Enhanced motor noise in an autism subtype with poor motor skills

Early motor difficulties are a common in many, but not all, autistic individuals. These difficulties tend to be highly present in individuals carrying rare genetic mutations with high penetrance for autism. Many of these rare genetic mechanisms also cause neurophysiological dysregulation of excitation-inhibition balance (E:I). A predicted downstream consequence of E:I imbalance in motor circuitry would translate behaviorally into enhanced ‘motor noise’ – that is, increased variability in execution of motor actions. Here we tested the hypothesis that autistic individuals with the most pronounced motor difficulties would be most affected by enhanced motor noise. Unsupervised data-driven clustering on a standardized test of motor skills (n=156, age = 3-16 years) identified the presence of two robust and highly stable autism motor subtypes described by relatively intact versus highly impaired motor skills. With motor kinematics data recorded during a simple reach-to-drop task, we observed that enhanced motor noise is a specific characteristic of the autism subtype with highly impaired motor skills. Autistic individuals with poor motor skills may be differentially affected by E:I imbalance within motor circuitry.