The measurements and mechanisms of restricted and repetitive behaviors in autism spectrum disorders

Abstract

Restricted and repetitive behaviors (RRBs) are one of the core features of autism spectrum disorders (ASD). RRBs encompass a broad range of heterogeneous behaviors, such as repetitive and stereotyped motor behavior or speech, atypical sensory behavior, inflexible interest and rituals, and insistence on the sameness of environment. While a large amount of previous research has focused on social deficits in ASD, little attention has been paid to their RRBs. The definition, classification, and underlying mechanism of RRBs have remained to be clarified. Recently, Diagnostic and Statistical Manual of Mental Disorders (5th ed, DSM-V) has classified RRBs into several subcategories and renewed the diagnostic criteria of RRBs. New theories and evidence from neurobiological, cognitive psychological, and developmental psychological research are also emerging about the etiology of RRBs. The first aim of this review is to introduce the newest definition and subcategories of RRBs based on DSM-V. We also discuss and compare different structural models of RRBs derived from several factor analysis studies. The second aim is to summarize the current assessment tools of RRBs in autism. Besides the “golden standard” -- the Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview-Revised (ADI-R), and several common used questionnaires such as Repetitive Behavior Scale-Revised (RBS-R) and Repetitive Behavior Questionnaire-2 (RBQ-2), new techniques including eye-tracking, accelerometry, and electrodermal activity (EDA) have been applied into the studies of RRBs. The third aim of this review is to discuss the potential causal origins underlying the RRBs. The neurobiological and cognitive mechanism of RRBs, as well as other factors that directly related to the onset of RRBs have been summarized. The neurobiological evidence indicates that the atypical activity of neurotransmitters, the imbalanced activity among the corticostriatal circuits, and the neuroanatomical alterations play important roles on the RRBs. From the perspective of cognitive psychology, classical theories such as executive functions, weak central coherence, extreme male brain theory, and operational conditioning all offer their own explanations for the onset of RRBs. Besides, the hyper- or hypo-arousal theory indicates that RRBs may function as coping strategies for the individuals with ASD to regulate levels of arousal or anxiety, with the intolerance of uncertainty as the mediator. The evidence from developmental psychology focus on the developmental trajectory of RRBs across age. Results from longitudinal studies identify the significant influence of age and intelligence on the developmental trajectory of RRBs. Severe impacts of environmental deprivation and social isolation on the RRBs have also been shown in animal and human studies and provide implication for early intervention. Finally, several future directions for the research on RRBs in ASD have also been proposed based on the current literature. We recommend future research that focuses on the united standard for classification and the direct connection between neurobiology and behavior. Also, a clear understanding of the developmental trajectories of RRBs in typical developing children and children with ASD is of importance for effective early interventions. Last but not least, the characteristics of parents and the prenatal maternal stress are worthy of future investigations.