsocial (food) rewards, explicit (ratings of wanting and liking, physical effort) and implicit (fEMG) measures of wanting and liking were taken in 43 healthy adult participants. Reduced activation of the Corrugator Supercilii (CS) muscle (reflecting less frowning and indicating greater positive response) was found in trials with higher wanting and effort during the anticipation of food rewards, as well as in trials with higher liking and effort during the consumption of food rewards. The CS muscle is thus a sensitive measure of wanting and liking of food rewards both during their anticipation and consumption. Crucially, thanks to careful reward matching, these results cannot be explained by differences in subjective wanting, liking, or effort produced to obtain the two types of rewards. No significant modulation of the Zygomaticus Major (ZM) muscle was found for social or food rewards. Explorative analyses however indicated that the ZM may activate during the delivery of the most wanted touch, but not for the most wanted food. The absence of significant effects of social rewards on the activation of CS and ZM muscles are discussed in relation to the specifics of this innovative task comparing two types of matched rewards in the same participants. The present findings contribute to the understanding of the processes underlying motivational and hedonic aspects of rewards, and may therefore inform models of social and non-social decision-making., (Copyright © 2019 Elsevier B.V. All rights reserved.)