Brain Mechanism for Enhanced Hand Function with Remote Sensory Stimulation

Abstract

The neurological bases for remote vibration enhanced sensory feedback and motor function are yet poorly understood. The purpose of this dissertation was to identify and examine the effect of vibration on finger tactile sensation in healthy adults and how imperceptible random vibration applied to the wrist changes cortical activity for fingertip sensation and precision grip. In a series of studies on healthy adults, white-noise vibration was applied to one of four locations (dorsum hand by the second knuckle, thenar and hypothenar areas, and volar wrist) at one of four intensities (zero, 60%, 80%, and 120% of the sensory threshold for each vibration location), while the fingertip sensation, the smallest vibratory signal that could be perceived on the thumb and index fingertip pads, was assessed. Vibration intensities significantly affected the fingertip sensation (p.01), all compared with the zero vibration condition. The next step was to examine the cortical activity for this vibration-enhanced fingertip sensation. We measured somatosensory evoked potentials to assess peak-to-peak response to light touch of the index fingertip with applied wrist vibration versus without. We observed increased peak-to-peak somatosensory evoked potentials with wrist vibration, especially with increased amplitude of the later component for the somatosensory, motor, and premotor cortex with wrist vibration. These findings corroborate an enhanced cortical-level sensory response motivated by vibration. It is possible that the cortical modulation observed here is the result of the establishment of transient networks for improved perception. Finally, we examined the effect of imperceptible vibration applied to the wrist on cortical control for precision grip. We measured β-band power to assess peak-to-peak response while subjects performed precision pinch with wrist vibration versus without. We observed increased peak-to-peak β-band power amplitude with wrist vibration, especially with event-related synchronization for the prefrontal, sensorimotor, motor, premotor, and supplementary motor areas with vibration. The enhanced motor function may possibly be a result of higher recalibration following movement and faster motor learning.