What Parts of the Brain Are Involved in Repetitive Behavior?

We know less about the neural mechanisms behind repetitive behavior than the other two diagnostic features for ASD.

Several lines of evidence point to the cortico-basal ganglia loop as the brain regions most likely to be involved in repetitive behavior. Both a functional MRI study and a PET scan study of metabolic brain activity showed reduced connectivity between one of the areas within the basal ganglia, the caudate nucleus, and the motor cortex in ASD subjects, although the studies did not directly correlate the brain change to repetitive behavior. A recent study exploring whether overall patterns of brain activity from whole brain structural MRI scans could distinguish ASD patients from neurotypical controls confirmed differences in the cortical-basal ganglia loop, along with the cerebellum[1].

The size of the caudate nucleus has been shown to be bigger in school-aged children (ages 7-14) and adults with ASD compared to neurotypical patients[2]. However, studies of pre-school aged children found the regions to be smaller[3]. Other studies have found no difference after controlling for cerebral volume[4][5]! Differences between studies may be due to different ages of subjects, small sample sizes, or whether or not the sizes were relative to overall brain size or cerebral cortex size.

The basal ganglia has also been implicated in other neurodevelopmental disorders, including Obsessive Compulsive Disorder and Tourette’s syndrome, with an associated increase in excitability and abnormal cortical-basal ganglia circuitry. The size of the caudate is correlated with severity of symptoms for Tourette’s.

Some of the more complicated ritualized behaviors share similarities with habits, which are are motor patterns that proceed without conscious cognitive control. The cortico-basal ganglia loop has been implicated in the transition from goal-directed to habit-driven behavior, as seen with changes in neuronal activity.

An important neurotransmitter in the basal ganglia is dopamine. Recently, a specific receptor for dopamine, the DRD3 receptor, has been shown to be associated with one type of repetitive behavior, Insistence on Sameness[6]. Part of the gene for this receptor has been shown to be affected by the only medicines approved by the FDA for repetitive behavior: risperidone and aripripazole.