Remote vibrotactile noise improves light touch sensation in stroke survivors’ fingertips via stochastic resonance

Abstract

Background and purposeStroke rehabilitation does not often integrate both sensory and motor recovery. While subthreshold noise was shown to enhance sensory signal detection at the site of noise application, having a noise-generating device at the fingertip to enhance fingertip sensation and potentially enhance dexterity for stroke survivors is impractical, since the device would interfere with object manipulation. This study determined if remote application of subthreshold vibrotactile noise (away from the fingertips) improves fingertip tactile sensation with potential to enhance dexterity for stroke survivors.MethodsIndex finger and thumb pad sensation was measured for ten stroke survivors with fingertip sensory deficit using the Semmes-Weinstein Monofilament and Two-Point Discrimination Tests. Sensation scores were measured with noise applied at one of three intensities (40%, 60%, 80% of the sensory threshold) to one of four locations of the paretic upper extremity (dorsal hand proximal to the index finger knuckle, dorsal hand proximal to the thumb knuckle, dorsal wrist, volar wrist) in a random order, as well as without noise at beginning (Pre) and end (Post) of the testing session.ResultsVibrotactile noise of all intensities and locations instantaneously and significantly improved Monofilament scores of the index fingertip and thumb tip (p < .01). No significant effect of the noise was seen for the Two-Point Discrimination Test scores.ConclusionsRemote application of subthreshold (imperceptible) vibrotactile noise at the wrist and dorsal hand instantaneously improved stroke survivors’ light touch sensation, independent of noise location and intensity. Vibrotactile noise at the wrist and dorsal hand may have enhanced the fingertips’ light touch sensation via stochastic resonance and interneuronal connections. While long-term benefits of noise in stroke patients warrants further investigation, this result demonstrates potential that a wearable device applying vibrotactile noise at the wrist could enhance sensation and grip ability without interfering with object manipulation in everyday tasks.

An MRI-compatible hand sensory vibrotactile system

“…In order to avoid extra complications due to the MRI-compatibility requirement, the system was set up so that the noise source (audio file on a laptop, a 10 Hz to 1 kHz random noise, which was created by LabVIEW and was found effective in enhancing fingertip tactile sensation in Enders et al 2013) and the driving circuit (noise amplifier) were located outside of the MRI room, with shielded wires running into the MRI room. The BNC connector was chosen to connect to the interface panel that separates the MR room from the computer control room.…”

“…In lieu of the direct noise, vibrotactile noise applied remotely from the fingertip, such as to the wrist, was recently shown to have a promise to enhance fingertip tactile sensation (Enders et al 2013) and hand dexterity (Kosmopoulos et al 2014). It is postulated that the noise from the wrist may be integrated with the signal from the fingertip within the central nervous system, through existing nerve connections (Merzenich et al 1983; Bjorkman et al 2004; Hidaka et al 2000).…”

“… Recently, application of vibrotactile noise to the wrist or back of the hand has been shown to enhance fingertip tactile sensory perception (Enders et al 2013), supporting a potential for an assistive device worn at the wrist, that generates minute vibration to help the elderly or patients with sensory deficit. However, knowledge regarding the detailed physiological mechanism behind this sensory improvement in the central nervous system, especially in the human brain, is limited, hindering progress in development and use of such assistive devices.…”

The extent of altered digit force direction correlates with clinical upper extremity impairment in chronic stroke survivors

“…This knowledge encourages development of assistive devices or targeted therapies to improve digit force direction and thus hand function. For instance, to compensate for impaired somatosensation post stroke, sensory enhancement techniques (Conforto et al, 2007; Enders et al, 2013; Kurita et al, 2013) or visual feedback (Ellis et al, 2005; Seo et al, 2011a) may be used to improve hand function. Correcting digit force direction or muscle activation pattern using neuromuscular electrical stimulation and muscle strengthening (Santos et al, 2006; Dean et al, 2007) may directly help improve hand grip function.…”

Validation of a Vibrotactile Stimulation System Using the Wii Remote for Studies of Tactile Sensitivity

“…Several systems have been developed to generate vibrotactile stimuli, including a motor for repeated touch stimulation [6,7], a moving magnet linear actuator [8], a voice coil actuator [9], and a piezoelectric actuator [10 -12]. In addition, several mechanical stimulators are commercially available.…”