title: Timing of motor cortical stimulation during planar robotic training differentially impacts neuroplasticity in older adults.
abstract: OBJECTIVE
  The objective was to determine how stimulation timing applied during reaching influenced neuroplasticity related to practice. Older adult participants were studied to increase relevance for stroke rehabilitation and aging.
  
  
  METHODS
  Sixteen participants completed 3 sessions of a reaching intervention with 480 planar robotic movement trials. Sub-threshold, single-pulse transcranial magnetic stimulations (TMS) were delivered during the late reaction time (LRT) period, when muscle activity exceeded a threshold (EMG-triggered), or randomly. Assessments included motor evoked potentials (MEP), amplitude, and direction of supra-threshold TMS-evoked movements and were calculated as change scores from baseline.
  
  
  RESULTS
  The direction of TMS-evoked movements significantly changed after reaching practice (p<0.05), but was not significantly different between conditions. Movement amplitude changes were significantly different between conditions (p<0.05), with significant increases following the LRT and random conditions. MEP for elbow extensors and flexors, and the shoulder muscle that opposed the practice movement were significantly different between conditions with positive changes following LRT, negative changes following EMG-triggered, and no changes following the random condition. Motor performance including movement time and peak velocity significantly improved following the training but did not differ between conditions.
  
  
  CONCLUSIONS
  The responsiveness of the motor cortex to stimulation was affected positively by stimulation during the late motor response period and negatively during the early movement period, when stimulation was combined with robotic reach practice.
  
  
  CONCLUSIONS
  The sensitivity of the activated motor cortex to additional stimulation is highly dynamic.
authors.affiliation: Physical Therapy and Rehabilitation Sciences Department, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Crystal L
authors.initials: CL
authors.lastname: Massie
authors.affiliation: Moss Rehabilitation Research Institute, Elkins Park, PA 19027, USA; Physical Therapy and Rehabilitation Sciences Department, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Shailesh S
authors.initials: SS
authors.lastname: Kantak
authors.affiliation: Department of Neurology, University of Maryland School of Medicine, and Maryland Exercise and Robotics Center of Excellence, Veterans Affairs Medical Center, Baltimore, MD 21201, USA.
authors.forename: Priya
authors.initials: P
authors.lastname: Narayanan
authors.affiliation: Geriatrics Research, Education & Clinical Center, Veterans Affairs Medical Center, Baltimore, MD 21201, USA; Department of Neurology, University of Maryland School of Medicine, and Maryland Exercise and Robotics Center of Excellence, Veterans Affairs Medical Center, Baltimore, MD 21201, USA; Physical Therapy and Rehabilitation Sciences Department, University of Maryland School of Medicine, Baltimore, MD 21201, USA. Electronic address: gwittenb@grecc.umaryland.edu.
authors.forename: George F
authors.initials: GF
authors.lastname: Wittenberg
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009048:Motor Skills; D009068:Movement; D018482:Muscle, Skeletal / Q000502:physiology; D009473:Neuronal Plasticity; D011930:Reaction Time / Q000502:physiology; D012371:Robotics; D050781:Transcranial Magnetic Stimulation
keywords: Aging; Motor control; Neuroplasticity; Reaching; Rehabilitation; Transcranial magnetic stimulation