Changes in the Development of Striatum Are Involved in Repetitive Behavior in Autism.
Repetitive behavior is a core feature of autism and has been linked to differences in striatum. In addition, the brain changes associated with autism appear to vary with age.
However, most studies investigating striatal differences in autism are cross-sectional, limiting inferences on development. In this study, we set out to 1) investigate striatal development in autism, using a longitudinal design; and 2) examine the relationship between striatal development and repetitive behavior.
We acquired longitudinal structural magnetic resonance imaging scans from 86 individuals (49 children with autism, 37 matched control subjects). Each individual was scanned twice, with a mean scan interval time of 2.4 years. Mean age was 9.9 years at time 1 and 12.3 years at time 2. Striatal structures were traced manually with high reliability. Multivariate analyses of variance were used to investigate differences in brain development between diagnostic groups. To examine the relationship with behavior, correlations between changes in brain volumes and clinical measures were calculated.
Our results showed an increase in the growth rate of striatal structures for individuals with autism compared with control subjects.
The effect was specific to caudate nucleus, where growth rate was doubled.
Second, faster striatal growth was correlated with more severe repetitive behavior (insistence on sameness) at the preschool age.
This longitudinal study of brain development in autism confirms the involvement of striatum in repetitive behavior. Furthermore, it underscores the significance of brain development in autism, as the severity of repetitive behavior was related to striatal growth, rather than volume per se.
Further Readings of Interest
The striatum, also known as the neostriatum or striate nucleus, is a subcortical (i.e., inside, rather than on the outside) part of the forebrain. It is the major input station of the basal ganglia system. The striatum, in turn, gets input from the cerebral cortex. In primates (including humans), the striatum is divided by a white matter tract called the internal capsule into two sectors called the caudate nucleus and putamen. The term corpus striatum occasionally refers to the striatum combined with the globus pallidus, a structure closely related to the putamen, and the lenticular nucleus refers to the putamen together with the globus pallidus.
Functionally, the striatum helps coordinate body movement with motivation. The striatum helps balance and facilitate both higher-level motivations, such as inhibiting one’s behavior in a complex social interaction, and lower-level, fine-motor functions, such as inhibiting a small voluntary movement.
* The caudate nucleus is highly innervated by dopamine neurons. These neurons originate mainly from the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc). There are also additional inputs from various association cortices.
Learning and memory
Historically, the basal ganglia as a whole have been implicated in higher-order motor control. The caudate nucleus was initially thought to primarily be involved with control of voluntary movement. More recently, it has been demonstrated that the caudate is highly involved in learning and memory, particularly regarding feedback processing. In general, it has been demonstrated that neural activity will be present within the caudate while an individual is receiving feedback. People with hyperthymesia appear to have slight increases in the sizes of the caudate nucleus as well as of the temporal lobe of the cortex.
The brain contains large collections of neurons reciprocally connected by excitatory synapses, thus forming large network of elements with positive feedback. It is difficult to see how such a system can operate without some mechanism to prevent explosive activation. There is some indirect evidence that the caudate may perform this regulatory role by measuring the general activity of cerebral cortex and controlling the threshold potential.
Role in obsessive compulsive disorder
It has been theorized that the caudate nucleus may be dysfunctional in persons with obsessive compulsive disorder (OCD), in that it may perhaps be unable to properly regulate the transmission of information regarding worrying events or ideas between the thalamus and the orbitofrontal cortex.
A neuroimaging study with positron emission tomography found that the right caudate nucleus had the largest change in glucose metabolism after patients had been treated with paroxetine. Recent SDM meta-analyses of voxel-based morphometry studies comparing people with OCD and healthy controls have found people with OCD to have increased grey matter volumes in bilateral lenticular nuclei, extending to the caudate nuclei, while decreased grey matter volumes in bilateral dorsal medial frontal/anterior cingulate gyri. These findings contrast with those in people with other anxiety disorders, who evince decreased (rather than increased) grey matter volumes in bilateral lenticular / caudate nuclei, while also decreased grey matter volumes in bilateral dorsal medial frontal/anterior cingulate gyri.