Reinforcement learning is a fundamental mechanism displayed by many species from mice to humans. However, adaptive behaviour depends not only on learning associations between actions and outcomes that affect ourselves, but critically, also outcomes that affect other people. Existing studies suggest reinforcement learning ability declines across the lifespan and self-relevant learning can be computationally separated from learning about rewards for others, yet how older adults learn what rewards others is unknown. Here, using computational modelling of a probabilistic reinforcement learning task, we tested whether young (age 18-36) and older (age 60-80, total n=152) adults can learn to gain rewards for themselves, another person (prosocial), or neither individual (control). Detailed model comparison showed that a computational model with separate learning rates best explained how people learn associations for different recipients. Young adults were faster to learn when their actions benefitted themselves, compared to when they helped others. Strikingly however, older adults showed reduced self-bias, with a relative increase in the rate at which they learnt about actions that helped others, compared to themselves. Moreover, we find evidence that these group differences are associated with changes in psychopathic traits over the lifespan. In older adults, psychopathic traits were significantly reduced and negatively correlated with prosocial learning rates. Importantly, older people with the lowest levels of psychopathy had the highest prosocial learning rates. These findings suggest learning how our actions help others is preserved across the lifespan with implications for our understanding of reinforcement learning mechanisms and theoretical accounts of healthy ageing

The decision to share resources is fundamental for cohesive societies. Humans can be motivated to give for many reasons. Some generosity incurs a definite cost, with no extrinsic reward to the act, but instead provides intrinsic satisfaction (labelled here as ‘altruistic’ giving). Other giving behaviours are done with the prospect of improving one’s own situation via reciprocity, reputation, or public good (labelled here as ‘strategic’ giving). These contexts differ in the source, certainty, and timing of rewards as well as the inferences made about others' mental states. We executed a combined statistical map and coordinate-based fMRI meta-analysis of decisions to give (36 studies, 1150 participants). Methods included a novel approach for accommodating variable signal dropout between studies in meta-analysis. Results reveal consistent, cross-paradigm neural correlates of each decision type, commonalities, and informative differences. Relative to being selfish, altruistic and strategic giving activate overlapping reward networks. However, strategic decisions showed greater activity in striatal regions than altruistic choices. Altruistic giving, more than strategic, activated subgenual anterior cingulate cortex (sgACC). Ventromedial prefrontal cortex (vmPFC) is consistently involved during generous decisions and processing across a posterior to anterior axis differentiates the altruistic/strategic context. Posterior vmPFC was preferentially recruited during altruistic decisions. Regions of the ‘social brain’ showed distinct patterns of activity between choice types, reflecting the different use of theory of mind in the two contexts. We provide the consistent neural correlates of decisions to give, and show that many will depend on the source of incentives.