Effects of Leg Motor Imagery Combined With Electrical Stimulation on Plasticity of Corticospinal Excitability and Spinal Reciprocal Inhibition

Abstract

Motor imagery (MI) combined with electrical stimulation (ES) enhances upper-limb corticospinal excitability. However, its after-effects on both lower limb corticospinal excitability and spinal reciprocal inhibition remain unknown. We aimed to investigate the effects of MI combined with peripheral nerve ES (MI + ES) on the plasticity of lower limb corticospinal excitability and spinal reciprocal inhibition. Seventeen healthy individuals performed the following three tasks on different days, in a random order: (1) MI alone; (2) ES alone; and (3) MI + ES. The MI task consisted of repetitive right ankle dorsiflexion for 20 min. ES was percutaneously applied to the common peroneal nerve at a frequency of 100 Hz and intensity of 120% of the sensory threshold of the tibialis anterior (TA) muscle. We examined changes in motor-evoked potential (MEP) of the TA (task-related muscle) and soleus muscle (SOL; task-unrelated muscle). We also examined disynaptic reciprocal inhibition before, immediately after, and 10, 20, and 30 min after the task. MI + ES significantly increased TA MEPs immediately and 10 min after the task compared with baseline, but did not change the task-unrelated muscle (SOL) MEPs. MI + ES resulted in a significant increase in the magnitude of reciprocal inhibition immediately and 10 min after the task compared with baseline. MI and ES alone did not affect TA MEPs or reciprocal inhibition. MI combined with ES is effective in inducing plastic changes in lower limb corticospinal excitability and reciprocal Ia inhibition.

Why brain-controlled neuroprosthetics matter: mechanisms underlying electrical stimulation of muscles and nerves in rehabilitation

“…When motor imagery was provided by means of watching and imagining actions shown on a pre-recorded video of grasping, while not producing the movements, it was shown that concurrent electrical stimulation facilitated MEP corticospinal excitability and that either motor imagery and electrical stimulation alone did not elicit any effects [ 157 ]. Similar acute effects were shown using combined motor imagery and electrical stimulation of the lower-limbs [ 137 ]. Preliminary results with chronic stroke patients also suggest that applying electrical stimulation in combination with motor imagery over the course of 10 days may possibly improve upper-limb function after the intervention cessation [ 106 ].…”

Intensity and dose of neuromuscular electrical stimulation influence sensorimotor cortical excitability

“…Cortical excitability modulation over corticospinal or corticomuscular connectivity (i.e., over the sensorimotor loop) has been demonstrated using transcranial magnetic stimulation (Fujisawa et al, 2011). Recent experiments investigated the relevant role of peripheral sensory stimulation intensity in influencing corticomotor excitability (Takahashi et al, 2019). While intensities above-motor-threshold induced stronger corticomotor output measured by means of motor evoked potentials (MEP), the results for stimulation below motor threshold led to no agreement, probably due to the wide range of stimulation parameters used in the existing literature (Carson and Buick, 2019;Chipchase et al, 2011).…”

“…The power change was computed as the percentage of increase or decrease in power (i.e., ERS or ERD) with respect to the baseline ([-2.5, -1.5] s), as described in Equation 4.From the time-frequency maps, we calculated the mean change in power of channels C1, C3, CP1 and CP3 (i.e., area over the sensorimotor cortex representing right forearm, contralateral hemisphere to the stimulated limb), since we considered that averaged values over these electrodes could better quantify the overall changes in the sensorimotor areas. We calculated the sensorimotor averaged changes in power in alpha[7][8][9][10][11][12][13] Hz and beta[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Hz bands for non-stimulation ([-3, -1] s) and NMES ([0.5, 2.5] s) intervals, using as baseline the [-2.5, -1.5] s interval (seeFigure 3). The NMES period was defined as starting at 0.5 s to avoid potential bias and influence of the stimulation onset like event-related brain potentials (e.g., error potentials, P300, etc.)…”

“…Then, the remaining clean data is filtered and divided into trials. Finally, power is estimated in alpha[7][8][9][10][11][12][13] Hz and beta[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Hz bands for non-stimulation ([-3, -1] s) and NMES([0.5, 2.5] s) intervals, being the baseline[-2.5, -1.5] s.…”

State-Dependent Gain Modulation of Spinal Motor Output

“…One potential mechanism is the increase of corticospinal gain modulation ( Khademi et al, 2018 , 2019 ; Naros et al, 2019 ). The focus of previous studies has been on the induced changes at the cortical level ( Gharabaghi, 2016 ), although there is some research on spinal changes following intervention at the lower limb ( Takahashi et al, 2019 ).…”