A roadmap for implanting microelectrode arrays to evoke tactile sensations through intracortical microstimulation.

Intracortical microstimulation (ICMS) is a method for restoring sensation to people with paralysis as part of a bidirectional brain-computer interface to restore upper limb function. Evoking tactile sensations of the hand through ICMS requires precise targeting of implanted electrodes. Here we describe the presurgical imaging procedures used to generate functional maps of the hand area of the somatosensory cortex and subsequent planning that guided the implantation of intracortical microelectrode arrays. In five participants with cervical spinal cord injury, across two study locations, this procedure successfully enabled ICMS-evoked sensations localized to at least the first four digits of the hand. The imaging and planning procedures developed through this clinical trial provide a roadmap for other brain-computer interface studies to ensure successful placement of stimulation electrodes.

Motor cortex retains and reorients neural dynamics during motor imagery.

The most prominent characteristic of motor cortex is its activation during movement execution, but it is also active when we simply imagine movements in the absence of actual motor output. Despite decades of behavioural and imaging studies, it is unknown how the specific activity patterns and temporal dynamics in motor cortex during covert motor imagery relate to those during motor execution. Here we recorded intracortical activity from the motor cortex of two people who retain some residual wrist function following incomplete spinal cord injury as they performed both actual and imagined isometric wrist extensions. We found that we could decompose the population activity into three orthogonal subspaces, where one was similarly active during both action and imagery, and the others were active only during a single task type-action or imagery. Although they inhabited orthogonal neural dimensions, the action-unique and imagery-unique subspaces contained a strikingly similar set of dynamic features. Our results suggest that during motor imagery, motor cortex maintains the same overall population dynamics as during execution by reorienting the components related to motor output and/or feedback into a unique, output-null imagery subspace.

Residential Mobility and Reasons for Moving Among People Living With Spinal Cord Injury: Results of a Multisite Survey Study.

Background: Residential mobility after spinal cord injury (SCI) has not been extensively examined despite a growing interest in investigating the relationship between neighborhood exposures and community living outcomes. Objectives: This study explores residential mobility patterns, the annual move rate, and reasons for moving among a community-living sample of adults with SCI. Methods: A survey was conducted with 690 people at six SCI Model Systems centers in the United States between July 2017 and October 2020. The outcomes included move status in the past 12 months, move distance, and the primary reason for moving. A sample from the 2019 American Community Survey (ACS) 5-year pooled estimates was obtained for comparative analysis. Descriptive statistics were used to summarize the distributions of the outcomes and differences between the samples. Results: The annual move rate for adults with SCI was 16.4%, and most moves were within the same county (56.6%). Recent movers were more likely to be young adults, be newly injured, and have low socioeconomic status. Housing quality, accessibility, and family were more frequently reported motivations for moving compared to employment. Young adults more commonly moved for family and accessibility, whereas middle-aged adults more commonly moved for housing quality. No notable difference was observed in the annual move rate between the SCI and the general population samples. Conclusion: These findings suggest an age-related pattern of residential relocation after SCI, which may be indicative an extended search for optimal living conditions that meet the housing and accessibility needs of this population.

Restoration of sensory feedback from the foot and reduction of phantom limb pain via closed-loop spinal cord stimulation.

Restoring somatosensory feedback in individuals with lower-limb amputations would reduce the risk of falls and alleviate phantom limb pain. Here we show, in three individuals with transtibial amputation (one traumatic and two owing to diabetic peripheral neuropathy), that sensations from the missing foot, with control over their location and intensity, can be evoked via lateral lumbosacral spinal cord stimulation with commercially available electrodes and by modulating the intensity of stimulation in real time on the basis of signals from a wireless pressure-sensitive shoe insole. The restored somatosensation via closed-loop stimulation improved balance control (with a 19-point improvement in the composite score of the Sensory Organization Test in one individual) and gait stability (with a 5-point improvement in the Functional Gait Assessment in one individual). And over the implantation period of the stimulation leads, the three individuals experienced a clinically meaningful decrease in phantom limb pain (with an average reduction of nearly 70% on a visual analogue scale). Our findings support the further clinical assessment of lower-limb neuroprostheses providing somatosensory feedback.

Changes in neuromuscular activation, heart rate and rate of perceived exertion over the course of a wheelchair propulsion fatigue protocol.

Shoulder pain is common in persons with spinal cord injury and has been associated with wheelchair use. Fatigue related compensation strategies have been identified as possibly impacting the development of shoulder injury and pain. The purpose of this study was to investigate the progression of performance fatigability (i.e., decline in objective measure of performance including neuromuscular activation and increase in heart rate) and perceived fatigability (i.e., increased perceived exertion) during a 15-min fatigue protocol including maximum voluntary overground wheelchair propulsion. Fifty participants with paraplegic spinal cord injury completed three 4-min rounds of wheelchair propulsion, separated by 90 s of rest, on a figure-8 course consisting of two turns and full stops per lap in their manual wheelchairs (ClinicalTrials.gov: NCT03153033). Electromyography (EMG) signal of five muscles acting on the shoulder joint, heart rate (HR), and rate of perceived exertion (RPE) were measured at the beginning and end of every 4 min of propulsion. Root Mean Square (RMS) and Mean Power Frequency were calculated from EMG data. There was a significant increase in %RMS of the pectoralis major pars sternalis and trapezius pars descendens, HR, and RPE with greatest changes during the first 4 min of the protocol. The observed changes in neuromuscular activation in only two of the shoulder muscles may impact muscular imbalances and the development of shoulder injuries and should be further studied. The current study gives clearer insight into the mechanisms of performance fatigability and perceived fatigability throughout a wheelchair propulsion fatigue protocol.

Microstimulation of human somatosensory cortex evokes task-dependent, spatially patterned responses in motor cortex.

The primary motor (M1) and somatosensory (S1) cortices play critical roles in motor control but the signaling between these structures is poorly understood. To fill this gap, we recorded - in three participants in an ongoing human clinical trial (NCT01894802) for people with paralyzed hands - the responses evoked in the hand and arm representations of M1 during intracortical microstimulation (ICMS) in the hand representation of S1. We found that ICMS of S1 activated some M1 neurons at short, fixed latencies consistent with monosynaptic activation. Additionally, most of the ICMS-evoked responses in M1 were more variable in time, suggesting indirect effects of stimulation. The spatial pattern of M1 activation varied systematically: S1 electrodes that elicited percepts in a finger preferentially activated M1 neurons excited during that finger's movement. Moreover, the indirect effects of S1 ICMS on M1 were context dependent, such that the magnitude and even sign relative to baseline varied across tasks. We tested the implications of these effects for brain-control of a virtual hand, in which ICMS conveyed tactile feedback. While ICMS-evoked activation of M1 disrupted decoder performance, this disruption was minimized using biomimetic stimulation, which emphasizes contact transients at the onset and offset of grasp, and reduces sustained stimulation.

Tessellation of artificial touch via microstimulation of human somatosensory cortex.

When we interact with objects, we rely on signals from the hand that convey information about the object and our interaction with it. A basic feature of these interactions, the locations of contacts between the hand and object, is often only available via the sense of touch. Information about locations of contact between a brain-controlled bionic hand and an object can be signaled via intracortical microstimulation (ICMS) of somatosensory cortex (S1), which evokes touch sensations that are localized to a specific patch of skin. To provide intuitive location information, tactile sensors on the robotic hand drive ICMS through electrodes that evoke sensations at skin locations matching sensor locations. This approach requires that ICMS-evoked sensations be focal, stable, and distributed over the hand. To systematically investigate the localization of ICMS-evoked sensations, we analyzed the projected fields (PFs) of ICMS-evoked sensations - their location and spatial extent - from reports obtained over multiple years from three participants implanted with microelectrode arrays in S1. First, we found that PFs vary widely in their size across electrodes, are highly stable within electrode, are distributed over large swaths of each participant's hand, and increase in size as the amplitude or frequency of ICMS increases. Second, while PF locations match the locations of the receptive fields (RFs) of the neurons near the stimulating electrode, PFs tend to be subsumed by the corresponding RFs. Third, multi-channel stimulation gives rise to a PF that reflects the conjunction of the PFs of the component channels. By stimulating through electrodes with largely overlapping PFs, then, we can evoke a sensation that is experienced primarily at the intersection of the component PFs. To assess the functional consequence of this phenomenon, we implemented multichannel ICMS-based feedback in a bionic hand and demonstrated that the resulting sensations are more localizable than are those evoked via single-channel ICMS.

Biomimetic multi-channel microstimulation of somatosensory cortex conveys high resolution force feedback for bionic hands.

Manual interactions with objects are supported by tactile signals from the hand. This tactile feedback can be restored in brain-controlled bionic hands via intracortical microstimulation (ICMS) of somatosensory cortex (S1). In ICMS-based tactile feedback, contact force can be signaled by modulating the stimulation intensity based on the output of force sensors on the bionic hand, which in turn modulates the perceived magnitude of the sensation. In the present study, we gauged the dynamic range and precision of ICMS-based force feedback in three human participants implanted with arrays of microelectrodes in S1. To this end, we measured the increases in sensation magnitude resulting from increases in ICMS amplitude and participant's ability to distinguish between different intensity levels. We then assessed whether we could improve the fidelity of this feedback by implementing "biomimetic" ICMS-trains, designed to evoke patterns of neuronal activity that more closely mimic those in natural touch, and by delivering ICMS through multiple channels at once. We found that multi-channel biomimetic ICMS gives rise to stronger and more distinguishable sensations than does its single-channel counterpart. Finally, we implemented biomimetic multi-channel feedback in a bionic hand and had the participant perform a compliance discrimination task. We found that biomimetic multi-channel tactile feedback yielded improved discrimination over its single-channel linear counterpart. We conclude that multi-channel biomimetic ICMS conveys finely graded force feedback that more closely approximates the sensitivity conferred by natural touch.

Motor cortex retains and reorients neural dynamics during motor imagery.

The most prominent role of motor cortex is generating patterns of neural activity that lead to movement, but it is also active when we simply imagine movements in the absence of actual motor output. Despite decades of behavioral and imaging studies, it is unknown how the specific activity patterns and temporal dynamics within motor cortex during covert motor imagery relate to those during motor execution. Here we recorded intracortical activity from the motor cortex of two people with residual wrist function following incomplete spinal cord injury as they performed both actual and imagined isometric wrist extensions. We found that we could decompose the population-level activity into orthogonal subspaces such that one set of components was similarly active during both action and imagery, and others were only active during a single task typeâ€"action or imagery. Although they inhabited orthogonal neural dimensions, the action-unique and imagery-unique subspaces contained a strikingly similar set of dynamical features. Our results suggest that during motor imagery, motor cortex maintains the same overall population dynamics as during execution by recreating the missing components related to motor output and/or feedback within a unique imagery-only subspace.

Amputee, clinician, and regulator perspectives on current and prospective upper extremity prosthetic technologies.

Existing prosthetic technologies for people with upper limb amputation are being adopted at moderate rates. Once fitted for these devices, many upper limb amputees report not using them regularly or at all. The primary aim of this study was to solicit feedback about prosthetic technology and important device design criteria from amputees, clinicians, and device regulators. We compare these perspectives to identify common or divergent priorities. Twenty-one adults with upper limb loss, 35 clinicians, and 3 regulators completed a survey on existing prosthetic technologies and a conceptual sensorimotor prosthesis driven by implanted myoelectric electrodes with sensory feedback via spinal root stimulation. The survey included questions from the Trinity Amputation and Prosthesis Experience Scale, the Disabilities of the Arm, Shoulder, and Hand, and novel questions about technology acceptance and neuroprosthetic design. User and clinician ratings of satisfaction with existing devices were similar. Amputees were most accepting of the proposed sensorimotor prosthesis (75.5% vs clinicians (68.8%), regulators (67.8%)). Stakeholders valued user-centered outcomes like individualized task goals, improved quality of life, device reliability, and user safety; regulators emphasized these last two. The results of this study provide insight into amputee, clinician, and regulator priorities to inform future upper-limb prosthetic design and clinical trial protocol development.

Limb accelerations during sleep are related to measures of strength, sensation, and spasticity among individuals with spinal cord injury.

BACKGROUND: To evaluate the relationship between measures of neuromuscular impairment and limb accelerations (LA) collected during sleep among individuals with chronic spinal cord injury (SCI) to provide evidence of construct and concurrent validity for LA as a clinically meaningful measure. METHODS: The strength (lower extremity motor score), sensation (summed lower limb light touch scores), and spasticity (categorized lower limb Modified Ashworth Scale) were measured from 40 adults with chronic (≥ 1 year) SCI. Demographics, pain, sleep quality, and other covariate or confounding factors were measured using self-report questionnaires. Each participant then wore ActiGraph GT9X Link accelerometers on their ankles and wrist continuously for 1-5 days to measure LA from movements during sleep. Regression models with built-in feature selection were used to determine the most relevant LA features and the association to each measure of impairment. RESULTS: LA features were related to measures of impairment with models explaining 69% and 73% of the variance (R²) in strength and sensation, respectively, and correctly classifying 81.6% (F1-score = 0.814) of the participants into spasticity categories. The most commonly selected LA features included measures of power and frequency (frequency domain), movement direction (correlation between axes), consistency between movements (relation to recent movements), and wavelet energy (signal characteristics). Rolling speed (change in angle of inclination) and movement smoothness (median crossings) were uniquely associated with strength. When LA features were included, an increase of 72% and 222% of the variance was explained for strength and sensation scores, respectively, and there was a 34% increase in spasticity classification accuracy compared to models containing only covariate features such as demographics, sleep quality, and pain. CONCLUSION: LA features have shown evidence of having construct and concurrent validity, thus demonstrating that LA are a clinically-relevant measure related to lower limb strength, sensation, and spasticity after SCI. LA may be useful as a more detailed measure of impairment for applications such as clinical prediction models for ambulation.

Closed-loop stimulation of lateral cervical spinal cord in upper-limb amputees to enable sensory discrimination: a case study.

Modern myoelectric prosthetic hands have multiple independently controllable degrees of freedom, but require constant visual attention to use effectively. Somatosensory feedback provides information not available through vision alone and is essential for fine motor control of our limbs. Similarly, stimulation of the nervous system can potentially provide artificial somatosensory feedback to reduce the reliance on visual cues to efficiently operate prosthetic devices. We have shown previously that epidural stimulation of the lateral cervical spinal cord can evoke tactile sensations perceived as emanating from the missing arm and hand in people with upper-limb amputation. In this case study, two subjects with upper-limb amputation used this somatotopically-matched tactile feedback to discriminate object size and compliance while controlling a prosthetic hand. With less than 30 min of practice each day, both subjects were able to use artificial somatosensory feedback to perform a subset of the discrimination tasks at a success level well above chance. Subject 1 was consistently more adept at determining object size (74% accuracy; chance: 33%) while Subject 2 achieved a higher accuracy level in determining object compliance (60% accuracy; chance 33%). In each subject, discrimination of the other object property was only slightly above or at chance level suggesting that the task design and stimulation encoding scheme are important determinants of which object property could be reliably identified. Our observations suggest that changes in the intensity of artificial somatosensory feedback provided via spinal cord stimulation can be readily used to infer information about object properties with minimal training.

Effect of Fatiguing Wheelchair Propulsion and Weight Relief Lifts on Subacromial Space in Wheelchair Users.

Objective: This study aimed to identify targets of intervention for reducing shoulder pain in wheelchair users with spinal cord injury (SCI) by (1) examining changes in subacromial space [acromiohumeral distance (AHD) and occupation ratio (OccRatio)] with fatiguing wheelchair propulsion, and different loading conditions [unloaded position vs. weight relief lifts (WRL)]; (2) associating these changes with wheelchair user capacity, as well as (3) identifying subject characteristics associated with subacromial space, such as sex, lesion level, time since injury, body mass index and impaired shoulder range of motion. Methods: Fifty manual wheelchair users with SCI [11 females, age = 50.5 (9.7) years, time since injury = 26.2 (11.4) years] participated in this quasi-experimental one-group pretest-posttest study. Ultrasound images were used to define AHD during an unloaded position, and during personal and instructed WRL before and after fatiguing wheelchair propulsion. Furthermore, supraspinatus and biceps thickness defined from ultrasound images were used to calculate OccRatios. Wheelchair user capacity was quantified as functional strength (maximum resultant force reached during maximum isometric forward push) and anaerobic work capacity (highest power output reached during 15-m sprint test). Multilevel mixed-effects linear regression analyses controlling for between subject variability and covariables were performed to address the research questions. Results: AHD was significantly smaller during personal WRL (p < 0.001) and instructed WRL (p = 0.009, AHD both 11.5 mm) compared to the unloaded position (11.9 mm). A higher wheelchair user capacity (higher anaerobic work capacity) reduced the impact of WRL on AHD decrease. The fatiguing wheelchair propulsion had no effect on AHD (p = 0.570) and on OccRatio of supraspinatus (p = 0.404) and biceps (p = 0.448). Subject characteristics related to a larger subacromial space were lower lesion level, shorter time since injury, impaired external rotation, a lower body mass index and a higher anaerobic work capacity. Conclusion: This study showed a significant reduction in AHD during WRL with no effect of fatiguing wheelchair propulsion on the subacromial space in wheelchair users with SCI. A higher anaerobic work capacity was beneficial in stabilizing the shoulder during WRL. Our findings may assist clinicians in designing a shoulder injury prevention program.

Effectiveness of Group Wheelchair Maintenance Training for People with Spinal Cord Injury: A Randomized Controlled Trial.

OBJECTIVE: To assess the effectiveness of group wheelchair maintenance training and investigate participant characteristics associated with responsiveness to training. DESIGN: Randomized controlled trial with an immediate group and a waitlist control group (WLCG) who received the intervention after a 6-month delay. SETTING: Four Spinal Cord Injury Model Systems Centers. PARTICIPANTS: Manual (MWC; n=80) and power wheelchair (PWC; n=67) users with spinal cord injury (N=147). INTERVENTIONS: Two 90-minute structured wheelchair maintenance training program classes with 12-20 people per class and separate classes for MWC and PWC users. Each class included in-person hands-on demonstrations and practice of wheelchair maintenance. MAIN OUTCOME MEASURES: Separate analysis was completed for MWC and PWC users using the Wheelchair Maintenance Training Questionnaire (WMT-Q) capacity (ability to complete), performance (frequency of completion) and knowledge at baseline, 1 month, 6 months, 6 months pretraining (WLCG only), and 1 year (immediate only). RESULTS: After the intervention, participants in both the immediate and WLCG improved in maintenance capacity (MWC and PWC, P<.001) and performance (MWC and PWC, P<.001) with training. Only PWC users improved knowledge of wheelchair maintenance (P<.001). For both WLCGs (MWC and PWC), there was no difference between the 6-month pretraining time point and baseline. MWC users who responded to training had lower WMT-Q scores for all domains, whereas this was only the case for knowledge for PWC users. CONCLUSIONS: Group wheelchair skills training is effective at improving capacity to complete maintenance and performance of maintenance activities for MWC and PWC users, even in a cohort of experienced wheelchair users. For MWC users, improvements were tied to lower WMT-Q scores at baseline, whereas PWC users improved in capacity and performance independent of baseline score. Delivering this training in a structured group format has a lower cost, which might improve adoption into clinical practice.

Changes in Internet Use Over Time Among Individuals with Traumatic Spinal Cord Injury.

OBJECTIVE: To investigate the changes in total internet and mobile internet use over time and determine how demographic characteristics are related to changes in internet and mobile internet use among individuals with spinal cord injury (SCI). DESIGN: Cross-sectional analysis of a multicenter cohort study. SETTING: National SCI Database. PARTICIPANTS: Individuals with traumatic SCI with follow-up data collected between 2012 and 2018 (N=13,622). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Proportion of sample reporting internet use at all or through a mobile device over time and specifically in 2018. RESULTS: The proportion of internet users increased from 77.7% in 2012 to 88.1% in 2018. Older participants (P<.001); those with lower annual income (P<.001), less education (P<.001), non-White race or Hispanic ethnicity (P<.001), or motor incomplete tetraplegia (P=.004); and men (P=.035) were less likely to use the internet from 2012-2018. By 2018, there were no longer differences in internet use based on race and ethnicity (P=.290) or sex (P=.066). Mobile internet use increased each year (52.4% to 87.7% of internet users from 2012-2018), with a participant being 13.7 times more likely to use mobile internet in 2018 than 2012. Older age (P<.001), income <$50,000 (P<.001), high school diploma or less (P=.011), or non-Hispanic White race/ethnicity (P=.001) were associated with less mobile internet use over time. By 2018, there were no differences in mobile internet use by education (P=.430), and only participants with incomes >$75,000 per year had greater odds of mobile internet use (P=.016). CONCLUSIONS: Disparities associated with internet access are decreasing likely as a result of mobile device use. Increased internet access offers an important opportunity to provide educational and training materials to frequently overlooked groups of individuals with SCI.

Creating a Resident Research Track in Synergy With the Rehabilitation Medicine Scientist Training Program.

ABSTRACT: Physician scientists play an important role in the translation of research findings to patient care; however, their training faces numerous challenges. Residency research track programs represent an opportunity to facilitate the training of future physician scientists in physical medicine and rehabilitation, although optimal program organization and long-term outcomes remain unknown. The Rehabilitation Medicine Scientist Training Program is a National Institutes of Health-funded program aimed at addressing the shortage of physician researchers in the field of physical medicine and rehabilitation by providing instruction, mentorship, and networking opportunities for a successful research career. While the opportunities provided through the Rehabilitation Medicine Scientist Training Program provide critical education and guidance at a national level, trainees are most successful with availability of strong local support and mentorship. The purpose of this article was to present a realistic and easily applicable structure for a physical medicine and rehabilitation residency research track that can be used in concert with the Rehabilitation Medicine Scientist Training Program.

Type and frequency of wheelchair repairs and resulting adverse consequences among veteran wheelchair users.

PURPOSE: Investigate the type and frequency of wheelchair repairs and resulting adverse consequences in a Veteran population. DESIGN: Convenience cross-sectional sample survey. SETTING: Data were collected at the 2017 National Veterans Wheelchair Games. PARTICIPANTS: Veterans who use a wheelchair ≥ 40 h/wk (n = 60). INTERVENTION: Not applicable. MAIN OUTCOME MEASURES: Repairs and associated adverse consequences, wheelchair age and usage, type of repairs completed, time elapsed between breakdowns and repairs, and who completed repairs. RESULTS: 60 participants reported 124 repairs in the previous 6 months with 88.3% of participants requiring at least one repair. Consequences were reported by 43.5% of those experiencing repairs and were most commonly secondary to repairs in the electrical system, wheelchair frame, power/control system, and wheels and casters. Travelling greater distances during the week and on weekends was associated with increased rates of repairs (p = 0.01 and p = 0.02, respectively) and consequences (p = 0.03 and p = 0.03, respectively). Power wheelchairs were more likely to require repairs than manual wheelchairs (p = 0.007). The median time to repair was 7 [0.8,30] days. Vendors completed 82.1% of the repairs. Those experiencing longer repair times were more likely to experience adverse consequences (p < 0.001). CONCLUSION: A high number of repairs and resulting adverse consequences occur for wheelchair users, particularly power wheelchair users, in a sample of Veterans. Interventions to prevent breakdowns and to address repairs and adverse consequences in a time-efficient manner are needed.Implications for rehabilitationIn a sample of Veterans, a high number of repairs and resulting adverse consequences occur for wheelchair users, particularly power wheelchair users.There is an important clinical opportunity to help wheelchair users avoid repairs in the first place and reduce adverse consequences after breakdowns occur by improving wheelchair quality, providing preventative chair maintenance, and repairing breakdowns in a timely and efficient manner.These interventions may prove impactful in reducing the adverse medical, functional, and social consequences of wheelchair breakdowns.