title: Corticospinal tract anatomy and functional connectivity of primary motor cortex in autism.
abstract: OBJECTIVE
  Growing evidence indicates that autism spectrum disorder (ASD) stems from abnormal structural and functional connectivity of neural networks. Although diagnostic symptoms are sociocommunicative, motor-related functions (beyond repetitive mannerisms) are also impaired. However, evidence on connectivity at the level of basic motor execution is limited, which we address here.
  
  
  METHODS
  We compared right-handed children and adolescents (aged 7-18 years) with ASD (n = 44) to matched typically developing participants (TD, n = 36) using magnetic resonance imaging (MRI). Diffusion-weighted imaging and probabilistic tractography measured microstructure of the corticospinal tract (CST). Intrinsic functional connectivity MRI examined whole-brain voxelwise correlations, both with identical precentral gyrus (PCG) seeds.
  
  
  RESULTS
  In the group with ASD, radial and mean diffusivity were increased bilaterally in the CST, particularly in superior segments, and a leftward asymmetry of CST volume detected in the TD group was reversed. Functionally, overconnectivity was found for both left and right PCG with prefrontal, parietal, medial occipital, and cingulate cortices. The group with ASD also showed significantly reduced asymmetry of functional connectivity for both left and right PCG seeds. Finally, in the group with ASD, significant correlations were found for functional overconnectivity of the right PCG seed with anisotropy and mean diffusivity in the right CST.
  
  
  CONCLUSIONS
  The findings, implicating both functional and anatomical connectivity of the primary motor cortex, suggest that network anomalies in ASD go well beyond sociocommunicative domains, affecting basic motor execution. They also suggest that even in right-handed adolescents with ASD, typical left hemisphere dominance is reduced, both anatomically and functionally, with an unusual degree of right hemisphere motor participation.
authors.affiliation: Brain Development Imaging Laboratory at San Diego State University, CA. Electronic address: rcarper@mail.sdsu.edu.
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Carper
authors.affiliation: Brain Development Imaging Laboratory at San Diego State University, CA.
authors.forename: Seraphina
authors.initials: S
authors.lastname: Solders
authors.affiliation: School of Medicine, University of California, San Diego.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Treiber
authors.affiliation: Brain Development Imaging Laboratory at San Diego State University, CA.
authors.forename: Inna
authors.initials: I
authors.lastname: Fishman
authors.affiliation: Brain Development Imaging Laboratory at San Diego State University, CA.
authors.forename: Ralph-Axel
authors.initials: RA
authors.lastname: Müller
mesh_terms: D000293:Adolescent; D016880:Anisotropy; D000067877:Autism Spectrum Disorder / Q000503:physiopathology*; D001931:Brain Mapping; D002140:California; D002648:Child; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000473:pathology*; D009415:Nerve Net / Q000503:physiopathology; D009434:Neural Pathways / Q000503:physiopathology; D011446:Prospective Studies; D011712:Pyramidal Tracts / Q000473:pathology*
keywords: autism spectrum disorder; diffusion tensor imaging; functional connectivity MRI; primary motor cortex; probabilistic tractography