Motor imagery and electrical stimulation reproduce corticospinal excitability at levels similar to voluntary muscle contraction

Abstract

BackgroundThe combination of voluntary effort and functional electrical stimulation (ES) appears to have a greater potential to induce plasticity in the motor cortex than either electrical stimulation or voluntary training alone. However, it is not clear whether the motor commands from the central nervous system, the afferent input from peripheral organs, or both, are indispensable to induce the facilitative effects on cortical excitability. To clarify whether voluntary motor commands enhance corticospinal tract (CoST) excitability during neuromuscular ES, without producing voluntary muscular contraction (VMC), we examined the effect of a combination of motor imagery (MI) and electrical muscular stimulation on CoST excitability using transcranial magnetic stimulation (TMS).MethodsEight neurologically healthy male subjects participated in this study. Five conditions (resting, MI, ES, ES + MI [ESMI], and VMC) were established. In the ES condition, a 50-Hz stimulus was applied for 3 to 5 s to the first dorsal interosseous (FDI) while subjects were relaxed. In the MI condition, subjects were instructed to imagine abducting their index finger. In the ESMI condition, ES was applied approximately 1 s after the subject had begun to imagine index finger abduction. In the VMC condition, subjects modulated the force of index finger abduction to match a target level, which was set at the level produced during the ES condition. TMS was applied on the hotspot for FDI, and the amplitude and latency of motor evoked potentials (MEPs) were measured under each condition.ResultsMEP amplitudes during VMC and ESMI were significantly larger than those during other conditions; there was no significant difference in MEP amplitude between these 2 conditions. The latency of MEPs evoked during MI and VMC were significantly shorter than were those evoked during rest and ES.ConclusionsMEP acutely reinforced in ESMI may indicate that voluntary motor drive markedly contributes to enhance CoST excitability, without actual muscular contraction.

Effect of tactile stimulation on primary motor cortex excitability during action observation combined with motor imagery

“…(3) In the "OBS + ES" conditions, a reduction in the FDI MEP amplitude was observed without the motor imagery, whereas it showed an increased amplitude with the motor imagery. In the previous studies, it was reported that the somatosensory inputs combined with the motor imagery enhanced the M1 excitability [19,20]. Therefore, the experimental condition in which the ES effect combined during the motor imagery for the pinching action without action observation should be examined.…”

Entraining alpha activity using visual stimulation in patients with chronic musculoskeletal pain. A feasibility study

“…Another important source of variability in the effects of neurostimulation is brain-state dependency, i.e., the effect of neurostimulation depends on the timing of stimulation with respect to the underlying brain state. A number of studies have shown that applying neurostimulation in a brain-state dependent manner can enhance the modulation of corticospinal excitability (Kraus et al 2016;Kaneko et al 2014;Saito et al 2013). Ultimately, taking into account these factors in the application of neurostimulation should lead to a more personalized and adaptive neuromodulatory therapy to reduce chronic pain.…”

Provision of somatosensory inputs during motor imagery enhances learning-induced plasticity in human motor cortex

“…Because of this difference, practice is probably less accurate in MI, leading to a smaller improvement in motor performance 18 , 21 , 22 . Recent evidence in the literature showed that the combination of MI and peripheral nerve electrical stimulation above motor threshold was able to influence M1 excitability similarly to voluntary movement 19 , 20 . However no behavioural data are available in the literature so far on the efficacy of combined MI and peripheral stimulation training.…”

“…It has been recently demonstrated that the association of motor imagery and peripheral nerve electrical stimulation could enhance cortico-spinal excitability during MI practice, to a larger extent with respect to peripheral nerve electrical stimulation or MI alone 19 , 20 . Particularly, the combination of the activation of the internal model of motor commands, due to the MI, and the external activation of afferent input, given by peripheral nerve electrical stimulation led to a similar increase of the cortico-spinal excitability as real movement.…”