Direct and crossed effects of somatosensory electrical stimulation on motor learning and neuronal plasticity in humans.

M P Veldman,I Zijdewind,K M M Berghuis,S Solnik,T Hortobágyi,N A Maffiuletti,M Javet,J Négyesi

doi:10.1007/s00421-015-3248-z

Abstract

PurposeSensory 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.MethodsParticipants (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.ResultsThere 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.ConclusionMotor 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.

Highlights

Sensory inputs from the environment provide feedback for the motor system to accurately perform motor tasks and are essential for motor learning (Gentilucci et al 1997; Rosenkranz and Rothwell 2012)
Corticospinal excitability increased after motor practice (MP) and somatosensory electrical stimulation (SES) when measured at rest but it increased after MP and decreased after SES when measured during contraction
We found that all three interventions produced motor learning and interlimb transfer but SES added to MP did not further increase learning and transfer (Table 2)

Summary

Introduction

Sensory inputs from the environment provide feedback for the motor system to accurately perform motor tasks and are essential for motor learning (Gentilucci et al 1997; Rosenkranz and Rothwell 2012). Reduced sensory function results in decreased manual motor function (Rothwell et al 1982) and interferes with the recovery of voluntary movements after a stroke (Nudo et al 2000). These observations led to the idea that enriched compared with normal sensory inputs could augment motor performance. The excitability of the corticospinal path as evaluated by the amplitude of motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) increased after bouts of SES in the stimulated (Charlton et al 2003; Kaelin-Lang et al 2002; Mang et al 2011; McKay et al 2002; Ridding et al 2000, 2001) and homologous contralateral muscles (Shin and Sohn 2011), confirming that unilateral SES can have non-focal, bilateral effects

Objectives

Methods

Results

Conclusion