Evaluation of a Chair-Mounted Passive Trunk Orthosis: A Pilot Study on Able-Bodied Subjects

Trunk stability is important for adequate arm function due to their kinematic linkage. People with Duchenne muscular dystrophy (DMD) can benefit from trunk-assistive devices for seated daily activities, but existing devices limit trunk movement to forward bending. We developed a new trunk orthosis that has spring and pulley design. This study evaluated orthosis performance with 40 able-bodied subjects under with and without orthosis condition in 20 seated tasks for trunk rotation, forward bending, and side bending movements. Subjects adopted static posture in specific trunk orientation while their muscle activity was recorded. They also rated the subjective scales of perceived exertion and usability. A percent change in muscle activity for each task, due to orthosis use, is reported. Significant muscle activity reductions up to 31% and 65% were observed in lumbar and thoracic erector spinae muscles, respectively. Using three-way ANOVA, we found these reductions to be specific to the task direction and the choice of upper limb that is used to perform the asymmetric tasks. A total of 70% participants reported acceptable usability and ~1-point increase in exertion was found for maximum voluntary reaching with the orthosis. The outcomes of this study are promising, though tested on able-bodied subjects. Hence, orthosis mounted on wheelchairs should be further evaluated on DMD patients.

Does exposure to startle impact voluntary reaching movements in individuals with severe-to-moderate stroke?

When movements of individuals with stroke (iwS) are elicited by startling acoustic stimulus (SAS), reaching movements are faster, further, and directed away from the body. However, these startle-evoked movements also elicit task-inappropriate flexor activity, raising concerns that chronic exposure to startle might also induce heightened flexor activity during voluntarily elicited movement. The objective of this study is to evaluate the impact of startle exposure on voluntary movements during point-to-point reaching in individuals with moderate and severe stroke. We hypothesize that startle exposure will increase task-inappropriate activity in flexor muscles, which will be associated with worse voluntarily initiated reaching performance (e.g. decreased distance, displacement, and final accuracy). Eleven individuals with moderate-to-severe stroke (UEFM = 8–41/66 and MAS = 0–4/4) performed voluntary point-to-point reaching with 1/3 of trials elicited by an SAS. We used electromyography to measure activity in brachioradialis (BR), biceps (BIC), triceps lateral head (TRI), pectoralis (PEC), anterior deltoid (AD), and posterior deltoid (PD). Conversely to our hypothesis, exposure to startle did not increase abnormal flexion but rather antagonist activity in the elbow flexors and shoulder horizontal adductors decreased, suggesting that abnormal flexor/extensor co-contraction was reduced. This reduction of flexion led to increased reaching distance (18.2% farther), movement onset (8.6% faster), and final accuracy (16.1% more accurate) by the end of the session. This study offers the first evidence that exposure to startle in iwS does not negatively impact voluntary movement; moreover, exposure may improve volitionally activated reaching movements by decreasing abnormal flexion activity.

Attenuation of visual reafferent signals in the parietal cortex during voluntary movement

It is well established that the cortical processing of somatosensory and auditory signals is attenuated when they result from self-generated actions compared with external events. This phenomenon is thought to result from an efference copy of motor commands used to predict the sensory consequences of an action through a forward model. The present work examined whether attenuation also takes place for visual reafferent signals from the moving limb during voluntary reaching movements. To address this issue, EEG activity was recorded in a condition in which visual feedback of the hand was provided in real time and compared with a condition in which it was presented with a 150-ms delay, thus creating a mismatch between the predicted and actual visual consequences of the movement. Results revealed that the amplitude of the N1 component of the visual event-related potential evoked by hand visual feedback over the parietal cortex was significantly smaller when presented in real time compared with when it was delayed. These data suggest that the cortical processing of visual reafferent signals is attenuated when they are correctly predicted, likely as a result of a forward model.

BCI-Triggered functional electrical stimulation therapy for upper limb

We present here the integration of brain-computer interfacing (BCI) technology with functional electrical stimulation therapy to restore voluntary function. The system was tested with a single man with chronic (6 years) severe left hemiplegia resulting from a stroke. The BCI, implemented as a simple “brain-switch” activated by power decreases in the 18 Hz – 28 Hz frequency range of the participant’s electroencephalograpic signals, triggered a neuroprosthesis designed to facilitate forward reaching, reaching to the mouth, and lateral reaching movements. After 40 90-minute sessions in which the participant attempted the reaching tasks repeatedly, with the movements assisted by the BCI-triggered neuroprosthesis, the participant’s arm function showed a clinically significant six point increase in the Fugl-Meyer Asessment Upper Extermity Sub-Score. These initial results suggest that the combined use of BCI and functional electrical stimulation therapy may restore voluntary reaching function in individuals with chronic severe hemiplegia for whom the rehabilitation alternatives are very limited.

Evidence for a reference frame transformation of vestibular signal contributions to voluntary reaching

To contribute appropriately to voluntary reaching during body motion, vestibular signals must be transformed from a head-centered to a body-centered reference frame. We quantitatively investigated the evidence for this transformation during online reach execution by using galvanic vestibular stimulation (GVS) to simulate rotation about a head-fixed, roughly naso-occipital axis as human subjects made planar reaching movements to a remembered location with their head in different orientations. If vestibular signals that contribute to reach execution have been transformed from a head-centered to a body-centered reference frame, the same stimulation should be interpreted as body tilt with the head upright but as vertical-axis rotation with the head inclined forward. Consequently, GVS should perturb reach trajectories in a head-orientation-dependent way. Consistent with this prediction, GVS applied during reach execution induced trajectory deviations that were significantly larger with the head forward compared with upright. Only with the head forward were trajectories consistently deviated in opposite directions for rightward versus leftward simulated rotation, as appropriate to compensate for body vertical-axis rotation. These results demonstrate that vestibular signals contributing to online reach execution have indeed been transformed from a head-centered to a body-centered reference frame. Reach deviation amplitudes were comparable to those predicted for ideal compensation for body rotation using a biomechanical limb model. Finally, by comparing the effects of application of GVS during reach execution versus prior to reach onset we also provide evidence that spatially transformed vestibular signals contribute to at least partially distinct compensation mechanisms for body motion during reach planning versus execution.