Biology subjects

Okamura, A. M.

Publications and source records attributed to Okamura, A. M..

4 recordsLinked to original sources

bioRxiv2020

Perspectives on the design and performance of upper-limb wearable stimulation devices for stroke survivors with hemiplegia and spasticity

BackgroundVibrotactile stimulation may improve limb function after stroke; however, current studies are limited by the stationary and clinic-based apparatus used to apply this stimulation. A wearable device could provide vibrotactile stimulation in a mobile form factor, enabling further study of this technique. ObjectiveThe aim of this work is twofold: (1) Design and validate a wearable device for stroke survivors that provides vibrotactile stimulation to the upper limb, and (2) Understand features that influence stroke survivors interaction with an upper-limb wearable device. MethodsA vibrotactile glove was designed to apply stimulation to the stroke-affected hand. This device, the vibrotactile stimulation (VTS) Glove, features small electronics, provides hours of stimulation, and has the appearance of a fingerless fitness glove. We performed two studies. In Study 1, sixteen stroke survivors were given the glove and asked to wear it for three hours daily for eight weeks. Usage time, indicating adherence, was calculated by onboard sensors. The device was evaluated using a log of damages and feedback from participants. Self-reported behaviors during glove use were also collected. In Study 2, eight stroke survivors evaluated new device prototypes in a three-round iterative design study. Interviews were used to collect participant feedback as they donned and doffed the prototypes. Task completion time and correctness were measured. Thematic content analysis was used to define actionable design revisions between each round of evaluation and identify key perspectives on design principles. ResultsThe VTS Glove is lightweight, wireless, and durable. Based on Study 1, adherence appears feasible. Each participant recorded over 140 hours wearing the VTS Glove. Participants reported wearing the glove during activities such as church, social events, dining out, and using the computer. However, 69% of participants struggled to extend or insert their fingers to don the device. Our analysis in Study 2 identified six other relevant perspectives from survivors regarding the wearable devices: hand supination is difficult, grip varies without awareness, devices may lead to sweat, separate finger attachments require dexterity, social comfort is perceived as unimportant, and the affected hand is infrequently used. New device designs with revised features (VTS Phalanx, VTS Armband, and VTS Palm) could be donned in an average time of 48 seconds (vs. 5.05 minutes to don the VTS Glove).

bioengineering↗

bioRxiv2020

Effects of Peripheral Haptic Feedback on Intracortical Brain-Computer Interface Control and Associated Sensory Responses in Motor Cortex

Intracortical brain-computer interfaces (iBCIs) provide people with paralysis a means to control devices with signals decoded from brain activity. Despite recent impressive advances, these devices still cannot approach able-bodied levels of control. To achieve naturalistic control and improved performance of neural prostheses, iBCIs will likely need to include proprioceptive feedback. With the goal of providing proprioceptive feedback via mechanical haptic stimulation, we aim to understand how haptic stimulation affects motor cortical neurons and ultimately, iBCI control. We provided skin shear haptic stimulation as a substitute for proprioception to the back of the neck of a person with tetraplegia. The neck location was determined via assessment of touch sensitivity using a monofilament test kit. The participant was able to correctly report skin shear at the back of the neck in 8 unique directions with 65% accuracy. We found motor cortical units that exhibited sensory responses to shear stimuli, some of which were strongly tuned to the stimuli and well modeled by cosine-shaped functions. We also demonstrated online iBCI cursor control with continuous skin-shear feedback driven by decoded command signals. Cursor control performance increased slightly but significantly when the participant was given haptic feedback, compared to the purely visual feedback condition.

neuroscience↗

bioRxiv2020

Teleoperation of an ankle-foot prosthesis with a wrist exoskeleton

ObjectiveWe aimed to develop a system for people with amputation that non-invasively restores missing control and sensory information for an ankle-foot prosthesis. MethodsIn our approach, a wrist exoskeleton allows people with amputation to control and receive feedback from their prosthetic ankle via teleoperation. We implemented two control schemes: position control with haptic feedback of ankle torque at the wrist; and torque control that allows the user to modify a baseline torque profile by moving their wrist against a virtual spring. We measured tracking error and frequency response for the ankle-foot prosthesis and the wrist exoskeleton. To demonstrate feasibility and evaluate system performance, we conducted an experiment in which one participant with a transtibial amputation tracked desired wrist trajectories during walking, while we measured wrist and ankle response. ResultsBenchtop testing demonstrated that for relevant walking frequencies, system error was below human perceptual error. During the walking experiment, the participant was able to voluntarily follow different wrist trajectories with an average RMS error of 1.55{degrees} after training. The ankle was also able to track desired trajectories below human perceptual error for both position control (RMSE = 0.8{degrees}) and torque control (RMSE = 8.4%). ConclusionWe present a system that allows a user with amputation to control an ankle-foot prosthesis and receive feedback about its state using a wrist exoskeleton, with accuracy comparable to biological neuromotor control. SignificanceThis bilateral teleoperation system enables novel prosthesis control and feedback strategies that could improve prosthesis control and aid motor learning.

bioengineering↗

bioRxiv2017

Simulating The Impact Of Sensorimotor Deficits On Reaching Performance

The healthy human nervous system accurately and robustly controls movements despite nonlinear dynamics, noise, and delays. After a stroke, motor ability frequently becomes impaired. To provide insight into the relative impact of specific sensorimotor deficits on motor performance, we modeled neural control of reaching with the human upper limb as a near-optimally feedback-controlled two-degree-of-freedom system with biologically based parameters. We added three sensorimotor impairments commonly associated with post-stroke hemiparesis--abnormal joint coupling, increased noise on internally modeled dynamics, and muscular weakness-- and examined the impact on reaching performance. We found that abnormal joint coupling unknown to the systems internal model caused systematic perturbations to trajectories, longer reach durations, and target overshoot. Increasing internal model noise and muscular weakness had little impact on motor performance unless model noise was increased by several orders of magnitude. Many reaches performed by our perturbed models replicate features commonly observed in reaches by hemiparetic stroke survivors. The sensitivity to unmodeled abnormal joint coupling agrees with experimental findings that abnormal coupling (possibly related to internal model errors) is the main cause of post-stroke motor impairment.

neuroscience↗