Abstract: Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by a persistent deficit in communication and social interaction, and restricted patterns of behavior, interests, or activities. The etiology of ASD has not yet been fully elucidated. Social deficits are at the core of ASD symptoms. Previous studies proposed that a deficit in theory of mind caused social impairment from a social cognitive perspective, but individuals with ASD already exhibited social motivation deficits traits prior to acquiring theory of mind. Moreover, some individuals who were able to pass theory-of-mind tests continued to show decreased motivation when engaging in social interactions. Social motivation theory suggests that social motivation is an important internal force for human evolution, motivating and sustaining individual social activities. It is also considered as a prerequisite for the development of social cognitive abilities. The theory of mind impairments and social deficits in individuals with ASD explains that these are due to deficits in social motivation. This theory can help to reverse the understanding of social impairments mechanism, achieving a shift from a social cognitive perspective to a socially motivated perspective. It can also have a positive impact on the clinical diagnosis and rehabilitation of ASD. For example, impaired neural mechanisms of social motivation can be used as an early warning biological indicator for diagnosis, for this reason, educators need to pay more attention to the impact of social motivation on the rehabilitation of ASD.
Social motivation theory provides a new interpretation of social deficits in ASD in terms of behavioral performance, neuroscience, and biology. Social stimuli elicit activity in the midbrain dopaminergic limbic reward system (considered to be the amygdala-striatal-orbital frontal cortex), which is seen as the neurobiological mechanism of social motivation. However, previous studies have shown that individuals with ASD process social rewards differently than typically developing individuals. For example, low levels of neurotransmitters are projected onto the midbrain dopaminergic limbic reward system in individuals with ASD during the processing of social stimuli. Meanwhile, individuals with ASD demonstrated attenuated ERP amplitudes and insufficient activation of the midbrain dopaminergic limbic reward system, especially the ventral striatum, in response to social stimuli. In addition, the major areas of the brain related to the processing of social sounds were inadequately connected to the reward system. This makes it difficult to obtain reward value from processing social stimuli and participating in social interaction. This further leads to a lack of motivation to actively explore social stimuli for individuals with ASD, specifically at the behavioral level, characterized by impaired social orientation, low levels of social seeking and liking, and deficits in social maintenance. Considered as a whole, these results suggest that individuals with ASD have processing deficits for social stimuli and lack motivation for social interaction. Meanwhile, insufficient social motivation deprives social information input and social learning opportunities during growth, especially during the critical period of social cognitive development, for individuals with ASD. This results in a lack of experience with social stimuli, and a traumatic development of normalized and specialized neural networks responsible for processing social information, ultimately leading to the emergence of social deficits in individuals with ASD.
In the future, it is important to further refine research on the role of two types of neural systems, namely the amygdala-striatum-orbital frontal cortex and midbrain dopaminergic limbic reward systems, in social motivation and the relationship between them. Further in this study, the scope of the application of social motivation theory in autism spectrum disorder groups is clarified. For instance, whether anxiety affects the level of social motivation in individuals with ASD? Moreover, the application of social motivation theory to assessment diagnosis and clinical rehabilitation is employed.

Key words: social motivation theory, autism spectrum disorder, social deficits, reward system