Direct and crossed effects of somatosensory electrical stimulation on motor learning and neuronal plasticity in humans.
OBJECTIVE
Sensory input can modify voluntary motor function. We examined whether somatosensory electrical stimulation (SES) added to motor practice (MP) could augment motor learning, interlimb transfer, and whether physiological changes in neuronal excitability underlie these changes.


METHODS
Participants (18-30 years, n = 31) received MP, SES, MP + SES, or a control intervention. Visuomotor practice included 300 trials for 25 min with the right-dominant wrist and SES consisted of weak electrical stimulation of the radial and median nerves above the elbow. Single- and double-pulse transcranial magnetic stimulation (TMS) metrics were measured in the intervention and non-intervention extensor carpi radialis.


RESULTS
There was 27 % motor learning and 9 % (both p < 0.001) interlimb transfer in all groups but SES added to MP did not augment learning and transfer. Corticospinal excitability increased after MP and SES when measured at rest but it increased after MP and decreased after SES when measured during contraction. No changes occurred in intracortical inhibition and facilitation. MP did not affect the TMS metrics in the transfer hand. In contrast, corticospinal excitability strongly increased after SES with MP + SES showing sharply opposite of these effects.


CONCLUSIONS
Motor practice and SES each can produce motor learning and interlimb transfer and are likely to be mediated by different mechanisms. The results provide insight into the physiological mechanisms underlying the effects of MP and SES on motor learning and cortical plasticity and show that these mechanisms are likely to be different for the trained and stimulated motor cortex and the non-trained and non-stimulated motor cortex.
Center for Human Movement Sciences, University of Groningen, University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV FA23, Groningen, The Netherlands. m.p.veldman@umcg.nl.
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MP
Veldman
Department of Neuroscience, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
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Zijdewind
Motor Control Laboratory, Department of Kinesiology, Pennsylvania State University, State College, PA, USA.|University School of Physical Education, Wroclaw, Poland.
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Solnik
Neuromuscular Research Laboratory, Schulthess Clinic, Zurich, CH, Switzerland.
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Maffiuletti
Center for Human Movement Sciences, University of Groningen, University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV FA23, Groningen, The Netherlands.
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Berghuis
Department of Health Sciences and Technology, ETH Zurich, Zurich, Switzerland.
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Javet
Department of Biomechanics, Kinesiology, and Informatics, University of Physical Education, Budapest, Hungary.
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Négyesi
Center for Human Movement Sciences, University of Groningen, University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV FA23, Groningen, The Netherlands.|Faculty of Health and Life Sciences, Northumbria University, Newcastle-upon-Tyne, UK.
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Hortobágyi
D000293:Adolescent; D000328:Adult; D019054:Evoked Potentials, Motor; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D007858:Learning; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D009048:Motor Skills; D009473:Neuronal Plasticity; D011712:Pyramidal Tracts / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D004561:Transcutaneous Electric Nerve Stimulation; D014953:Wrist / Q000502:physiology
Corticospinal excitability; Interlimb transfer; Motor evoked potential; Primary motor cortex; Transcranial magnetic stimulation