Understanding the roots of prosocial behavior is an interdisciplinary research endeavor that has generated an abundance of empirical data across many disciplines. This review integrates research findings from different fields into a novel theoretical framework that can account for when prosocial behavior is likely to occur. Specifically, we propose that the motivation to cooperate (or not), generated by the reward system in the brain (extending from the striatum to the ventromedial prefrontal cortex), is modulated by two neural networks: a cognitive control system (centered on the lateral prefrontal cortex) that processes extrinsic cooperative incentives, and/or a social cognition system (including the temporo-parietal junction, the medial prefrontal cortex and the amygdala) that processes trust and/or threat signals. The independent modulatory influence of incentives and trust on the decision to cooperate is substantiated by a growing body of neuroimaging data and reconciles the apparent paradox between economic versus social rationality in the literature, suggesting that we are in fact wired for both. Furthermore, the theoretical framework can account for substantial behavioral heterogeneity in prosocial behavior. Based on the existing data, we postulate that self-regarding individuals (who are more likely to adopt an economically rational strategy) are more responsive to extrinsic cooperative incentives and therefore rely relatively more on cognitive control to make (un)cooperative decisions, whereas other-regarding individuals (who are more likely to adopt a socially rational strategy) are more sensitive to trust signals to avoid betrayal and recruit relatively more brain activity in the social cognition system. Several additional hypotheses with respect to the neural roots of social preferences are derived from the model and suggested for future research.

Purpose: To examine the T 2 -normal appearing spinal cord of patients with multiple sclerosis (MS) using diffusion tensor imaging. Materials and Methods:Diffusion tensor images of the spinal cord were acquired from 21 healthy subjects, 11 MS patients with spinal cord lesions, and 10 MS patients without spinal cord lesions on the T 2 -weighted MR images. Different diffusion measures were evaluated using both a region of interest (ROI) -based and a diffusion tensor tractography-based segmentation approach.Results: It was observed that the FA, the transverse diffusivity Ќ , and the ratio of the longitudinal and transverse diffusivities ( / Ќ ) were significantly lower in the spinal cord of MS patients with spinal cord lesions compared with the control subjects using both the ROI method (P ϭ 0.014, P ϭ 0.028, and P ϭ 0.039, respectively) and the tractography-based approach (P ϭ 0.006, P ϭ 0.037, and P ϭ 0.012, respectively). For both image analysis methods, the FA and the / Ќ values were significantly different between the control group and the MS patient group without T 2 spinal cord lesions (P ϭ 0.013). Conclusion:Our results suggest that the spinal cord may still be affected by MS, even when lesions are not detected on a conventional MR scan. In addition, we demonstrated that diffusion tensor tractography is a robust tool to analyze the spinal cord of MS patients.

Using functional MRI, we investigate the neural correlates of intrinsic versus extrinsic motivation to cooperate by comparing people who differ in the personality trait Social Value Orientation. Participants (n ϭ 28) played several one-shot prisoner's dilemma games (offering weak cooperative incentives) and coordination games (offering strong cooperative incentives) with anonymous partners while they were under the scanner. Behavioral results indicate that proself individuals adjust their behavior toward more cooperation when extrinsic incentives were present, while prosocials' decisions are not affected by game context. The neurological data is consistent with a priori developed hypotheses regarding different behavioral strategies, and suggest that extrinsically motivated proself strategies are driven by calculation and a situation-by-situation approach. Increased activation was found in dorsolateral prefrontal cortex, posterior superior temporal sulcus (STS), and precuneus. Intrinsically motivated prosocials' strategies reflect norm compliance, routine moral judgment, and social awareness. Increased activation was found in lateral orbitofrontal cortex, anterior STS, and inferior parietal lobule.

When people are confronted with social dilemmas, their decision-making strategies tend to be associated with individual social preferences; prosocials have an intrinsic willingness to cooperate, while proselfs need extrinsic motivators signaling personal gain. In this study, the biological roots for the proselfs/prosocials concept are explored by investigating the neural correlates of cooperative versus defect decisions when participants engage in a series of one-shot, anonymous prisoner's dilemma situations. Our data are in line with previous studies showing that prosocials activate several social cognition regions of the brain more than proselfs (here: medial prefrontal cortex, temporo-parietal junction, and precuneus BA 7 (Brodmann area 7), and that dispositional trust positively affects prosocials' decisions to cooperate. At the neural level, however, dispositional trust appears to exert a greater marginal effect on brain activity of proselfs in three social cognition regions, which does not translate into an increase in cooperation. An event-related analysis shows that cooperating prosocials show significantly more activation in the precuneus (BA 7) than proselfs. Based on previous research, we interpret this result to be consistent with prosocials' enhanced tendency to infer the intentions of others in social dilemma games, and the importance of establishing norm congruence when they decide to cooperate.

This study uses fMRI to investigate the cognitive demands of decision-making in two types of cooperation games: a prisoner's dilemma (PD) eliciting a temptation to free-ride, leading to a dominant, self-interested response, and a stag hunt (SH) that has no dominant response but offers pay-off incentives that make mutual cooperation collectively beneficial but risky. Consequently, the PD poses greater conflict between self- and collective interest, greater demands for computational reasoning to derive the optimal solution, and greater demands for mentalizing to infer the intentions of others. Consistent with these differences between the two games, the results indicate that the PD is associated with increased activity in the anterior cingulate gyrus, prefrontal cortex, parietal lobe, and temporoparietal junction. With less conflict, the demands for computation and mentalizing are reduced in the SH, and cooperation levels increase dramatically. The differences in brain activation elicited by the different incentive structures of the PD and the SH appear to be independent of individual differences in revealed social preferences.