Functional and structural asymmetry in primary motor cortex in Asperger syndrome: a navigated TMS and imaging study

Laura Säisänen,Timo A Lakka,Petro Julkunen,Heidi Gröhn,Eini Niskanen,Elisa Kallioniemi,Mervi Könönen,Samuli Kemppainen,Ritva Vanninen,Sara Määttä,Aino-Maija Eloranta,Ismo Makkonen,Niina Lintu

doi:10.1007/s10548-019-00704-0

Abstract

Motor functions are frequently impaired in Asperger syndrome (AS). In this study, we examined the motor cortex structure and function using navigated transcranial magnetic stimulation (nTMS) and voxel-based morphometry (VBM) and correlated the results with the box and block test (BBT) of manual dexterity and physical activity in eight boys with AS, aged 8–11 years, and their matched controls. With nTMS, we found less focused cortical representation areas of distinct hand muscles in AS. There was hemispheric asymmetry in the motor maps, silent period duration and active MEP latency in the AS group, but not in controls. Exploratory VBM analysis revealed less gray matter in the left postcentral gyrus, especially in the face area, and less white matter in the precentral area in AS as compared to controls. On the contrary, in the right leg area, subjects with AS displayed an increased density of gray matter. The structural findings of the left hemisphere correlated negatively with BBT score in controls, whereas the structure of the right hemisphere in the AS group correlated positively with motor function as assessed by BBT. These preliminary functional (neurophysiological and behavioral) findings are indicative of asymmetry, and co-existing structural alterations may reflect the motor impairments causing the deteriorations in manual dexterity and other motor functions commonly encountered in children with AS.

Highlights

Asperger syndrome (AS) is a neurodevelopmental condition belonging to the autism spectrum disorders (ASD)
No abnormalities related to motor areas were found in the magnetic resonance imaging (MRI)
We found functional reorganization of motor cortex in pediatric AS population having fine motor impairment with navigated transcranial magnetic stimulation (nTMS) with concomitant abnormalities in structural MRI

Summary

Introduction

Asperger syndrome (AS) is a neurodevelopmental condition belonging to the autism spectrum disorders (ASD). There is no delay in language development or any significant cognitive delay in AS Motor dysfunction such as motor clumsiness, awkwardness and motor learning delays are often present in children with ASD appearing early in life (Enticott et al 2013). Since motor dysfunctions are more quantifiable and better reproduced than the more complex communicative and social behaviors, their assessment may help in identifying and classifying children with the disorder (Behere et al 2012). These, according to neurodevelopmental model cannot be linked to specific cerebral lesions They are commonly observed in typically developing younger children, but their persistence into later childhood and adolescence is linked with an increased risk of psychiatric disorders (D’Agati et al 2018). It is essential to clarify the neural mechanisms underlying motor development and its dysfunction in ASD as they are the basis for the neurobiological background of the disorder

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