title: Change of facilitation during voluntary bilateral hand activation after stroke.
abstract: OBJECTIVE
  The relearning of daily activities after stroke also involves performance of bimanual tasks. This raises the possibility that concurrent activation of the healthy hemisphere interferes with reorganization processes in the affected hemisphere due to inhibitory pathways between homologous motor cortex representations. This study investigated the effect of voluntary, simultaneous activation of both hands upon the non-dominant (healthy subjects) or affected (stroke patients) hemisphere.
  
  
  METHODS
  Eleven healthy subjects and 16 stroke patients were investigated using transcranial stimulation (TMS). TMS was applied over the non-dominant/affected hemisphere during performance of an isometric pinch grip at different force levels (10% or 50% of maximal voluntary contraction) with the contralateral hand. The ipsilateral hand had to perform the pinch grip at various force levels (10%, 50%, or 100% of maximal voluntary contraction) simultaneously. Peak-to-peak amplitudes of motor evoked potentials (MEPs) were compared to assess differences in motor cortex excitability.
  
  
  RESULTS
  Unilateral activity of either hand alone exerted a facilitatory effect upon the non-dominant or affected hemisphere. In healthy subjects, the activation of the ipsilateral hand simultaneously with the contralateral hand did not produce any significant change of the MEP amplitudes compared to unilateral activation of the contralateral hand. In patients, however, the additional activation of the ipsilateral hand caused an additional increase of the peak-to-peak amplitudes.
  
  
  CONCLUSIONS
  In healthy subjects voluntary activation of the ipsilateral hand does not change the excitability of the motor cortex of the non-dominant hemisphere, when the contralateral hand is simultaneously activated. The facilitation of the contralateral hand seems to gate further facilitation by the ipsilateral hand. However, in stroke patients simultaneous activation of both hands causes an additional facilitation compared to activation of the affected hand alone.
authors.affiliation: NRZ, Neurological Rehabilitation Center, University of Leipzig, Muldentalweg 1 D-04828 Bennewitz bei Leipzig, Germany. renner@sachsenklinik.de
authors.forename: Caroline I E
authors.initials: CI
authors.lastname: Renner
authors.forename: Hartwig
authors.initials: H
authors.lastname: Woldag
authors.forename: Ruska
authors.initials: R
authors.lastname: Atanasova
authors.forename: Horst
authors.initials: H
authors.lastname: Hummelsheim
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000502:physiology / Q000503:physiopathology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000294:innervation / Q000503:physiopathology*; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009069:Movement Disorders / Q000209:etiology* / Q000503:physiopathology / Q000534:rehabilitation; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009434:Neural Pathways / Q000502:physiology / Q000503:physiopathology; D009473:Neuronal Plasticity / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D026741:Physical Therapy Modalities / Q000639:trends; D020127:Recovery of Function / Q000502:physiology*; D020521:Stroke / Q000150:complications*; D000071939:Stroke Rehabilitation; D050781:Transcranial Magnetic Stimulation