Using Cutaneous Receptor Vibration to Uncover the Effect of Transcranial Magnetic Stimulation (TMS) on Motor Cortical Excitability

Abstract

Background Little is known about how vibrational stimuli applied to hand digits affect motor cortical excitability. The present transcranial magnetic stimulation (TMS) study investigated motor evoked potentials (MEPs) in the upper extremity muscle following high-frequency vibratory digit stimulation. Material/Methods High-frequency vibration was applied to the upper extremity digit II utilizing a miniature electromagnetic solenoid-type stimulator-tactor in 11 healthy study participants. The conditioning stimulation (C) preceded the test magnetic stimulation (T) by inter-stimulus intervals (ISIs) of 5–500 ms in 2 experimental sessions. The TMS was applied over the primary motor cortex for the hand abductor pollicis-brevis (APB) muscle. Results Dunnett’s multiple comparisons test indicated significant suppression of MEP amplitudes at ISIs of 200 ms ( P =0.001), 300 ms ( P =0.023), and 400 ms ( P =0.029) compared to control. Conclusions MEP amplitude suppression was observed in the APB muscle at ISIs of 200–400 ms, applying afferent signaling that originates in skin receptors following the vibratory stimuli. The study provides novel insight on the time course and MEP modulation following cutaneous receptor vibration of the hand digit. The results of the study may have implications in neurology in the neurorehabilitation of patients with increased amplitude of MEPs.

Location‐specific cutaneous electrical stimulation of the footsole modulates corticospinal excitability to the plantarflexors and dorsiflexors during standing

“…If true, it should be expected that the stimulation of cutaneous afferents is capable of altering corticospinal excitability, and in upper limb studies using TMS, this has been demonstrated (there is a scarcity of similar investigations in the lower limb). Across this upper limb research, many studies have shown that corticospinal excitability decreases following cutaneous afferent stimulation (Clouston et al, 1995 ; Inghilleri et al, 1995 ; Maertens de Noordhout et al, 1992 ; Manganotti et al, 1997 ; Rogić Vidaković et al, 2020 ; Tamburin et al, 2001 ), although some have shown no effect (Komori et al, 1992 ). Intuitively, it therefore could have been hypothesized in the present study that foot sole simulation would simply inhibit corticospinal excitability to the plantarflexors and dorsiflexors.…”

“…This could potentially be explained by changes in intracortical pathways, but literature on this topic does not seem to support it. In upper limb studies, although MEP amplitudes decrease following cutaneous stimulation (Clouston et al, 1995 ; Inghilleri et al, 1995 ; Maertens de Noordhout et al, 1992 ; Manganotti et al, 1997 ; Rogić Vidaković et al, 2020 ; Tamburin et al, 2001 ), cutaneous stimulation appears to consistently result in decreased short‐interval intracortical inhibition (SICI) and increased intracortical facilitation (ICF) (Aimonetti & Nielsen, 2001 ; McDonnell et al, 2007 ; Ridding et al, 2005 ; Ridding & Rothwell, 1999 ; Smith et al, 2011 ), which would seemingly oppose a net decrease in supraspinal excitability. However, as mentioned, the above studies were all performed in the distal upper limb; we are unaware of any similar investigations performed in the lower limb.…”