This dissertation examined the reward system in children with autism spectrum disorders (ASD). I empirically tested the social motivation hypothesis as a potential explanation for social impairments in ASD. Chapter 1 investigated typically developing (TD) children's electrophysiological responses to rewards accompanied by incidental social versus nonsocial stimuli. This chapter introduced a paradigm that allows reward anticipation to be measured while controlling for both reward and stimulus properties. TD children had increased activation while anticipating rewards accompanied by social versus nonsocial stimuli, suggesting that TD children find social stimuli more rewarding than nonsocial stimuli. Chapter 2 investigated how children with ASD compare to TD children on reward anticipation and processing using the paradigm described in Chapter 1. TD children had larger reward anticipation for social versus nonsocial stimuli, while children with ASD did not. Children with ASD also processed social versus nonsocial stimuli differently than their TD peers. These results suggest that children with ASD have selective deficits in anticipation and processing of social rewards. Chapter 3 examined whether familiarity might normalize social reward anticipation for children with ASD. Neither children with nor without ASD had different magnitudes of reward anticipation for familiar versus unfamiliar faces, or scrambled versions of those pictures. However, when collapsing across familiarity, results from Chapter 2 were replicated--TD children had larger reward anticipation for social versus nonsocial stimuli, while children with ASD did not. Chapter 3 also found evidence for an Nc-like component that occurred prior to social stimuli. This component was larger for TD children versus those with ASD. To explore possible mechanisms for these differences in social reward processing, Chapter 4 proposes oxytocin as a potential neuropeptide involved in social motivation. Chapter 4 reviews research on oxytocin's effect on social behavior in individuals with and without ASD, as well as implications for treatment of joint attention deficits in ASD. This chapter makes suggestions for future research that combine pharmacological and behavioral interventions in order to optimize outcomes. Collectively, this dissertation provides evidence in favor of the social motivation hypothesis, and important information about the nature of the reward system in children with ASD

Background

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition, and multiple theories have emerged concerning core social deficits. While the social motivation hypothesis proposes that deficits in the social reward system cause individuals with ASD to engage less in social interaction, the overly intense world hypothesis (sensory over-responsivity) proposes that individuals with ASD find stimuli to be too intense and may have hypersensitivity to social interaction, leading them to avoid these interactions.

Methods

EEG was recorded during reward anticipation and reward processing. Reward anticipation was measured using alpha asymmetry, and post-feedback theta was utilized to measure reward processing. Additionally, we calculated post-feedback alpha suppression to measure attention and salience. Participants were 6- to 8-year-olds with (N = 20) and without (N = 23) ASD.

Results

Children with ASD showed more left-dominant alpha suppression when anticipating rewards accompanied by nonsocial stimuli compared to social stimuli. During reward processing, children with ASD had less theta activity than typically developing (TD) children. Alpha activity after feedback showed the opposite pattern: children with ASD had greater alpha suppression than TD children. Significant correlations were observed between behavioral measures of autism severity and EEG activity in both the reward anticipation and reward processing time periods.

Conclusions

The findings provide evidence that children with ASD have greater approach motivation prior to nonsocial (compared to social) stimuli. Results after feedback suggest that children with ASD evidence less robust activity thought to reflect evaluation and processing of rewards (e.g., theta) compared to TD children. However, children with ASD evidence greater alpha suppression after feedback compared to TD children. We hypothesize that post-feedback alpha suppression reflects general cognitive engagement-which suggests that children with ASD may experience feedback as overly intense. Taken together, these results suggest that aspects of both the social motivation hypothesis and the overly intense world hypothesis may be occurring simultaneously.

Previous neuroimaging and electrophysiological studies have suggested that human made sounds are processed differently from non-human made sounds. Multiple groups have suggested that voices might be processed as "special," much like faces. Although previous literature has explored neural correlates of voice perception under varying task demands, few studies have examined electrophysiological correlates of attention while directly comparing human made and non-human made sounds. In the present study, we used event-related potentials (ERPs) to compare attention to human versus non-human made sounds in an oddball paradigm. ERP components of interest were the P300, and fronto-temporal positivity to voices (FTVP), which has been reported in previous investigations of voice versus non-voice stimuli. We found that participants who heard human made sounds as "target" or infrequent stimuli had significantly larger FTPV amplitude, shorter FTPV latency, and larger P300 amplitude than those who heard non-human sounds as "target" stimuli. Our results are in concordance with previous findings that human-made and non-human made sounds are processed differently, and expand upon previous literature by demonstrating increased attention to human versus non-human made sounds, even when the non-human made sounds are ones that require immediate attention in daily life (e.g. a car horn). Heightened attention to human-made sounds is important theoretically and has potential for application in tests of social interest in populations with autism.