Studies suggest that dopaminergic neurons report a unitary, global reward prediction error signal. However, learning in complex real-life tasks, in particular tasks that show hierarchical structure, requires multiple prediction errors that may coincide in time. We used functional neuroimaging to measure prediction error signals in humans performing such a hierarchical task involving simultaneous, uncorrelated prediction errors. Analysis of signals in a priori anatomical regions of interest in the ventral striatum and the ventral tegmental area indeed evidenced two simultaneous, but separable, prediction error signals corresponding to the two levels of hierarchy in the task. This result suggests that suitably designed tasks may reveal a more intricate pattern of firing in dopaminergic neurons. Moreover, the need for downstream separation of these signals implies possible limitations on the number of different task levels that we can learn about simultaneously.

BackgroundPeople with autism have abnormal preferences, ranging from an apparent lack of preference for social stimuli to unusually strong preferences for restricted sets of highly idiosyncratic stimuli. Yet the profile of preferences across social and nonsocial domains has not been mapped out in detail, and the processes responsible remain poorly understood.MethodsTo assess preferences across a range of stimuli, we measured real monetary donations to 50 charities spanning categories pertaining to people, mental health, animals, or the environment. We compared the donations made by 16 high-functioning adults with autism to those made by neurotypical controls matched on age, gender and education. We additionally collected ratings of how people evaluated the different charities.ResultsCompared with controls, high-functioning adults with autism donated less overall and also showed a significantly disproportionate reduction in donations to people charities compared with donations to the other charities. Furthermore, whereas controls discriminated strongly between different people charities, choosing to donate a lot of money to some and very little to others, much less discrimination was seen in the autism group. Ratings that probed how participants constructed their preferences did not differ between groups, except for a difference in the perceived impact of pictures and text information about people charities. Strikingly, there were some charities related to mental health, and autism in particular, to which the autism group donated considerably more than did the controls.ConclusionsPeople with autism were found to have reduced preference and sensitivity towards charities benefiting other people. The findings provide evidence for a domain-specific impairment in social cognition in autism spectrum disorder, and in particular in linking otherwise intact social knowledge to the construction of value signals on which preferences regarding other people are based.