Abstract
Substantial experimental evidence supports the theory that the dopaminergic system codes a phasic (short duration) signal predicting the delivery of primary reinforcers, such as water when thirsty, during Pavlovian learning. This signal is described by the temporal difference (TD) model. Recently, it has been suggested that the human dopaminergic system also codes more complex cognitive goal states, including those required for human social interaction. Using functional magnetic resonance imaging (fMRI) with 18 healthy subjects, we tested the hypothesis that TD signals would be present during a Pavlovian learning task, and during a social motor response learning task. Using an identical model, TD signals were present in both tasks, although in different brain regions. Specifically, signals were present in the dorsal anterior cingulate, ventral striatum, amygdala, and thalamus with Pavlovian learning, and the dorsal anterior cingulate and bilateral frontal operculum with social motor response learning. The frontal operculum is believed to be the human homologue of the monkey mirror neuron system, and there is evidence which links the region with inference about other peoples' intentions and goals. The results support the contention that the human dopaminergic system predicts both primary reinforcers, and more complex cognitive goal states, such as motor responses required for human social group interaction. Dysfunction of such a mechanism might be associated with abnormal affective responses and incorrect social predictions, as occur in psychiatric disorders.