Novel Sensory Rehabilitation Paradigm Using Low-Level Vibration Applied to Wrist Skin

RESEARCH PURPOSE/HYPOTHESIS: This purpose of this study was to understand the neurobiological basis of the way enhanced finger sensation is achieved with wrist vibration. The hypothesis was that cortical sensing activity for fingertip touch stimuli increases with wrist vibration.

RATIONALE: There is a paucity of sensory rehabilitation protocols. Recent studies have shown that low-level (below-perceptible) skin vibration applied to the wrist can enhance finger touch sensation and manual dexterity in chronic stroke survivors as well as healthy adults. These studies have suggested a potential for a wearable vibrating wristband that provides sensory stimulation for enhanced sensation and dexterity of the fingers for activities of daily living.

Nonetheless, the neurobiological bases for wrist vibration–induced sensory enhancement are yet poorly understood, limiting its translation to clinical practice. Knowledge of the neurobiological bases can enable optimization of the vibration parameters for maximal benefits for individual patients as well as identification of patients who will be responsive to the intervention.

DESIGN: Repeated-measures design. Two vibration conditions (with vs. without wrist vibration) were tested for all participants.

PARTICIPANTS: Eleven adults without neurologic disorders participated to establish a normal cortical response to the vibration as the first step.

METHOD: Electroencephalogram (EEG) signals were recorded during fingertip touch stimuli using actiCAP (Brain Products, Germany). The index fingertip received passive touch by a monofilament that was controlled by a computer. Trials with and without wrist vibration were randomly ordered in blocks of 25 trials, for a total of 200 trials (100 trials per vibration condition) for each participant. Wrist vibration was delivered using C-3 Tactor (Engineering Acoustics, Inc., Casselberry, FL) taped on the volar aspect of the wrist. Vibration intensity was adjusted to 40% below sensory threshold at the wrist.

ANALYSIS: EEG data were processed using MATLAB (The MathWorks, Natick, MA) and EEGLAB toolbox. Independent-component analysis was performed to remove artifacts using the ADJUST algorithm. Then, data were divided into epochs (–100 to 600 ms relative to the fingertip touch event). Peak-to-peak somatosensory evoked potentials averaged for 100 epochs were computed for each vibration condition.

RESULTS: The peak-to-peak somatosensory evoked potential was greater with wrist vibration than without (p = .01 from signed-rank test, which is a nonparametric equivalent of the paired t test), indicating that wrist vibration increased cortical sensing activity for fingertip touch.

DISCUSSION: The result of this study suggests that wrist vibration may enhance sensory experience with fingers during activities of daily living. It is possible that this increased cortical sensing activity with vibration may facilitate neural plasticity. Because sensation is critical for dexterous hand function, enhanced sensation may also assist with restoration of dexterous hand function in those with upper-extremity sensorimotor deficits. The EEG assessment could potentially be used as an initial screening method to predict patients’ responsiveness to the vibration intervention. A low-cost and low-risk wearable vibrating wristband may be developed to assist with future usage.

IMPACT STATEMENT: This study provides the neurobiological basis for use of low-level wrist vibration in rehabilitation for those with sensorimotor deficits. Vibration may complement occupational therapy by providing patients with enhanced sensory experience during therapy for better sensorimotor outcomes.