title: Impact of 5-Hz rTMS over the primary sensory cortex is related to white matter volume in individuals with chronic stroke.
abstract: Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique that may facilitate mechanisms of motor learning. In a recent single-blind, pseudo-randomized study, we showed that 5-Hz rTMS over ipsilesional primary somatosensory cortex followed by practice of a skilled motor task enhanced motor learning compared with sham rTMS + practice in individuals with chronic stroke. However, the beneficial effect of stimulation was inconsistent. The current study examined how differences in sensorimotor cortex morphology might predict rTMS-related improvements in motor learning in these individuals. High-resolution T1-weighted magnetic resonance images were acquired and processed in FreeSurfer using a newly developed automated, whole brain parcellation technique. Gray matter and white matter volumes of the ipsilesional primary somatosensory and motor cortices were extracted. A significant positive association was observed between the volume of white matter in the primary somatosensory cortex and motor learning-related change, exclusively in the group that received active 5-Hz rTMS. A regression model with age, gray matter and white matter volumes as predictors was significant for predicting motor learning-related change in individuals who received active TMS. White matter volume predicted the greatest amount of variance (47.6%). The same model was non-significant when volumes of the primary motor cortex were considered. We conclude that white matter volume in the cortex underlying the TMS coil may be a novel predictor for behavioral response to 5-Hz rTMS over the ipsilesional primary somatosensory followed by motor practice.
authors.affiliation: Department of Physical Therapy, Faculty of Medicine, University of British Columbia, 212-2177 Wesbrook Mall, Vancouver, BC, Canada, V6T 1Z3.
authors.forename: Sonia M
authors.initials: SM
authors.lastname: Brodie
authors.forename: Michael R
authors.initials: MR
authors.lastname: Borich
authors.forename: Lara A
authors.initials: LA
authors.lastname: Boyd
mesh_terms: D000368:Aged; D002908:Chronic Disease; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000473:pathology / Q000503:physiopathology*; D013003:Somatosensory Cortex / Q000473:pathology / Q000503:physiopathology*; D020521:Stroke / Q000473:pathology / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation; D066127:White Matter / Q000473:pathology
keywords: FreeSurfer; motor learning; rTMS response; regional parcellation; volumetric segmentation