A "matched" sensory reference can guide goal-directed movements of the affected hand in central post-stroke sensory ataxia

Influence of vibrotactile random noise on the smoothness of the grasp movement in patients with chemotherapy-induced peripheral neuropathy

Patients with chemotherapy-induced peripheral neuropathy (CIPN) often suffer from sensorimotor dysfunction of the distal portion of the extremities (e.g., loss of somatosensory sensation, numbness/tingling, difficulty typing on a keyboard, or difficulty buttoning/unbuttoning a shirt). The present study aimed to reveal the effects of subthreshold vibrotactile random noise stimulation on sensorimotor dysfunction in CIPN patients without exacerbating symptoms. Twenty-five patients with CIPN and 28 age-matched healthy adults participated in this study. To reveal the effects of subthreshold vibrotactile random noise stimulation on sensorimotor function, participants were asked to perform a tactile detection task and a grasp movement task during random noise stimulation delivered to the volar and dorsal wrist. We set three intensity conditions of the vibrotactile random noise: 0, 60, and 120% of the sensory threshold (Noise 0%, Noise 60%, and Noise 120% conditions). In the tactile detection task, a Semmes-Weinstein monofilament was applied to the volar surface of the tip of the index finger using standard testing measures. In the grasp movement task, the distance between the thumb and index finger was recorded while the participant attempted to grasp a target object, and the smoothness of the grasp movement was quantified by calculating normalized jerk in each experimental condition. The experimental data were compared using two-way repeated-measures analyses of variance with two factors: experimental condition (Noise 0, 60, 120%) × group (Healthy controls, CIPN patients). The tactile detection threshold and the smoothness of the grasp movement were only improved in the Noise 60% condition without exacerbating numbness/tingling in CIPN patients and healthy controls. The current study suggested that the development of treatment devices using stochastic resonance can improve sensorimotor function for CIPN patients.

A hypothetical explanatory sensorimotor model of bilateral limb interference

Goal-directed movements of a limb are optimized by sensorimotor integration, a process that merges both sensory and motor representations. In a previous study, we revealed that abnormal sensory representation can impair reach-to-grasp movements in patients with spinothalamocortical pathway lesions. This abnormal motor control was significantly recovered when referencing correct somatosensory information with the intact hand. Furthermore, motor control of the intact hand was impaired when referencing abnormal somatosensory information with the affected hand. Such bilateral limb interference suggests that there is only one common integrated sensory representation and only one common motor representation for both hands. The single sensory representation would be integrated from the somatosensory information received from both hands. Subsequently, the integrated motor representation would be derived from the integrated sensory representation, and would then be split and sent out via motor commands to both hands. Considering that bimanual coordinated movements are reportedly smoother than unimanual movements, information transfer between the integrated sensory and the integrated motor representation would be suitable for such efficient bimanual movements. Therefore, we propose a novel hypothetical model to better explain the observation of bilateral limb interference. The proposed model might contribute to the development of novel sensory and motor rehabilitation strategies by promoting the use of the unaffected hand.