What Research Challenges Do We Face in Understanding Repetitive Behavior?

Identifying the cause of repetitive behavior in individuals with ASD and the best treatment is a challenge for five reasons:

1.  Children with ASD differ quantitatively, not qualitatively, in repetitive behaviors relative to neurotypical children. Repetitive behavior is a normal aspect of a child’s development. Why and how does it increase in frequency and duration in children with ASD? What are the neurobiological mechanisms that cause it to change from developmentally appropriate to developmentally inappropriate? We don’t know!

2. Excessive repetitive behavior is not unique to ASD, occurring in other neurodevelopmental disorders as well. This makes it hard to find a specific cause or treatment for patients with ASD.

3. Repetitive behavior takes different forms, each of which may have different causes.  Repetitive behaviors can be divided into four subtypes. None of the subtypes, however, are unique or specific to ASD[1]. It is likely that there are multiple causes of repetitive behavior, including anxiety, sensory-seeking, and communication difficulties which may cause frustration and lead to repetitive behavior[2].  Excessive repetitive behaviors themselves may also cause social problems by stigmatizing the child, leading to more repetitive behavior. Genetic studies suggest that pathological repetitive behavior is mediated by a very large number of genes.

4. None of the animal models of repetitive behavior are specific to autism. Excessive repetitive behavior such as pacing rarely occurs in wild mammals, including adult primates[3].  When it does happen, it is thought to be a pathological response to environmental or social deprivation. Observations of zoo animals and other caged animals show that restricted movement and environmental deprivation can lead to repetitive behavior. Social deprivation can also cause repetitive behaviors, as shown with animal studies and studies of children raised in severe social isolation in orphanages. Does such deprivation shed light on repetitive behaviors in children with ASD? We don’t know.  Other animal models are created with a targeted insult to the brain or are induced with drugs. Further, there are no animal models for some of the more complex repetitive behaviors, such as Insistence on Sameness.

5. Our knowledge of neural mechanisms of repetitive behavior is limited. No strong correlation is known linking repetitive behavior with specific cognitive, sensory, or motor abnormalities[4]. To date, no postmortem studies have been conducted linking brain changes with repetitive behavior[5]. Only a few MRI studies have looked at brain differences and repetitive behavior, and some results are contradictory. For example, some studies show an increased volume in the basal ganglia of children with ASD, while others do not[6]. The differences may be due to differences in the age of the subjects, a small sample size, differences in the subtype of repetitive behavior studied, or not controlling for overall cerebral cortex or brain volume[7].

[1] Lewis M, Kim S-J (2009) “The pathophysiology of restricted repetitive behavior.” J Neurodevelop Disord 1:114-132.

[2]  Ibid.

[3]  Thelen 1979.

[4] Lewis M, Kim S-J (2009) “The pathophysiology of restricted repetitive behavior.” J Neurodevelop Disord 1:114-132.

[5] Ibid.

[6]  Ibid.

[7] Estes A, Shaw DWW, Sparks BF, Friedman S, Giedd JN, Dawson G, Bryan M, Dager SR (2011) “Basal ganglia morphometry and repetitive behavior in young children with Autism Spectrum Disorder.” Autism Res 4: 212-220.