title: Task-dependent modulation of inputs to proximal upper limb following transcranial direct current stimulation of primary motor cortex.
abstract: Cathodal transcranial DC stimulation (c-tDCS) suppresses excitability of primary motor cortex (M1) controlling contralateral hand muscles. This study assessed whether c-tDCS would have similar effects on ipsi- and contralateral M1 projections to a proximal upper limb muscle. Transcranial magnetic stimulation (TMS) of left M1 was used to elicit motor evoked potentials (MEPs) in the left and right infraspinatus (INF) muscle immediately before and after c-tDCS of left M1, and at 20 and 40 min, post-c-tDCS. TMS was delivered as participants preactivated each INF in isolation (left, right) or both INF together (bilateral). After c-tDCS, ipsilateral MEPs in left INF and contralateral MEPs in right INF were suppressed in the left task but not in the bilateral or right tasks, indicative of task-dependent modulation. Ipsilateral silent period duration in the left INF was reduced after c-tDCS, indicative of altered transcallosal inhibition. These findings may have implications for the use of tDCS as an adjunct to therapy for the proximal upper limb after stroke.
authors.affiliation: Movement Neuroscience Laboratory, University of Auckland, Auckland, New Zealand.
authors.forename: Lynley V
authors.initials: LV
authors.lastname: Bradnam
authors.forename: Cathy M
authors.initials: CM
authors.lastname: Stinear
authors.forename: Gwyn N
authors.initials: GN
authors.lastname: Lewis
authors.forename: Winston D
authors.initials: WD
authors.lastname: Byblow
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology*; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009433:Neural Inhibition; D011712:Pyramidal Tracts / Q000502:physiology; D013647:Task Performance and Analysis; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult