title: Hemispheric asymmetry in myelin after stroke is related to motor impairment and function.
abstract: The relationships between impairment, function, arm use and underlying brain structure following stroke remain unclear. Although diffusion weighted imaging is useful in broadly assessing white matter structure, it has limited utility in identifying specific underlying neurobiological components, such as myelin. The purpose of the present study was to explore relationships between myelination and impairment, function and activity in individuals with chronic stroke. Assessments of paretic upper-extremity impairment and function were administered, and 72-hour accelerometer based activity monitoring was conducted on 19 individuals with chronic stroke. Participants completed a magnetic resonance imaging protocol that included a high resolution T1anatomical scan and a multi-component T2relaxation imaging scan to quantify myelin water fraction (MWF). MWF was automatically parcellated from pre- and post-central subcortical regions of interest and quantified as an asymmetry ratio (contralesional/ipsilesional). Cluster analysis was used to group more and less impaired individuals based on Fugl-Meyer upper extremity scores. A significantly higher precentral MWF asymmetry ratio was found in the more impaired group compared to the less impaired group (p< 0.001). There were no relationships between MWF asymmetry ratio and upper-limb use. Stepwise multiple linear regression identified precentral MWF asymmetry as the only variable to significantly predict impairment and motor function in the upper extremity (UE). These results suggest that asymmetric myelination in a motor specific brain area is a significant predictor of upper-extremity impairment and function in individuals with chronic stroke. As such, myelination may be utilized as a more specific marker of the neurobiological changes that predict long term impairment and recovery from stroke.
authors.affiliation: Department of Physical Therapy, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Bimal
authors.initials: B
authors.lastname: Lakhani
authors.affiliation: Department of Physical Therapy, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; Stroke Division, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, VIC 3084, Australia; NHMRC Centre of Research Excellence in Stroke Rehabilitation and Brain Recovery, Australia.
authors.forename: Kathryn S
authors.initials: KS
authors.lastname: Hayward
authors.affiliation: Department of Physical Therapy, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Lara A
authors.initials: LA
authors.lastname: Boyd
mesh_terms: D061725:Accelerometry; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D000068079:Motor Disorders / Q000000981:diagnostic imaging / Q000209:etiology*; D009186:Myelin Sheath / Q000378:metabolism / Q000473:pathology*; D020521:Stroke / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology; D034941:Upper Extremity / Q000503:physiopathology
keywords: AC, Activity Count; ANCOVA, Analysis of Covariance; AR, Asymmetry Ratio; Accelerometry; Biomarkers; CST, Corticospinal Tract; DTI, Diffusion Tensor Imaging; FM, Fugl-Meyer; GRASE, Gradient and Spin Echo; MANCOVA, Multivariate Analysis of Covariance; MR, Magnetic Resonance; MWF, Myelin Water Fraction; Motor control; Myelin; Stroke; UE, Upper Extremity; WMFT, Wolf Motor Function Test; White matter