Objectives: To assess fMRI, psychophysiological, behavioral, and subjective responses to standard laboratory reward stimuli as well as stimuli relevant to core autism symptoms.
Methods: We present a series of interconnected functional magnetic resonance (fMRI) and psychophysiological studies in groups of individuals with autism and matched controls. The fMRI studies used a monetary incentive delay (MID) task designed to assess responses during both anticipatory and outcome phases of reward processing. The psychophysiological studies examined affective modulation of the startle eyeblink and post-auricular reflexes. Across all studies, responses were assessed to (1) standard laboratory rewards; (2) images of non-social objects that have shown to garner greater visual attention in autism (e.g., trains, electronics, etc); and (3) images of faces.
Results: fMRI studies indicated that participants with autism showed decreased nucleus accumbens activation while anticipating and receiving monetary rewards. Responses to autism-relevant non-social objects revealed hyperactivation in ventromedial prefrontal cortex during reward outcomes in the autism group. Responses to social rewards revealed hyperactivation in bilateral amygdala during face anticipation and in bilateral insular cortex during face outcomes in the autism group, and responses to social rewards predicted the severity of autism symptoms.
Psychophysiology data revealed anomalous eyeblink and post-auricular reflex modulation and corrugator patterns to both IAPS images and images of faces, but not to salient non-social objects. These fMRI and psychophysiology results stand in stark contrast to self-report and behavioral responses to the same stimuli, suggesting dissociations between neurobiological, behavioral, and subjective responses to rewards.
Conclusions: Results suggest that autism is characterized by reward system dysfunction, but that the nature of this dysfunction is category-specific and dependent on the temporal phase of reward processing. We interpret these findings within the broader context of the functions of the reward system, namely to facilitate behavioral approach towards biologically meaningful goals. In this context, these data suggest that individuals with autism are characterized by decreased motivation towards primary rewards and social stimuli, but intact incentive responses towards certain categories of autism-specific, non-social rewards. The potential clinical implications of these results will be discussed.