Combined effect of motor imagery and peripheral nerve electrical stimulation on the motor cortex

Abstract

Although motor imagery enhances the excitability of the corticospinal tract, there are no peripheral afferent inputs during motor imagery. In contrast, peripheral nerve electrical stimulation (ES) can induce peripheral afferent inputs; thus, a combination of motor imagery and ES may enhance the excitability of the corticospinal tract compared with motor imagery alone. Moreover, the level of stimulation intensity may also be related to the modulation of the excitability of the corticospinal tract during motor imagery. Here, we evaluated whether a combination of motor imagery and peripheral nerve ES influences the excitability of the corticospinal tract and measured the effect of ES intensity on the excitability induced during motor imagery. The imagined task was a movement that involved touching the thumb to the little finger, whereas ES involved simultaneous stimulation of the ulnar and median nerves at the wrist. Two different ES intensities were used, one above the motor threshold and another above the sensory threshold. Further, we evaluated whether actual movement with afferent input induced by ES modulates the excitability of the corticospinal tract as well as motor imagery. We found that a combination of motor imagery and ES enhanced the excitability of the motor cortex in the thenar muscle compared with the other condition. Furthermore, we established that the modulation of the corticospinal tract was related to ES intensity. However, we found that the excitability of the corticospinal tract induced by actual movement was enhanced by peripheral nerve ES above the sensory threshold.

The modulatory effect of electrical stimulation on the excitability of the corticospinal tract varies according to the type of muscle contraction being performed

“…During the shortening contraction task, low-intensity electrical nerve stimulation increased the excitability of the corticospinal tract, but high-intensity electrical nerve stimulation did not. This is consistent with the results found in our previous study, in which the effect of electrical stimulation on corticospinal excitability was dependent on stimulus intensity ( Saito et al, 2013 ).…”

“…The stimulation intensity was effective in modulating the change in corticospinal excitability by electrical stimulation with voluntary movement. When the stimulated muscle is voluntarily shortened, low-intensity electrical stimulation displays significantly increased corticospinal excitability than high-intensity electrical stimulation ( Saito et al, 2013 ). However, the effect of stimulation intensity on corticospinal excitability is considered to depend on whether or not the stimulated muscle is active.…”

“…The synergistic effect of afferent input by electrical stimulation and somatosensory input by voluntary movement is known to play an important role in modulating corticospinal excitability ( Kido Thompson and Stein, 2004 ; Khaslavskaia and Sinkjaer, 2005 ; Barsi et al, 2008 ; Saito et al, 2013 ; Sugawara et al, 2013 ). However, it remains unknown whether the effect of stimulation intensity on corticospinal excitability is dependent on the type of muscle contraction being performed.…”

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.…”

Towards the integration of mental practice in rehabilitation programs. A critical review

“…The findings of such studies contribute to the refining of future experimental paradigms in RCTs (Dobkin, 2009). For patients with difficulty in engaging in MI, the enhancing effects of brain stimulation, such as Transcranial Direct Current Stimulation (Ang et al, 2012; Foerster et al, 2013) or peripheral stimulation (Saito et al, 2013), on MI may prove to be useful. We also need to examine more closely the brain changes associated with MI training and also to characterize the effects of different modes of MI delivery using neuroimaging methodology such as Near Infrared Spectroscopy (NIRS) that is more amenable to recording changes in brain function during functional activities (Mihara et al, 2013).…”