Use of imperceptible wrist vibration to modulate sensorimotor cortical activity

Abstract

Peripheral sensory stimulation has been used as a method to stimulate the sensorimotor cortex, with applications in neurorehabilitation. To improve delivery modality and usability, a new stimulation method has been developed in which imperceptible random-frequency vibration is applied to the wrist concurrently during hand activity. The objective of this study was to investigate effects of this new sensory stimulation on the sensorimotor cortex. Healthy adults were studied. In a transcranial magnetic stimulation (TMS) study, resting motor threshold, short-interval intracortical inhibition, and intracortical facilitation for the abductor pollicis brevis muscle were compared between vibration on vs. off, while subjects were at rest. In an electroencephalogram (EEG) study, alpha and beta power during rest and event-related desynchronization (ERD) for hand grip were compared between vibration on vs. off. Results showed that vibration decreased EEG power and decreased TMS short-interval intracortical inhibition (i.e., disinhibition) compared with no vibration at rest. Grip-related ERD was also greater during vibration, compared to no vibration. In conclusion, subthreshold random-frequency wrist vibration affected the release of intracortical inhibition and both resting and grip-related sensorimotor cortical activity. Such effects may have implications in rehabilitation.

Keywords: Brain mapping; Cortical excitability; Hand; Physical stimulation; Sensorimotor cortex; Subliminal stimulation.

Figure 1.

Setup for TMS (A) and EEG (B) experiments.

Figure 2.

Comparison between the vibration on and off conditions for the resting motor threshold (RMT) (A), short-interval intracortical inhibition (SICI) (B), and intracortical facilitation (ICF) (C). Means with SE are shown as bar graphs with error bars. Individual subjects’ data are shown as lines. (B) and (C) show conditioned MEP amplitudes expressed as % of the unconditioned MEP amplitudes. Increase in values in (B) indicates reduced inhibition. A significant difference between the vibration on and off conditions was found for SICI only (noted with * in B).

Figure 3.

The t-statistics comparing power during baseline (rest) between the vibration ‘on’ and ‘off’ conditions, for the alpha (A) and beta band (B), with the blue color indicating reduced power with vibration compared to without.

Figure 4.

The time course of event-related spectral perturbation (ERSP) is shown for the alpha (A) and beta band (B) for the two vibration conditions, with shades showing the standard error for each vibration condition. ERSP is expressed as change from the baseline power in dB. The vertical lines represent the times the grip cue was presented to the subject at 0 s and the rest cue at 2 s. ERSP time course averaged for three electrodes (FC4/C4/CP4) is shown. Topography of event-related desynchronization (ERD) is shown for the alpha (C) and beta band (D). In C & D, the first column shows the topography for grip initiation (averaged over 1 s period immediately after the cue to grip), and the second column shows the topography for grip termination (averaged over 1 s period immediately after the cue to rest). The first row shows ERD topography for the vibration off condition, the second row for the vibration on condition, and the third row for t-statistics comparing the vibration on vs. off conditions with the blue color indicating greater ERD with vibration compared to without.