Development and Validation of a Wearable Device to Provide Rich Somatosensory Feedback for Rehabilitation After Sensorimotor Impairment

BACKGROUNDThis study describes the development and validation of a non-invasive wearable device to provide haptic feedback and train sensory discrimination. The ultimate aim of this device is to be used as part of a treatment for functional and/or pain rehabilitation due to sensorimotor impairment.METHODSThe development was guided by a structured design control process to ensure the verifiability and validity of the design outcomes. Two sub-systems were designed to systematically provide various types of somatosensory stimulation: 1) a tactile display for touch and vibration, and 2) a set of bands for sliding, pressure, and strain sensations. The device was designed with a versatile structure that allows for its application on different body parts. We designed an interactive computer program to command the device and enable training sessions. The validation of the device was performed with 11 able-bodied individuals whose upper arm tactile sensitivity was measured over 5 training sessions conducted daily. Tactile discrimination and perception threshold were measured using the standard 2-point discrimination and Semmes-Weinstein monofilament tests, respectively.RESULTSThe development and verification procedures ensured that the device successfully complied with the pre-established requirements, which were selected to enable the device clinical application. The results on tactile discrimination and sensitivity showed high subject-dependent variability but trended towards improvement (p=0.05). This trend was also confirmed by the scores achieved during the training sessions.CONCLUSIONSWe introduced a wearable device to deliver somatosensory stimulation and to train sensory discrimination. The design is versatile enough to allow for its application on different body parts. The device was found robust enough for clinical application, and it showed to increase tactile sensitivity on upper arms of able-bodied individuals. Further studies will be conducted to determine if our current findings transfer to individuals with sensorimotor impairment and if this approach is suitable for functional and/or pain rehabilitation after sensorimotor impairments.

Chronic stroke sensorimotor impairment is related to smaller hippocampal volumes: An ENIGMA analysis

Persistent sensorimotor impairments after stroke can negatively impact quality of life. The hippocampus is involved in sensorimotor behavior but has not been widely studied within the context of post-stroke upper limb sensorimotor impairment. The hippocampus is vulnerable to secondary degeneration after stroke, and damage to this region could further weaken sensorimotor circuits, leading to greater chronic sensorimotor impairment. The purpose of this study was to investigate the cross-sectional association between non-lesioned hippocampal volume and upper limb sensorimotor impairment in people with chronic stroke. We hypothesized that smaller ipsilesional hippocampal volumes would be associated with worse upper-limb sensorimotor impairment. Cross-sectional T1-weighted brain MRIs were pooled from 357 participants at the chronic stage after stroke (>180 days post-stroke) compiled from 18 research cohorts worldwide in the ENIGMA Stroke Recovery Working Group (age: median = 61 years, interquartile range = 18, range = 23-93; 135 women and 222 men). Sensorimotor impairment was estimated from the Fugl-Meyer Assessment of Upper Extremity scores. Robust mixed-effects linear models were used to test associations between post-stroke sensorimotor impairment and hippocampal volumes (ipsilesional and contralesional separately; Bonferroni-corrected, p-value < 0.025), controlling for age, sex, lesion volume, and lesioned hemisphere. We also performed an exploratory analysis to test whether sex differences influence the relationship between sensorimotor impairment and hippocampal volume. Upper limb sensorimotor impairment was positively associated with ipsilesional (p = 0.005; d = 0.33) but not contralesional (p = 0.96; d = 0.01) hippocampal volume, such that impairment was worse for participants with smaller ipsilesional hippocampal volume. This association remained significant independent of lesion volume or other covariates (p = 0.001; d = 0.36). Evidence indicates an interaction between sensorimotor impairment and sex for both ipsilesional (p = 0.008; d = -0.29) and contralesional (p = 0.006; d = -0.30) hippocampal volumes, whereby women showed progressively worsening sensorimotor impairment with smaller hippocampal volumes compared to men. The present study has identified a novel association between chronic post-stroke sensorimotor impairment and ipsilesional, but not contralesional, hippocampal volume. This finding was not due to lesion size and may be stronger in women. We also provide supporting evidence that smaller hippocampal volume post-stroke is likely a consequence of ipsilesional damage, which could provide a link between vascular disease and other disorders, such as dementia.

Mild Stroke Affects Pointing Movements Made in Different Frames of Reference

Background Motor performance is a complex process controlled in task-specific spatial frames of reference (FRs). Movements can be made within the framework of the body (egocentric FR) or external space (exocentric FR). People with stroke have impaired reaching, which may be related to deficits in movement production in different FRs. Objective To characterize rapid motor responses to changes in the number of degrees of freedom for movements made in different FRs and their relationship with sensorimotor and cognitive impairment in individuals with mild chronic stroke. Methods Healthy and poststroke individuals moved their hand along the contralateral forearm (egocentric task) and between targets in the peripersonal space (exocentric task) without vision while flexing the trunk. Trunk movement was blocked in randomized trials. Results For the egocentric task, controls produced the same endpoint trajectories in both conditions (free- and blocked-trunk) by preserving similar shoulder-elbow interjoint coordination (IJC). However, endpoint trajectories were dissimilar because of altered IJC in stroke. For the exocentric task, controls produced the same endpoint trajectories when the trunk was free or blocked by rapidly changing the IJC, whereas this was not the case in stroke. Deficits in exocentric movement after stroke were related to cognitive but not sensorimotor impairment. Conclusions Individuals with mild stroke have deficits rapidly responding to changing conditions for complex reaching tasks. This may be related to cognitive deficits and limitations in the regulation of tonic stretch reflex thresholds. Such deficits should be considered in rehabilitation programs encouraging the reintegration of the affected arm into activities of daily living.

Sensorimotor impairment and haptic support in microgravity

Future space missions envisage human operators teleoperating robotic systems from orbital spacecraft. A potential risk for such missions is the observation that sensorimotor performance deteriorates during spaceflight. This article describes an experiment on sensorimotor performance in two-dimensional manual tracking during different stages of a space mission. We investigated whether there are optimal haptic settings of the human-machine interface for microgravity conditions. Two empirical studies using the same task paradigm with a force feedback joystick with different haptic settings (no haptics, four spring stiffnesses, two motion dampings, three masses) are presented in this paper. (1) A terrestrial control study ($$N=20$$ N = 20 subjects) with five experimental sessions to explore potential learning effects and interactions with haptic settings. (2) A space experiment ($$N=3$$ N = 3 cosmonauts) with a pre-mission, three mission sessions on board the ISS (2, 4, and 6 weeks in space), and a post-mission session. Results provide evidence that distorted proprioception significantly affects motion smoothness in the early phase of adaptation to microgravity, while the magnitude of this effect was moderated by cosmonauts’ sensorimotor capabilities. Moreover, this sensorimotor impairment can be compensated by providing subtle haptic cues. Specifically, low damping improved tracking smoothness for both motion directions (sagittal and transverse motion plane) and low stiffness improved performance in the transverse motion plane.