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Invasive brain-machine interfaces can help restore function through the control of external devices while the addition of intracortical microstimulation (ICMS) can elicit sensations of touch and help provide further benefits for individuals living with sensorimotor deficits. However, the extent of tactile information that can be conveyed through ICMS has not been fully explored. In a human participant with spinal cord injury and chronically implanted microelectrode arrays, we used ICMS to the somatosensory cortex to provide grip force feedback in the hands during grasping of objects with varying stiffness with a robotic arm. Using only ICMS-evoked touch sensations, the participant was able to identify between two and three objects with an accuracy of 92% and 67%, respectively. In a compliant grasping task with the goal of grasping a delicate object without crushing it, objects were deformed on average only 2.8 mm with ICMS-based touch feedback compared to 8.7 mm without. These results demonstrate that ICMS-evoked touch sensations to the hands can be used to provide force-based feedback for perceiving object properties and enable more precise grasping during closed-loop control of a robotic limb through a cortical interface.

The cerebellum has demonstrated a critical role during adaptation in motor learning. However, the extent to which it can contribute to the skill acquisition of complex real-world tasks remains unclear. One particularly challenging application in terms of motor activities is robotic surgery, which requires surgeons to complete complex multidimensional visuomotor tasks through a remotely operated robot. Given the need for high skill proficiency and the lack of haptic feedback, there is a pressing need for understanding and improving skill development. We investigated the effect of cerebellar transcranial direct current stimulation applied during the execution of a robotic surgery training task. Study participants received either real or sham stimulation while performing a needle driving task in a virtual (simulated) and a real-world (actual surgical robot) setting. We found that cerebellar stimulation significantly improved performance compared to sham stimulation at fast (more demanding) execution speeds in both virtual and real-world training settings. Furthermore, participants that received cerebellar stimulation more effectively transferred the skills they acquired during virtual training to the real world. Our findings underline the potential of non-invasive brain stimulation to enhance skill learning and transfer in real-world relevant tasks and, more broadly, its potential for improving complex motor learning., (© 2023. The Author(s).)

Advances in intelligent robotic systems and brain-machine interfaces (BMI) have helped restore functionality and independence to individuals living with sensorimotor deficits; however, tasks requiring bimanual coordination and fine manipulation continue to remain unsolved given the technical complexity of controlling multiple degrees of freedom (DOF) across multiple limbs in a coordinated way through a user input. To address this challenge, we implemented a collaborative shared control strategy to manipulate and coordinate two Modular Prosthetic Limbs (MPL) for performing a bimanual self-feeding task. A human participant with microelectrode arrays in sensorimotor brain regions provided commands to both MPLs to perform the self-feeding task, which included bimanual cutting. Motor commands were decoded from bilateral neural signals to control up to two DOFs on each MPL at a time. The shared control strategy enabled the participant to map his four-DOF control inputs, two per hand, to as many as 12 DOFs for specifying robot end effector position and orientation. Using neurally-driven shared control, the participant successfully and simultaneously controlled movements of both robotic limbs to cut and eat food in a complex bimanual self-feeding task. This demonstration of bimanual robotic system control via a BMI in collaboration with intelligent robot behavior has major implications for restoring complex movement behaviors for those living with sensorimotor deficits., Competing Interests: DH is inventor on intellectual property pertaining to robotic manipulation. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Handelman, Osborn, Thomas, Badger, Thompson, Nickl, Anaya, Wormley, Cantarero, McMullen, Crone, Wester, Celnik, Fifer and Tenore.)

Understanding the cortical representations of movements and their stability can shed light on improved brain-machine interface (BMI) approaches to decode these representations without frequent recalibration. Here, we characterize the spatial organization (somatotopy) and stability of the bilateral sensorimotor map of forearm muscles in an incomplete-high spinal-cord injury study participant implanted bilaterally in the primary motor and sensory cortices with Utah microelectrode arrays (MEAs). We built representation maps by recording bilateral multiunit activity (MUA) and surface electromyography (EMG) as the participant executed voluntary contractions of the extensor carpi radialis (ECR), and attempted motions in the flexor carpi radialis (FCR), which was paralytic. To assess stability, we repeatedly mapped and compared left- and right-wrist-extensor-related activity throughout several sessions, comparing somatotopy of active electrodes, as well as neural signals both at the within-electrode (multiunit) and cross-electrode (network) levels. Wrist motions showed significant activation in motor and sensory cortical electrodes. Within electrodes, firing strength stability diminished as the time increased between consecutive measurements (hours within a session, or days across sessions), with higher stability observed in sensory cortex than in motor, and in the contralateral hemisphere than in the ipsilateral. However, we observed no differences at network level, and no evidence of decoding instabilities for wrist EMG, either across timespans of hours or days, or across recording area. While map stability differs between brain area and hemisphere at multiunit/electrode level, these differences are nullified at ensemble level., (© 2022. The Author(s).)

Background and Objectives: The restoration of touch to fingers and fingertips is critical to achieving dexterous neuroprosthetic control for individuals with sensorimotor dysfunction. However, localized fingertip sensations have not been evoked via intracortical microstimulation (ICMS)., Methods: Using a novel intraoperative mapping approach, we implanted electrode arrays in the finger areas of left and right somatosensory cortex and delivered ICMS over a 2-year period in a human participant with spinal cord injury., Results: Stimulation evoked tactile sensations in 8 fingers, including fingertips, spanning both hands. Evoked percepts followed expected somatotopic arrangements. The subject was able to reliably identify up to 7 finger-specific sites spanning both hands in a finger discrimination task. The size of the evoked percepts was on average 33% larger than a finger pad, as assessed via manual markings of a hand image. The size of the evoked percepts increased modestly with increased stimulation intensity, growing 21% as pulse amplitude increased from 20 to 80 µA. Detection thresholds were estimated on a subset of electrodes, with estimates of 9.2 to 35 µA observed, roughly consistent with prior studies., Discussion: These results suggest that ICMS can enable the delivery of consistent and localized fingertip sensations during object manipulation by neuroprostheses for individuals with somatosensory deficits., Clinicaltrialsgov Identifier: NCT03161067., (© 2021 American Academy of Neurology.)

Advances in brain-machine interfaces have helped restore function and independence for individuals with sensorimotor deficits; however, providing efficient and effective sensory feedback remains challenging. Intracortical microstimulation (ICMS) of sensorimotor brain regions is a promising technique for providing bioinspired sensory feedback. In a human participant with chronically-implanted microelectrode arrays, we provided ICMS to the primary somatosensory cortex to generate tactile percepts in his hand. In a 3-choice object identification task, the participant identified virtual objects using tactile sensory feedback and no visual information. We evaluated three different stimulation paradigms, each with a different weighting of the grip force and its derivative, to explore the potential benefits of a more bioinspired stimulation strategy. In all paradigms, the participant's ability to identify the objects was above-chance, with object identification accuracy reaching 80% correct when using only sustained grip force feedback and 76.7% when using equal weighting of both sustained grip force and its derivative. These results demonstrate that bioinspired ICMS can provide sensory feedback that is functionally beneficial in sensorimotor tasks. Designing more efficient stimulation paradigms is important because it will allow us to 1) provide safer stimulation delivery methods that reduce overall injected charge without sacrificing function and 2) more effectively transmit sensory information to promote intuitive integration and usage by the human body.

Defining eloquent cortex intraoperatively, traditionally performed by neurosurgeons to preserve patient function, can now help target electrode implantation for restoring function. Brain-machine interfaces (BMIs) have the potential to restore upper-limb motor control to paralyzed patients but require accurate placement of recording and stimulating electrodes to enable functional control of a prosthetic limb. Beyond motor decoding from recording arrays, precise placement of stimulating electrodes in cortical areas associated with finger and fingertip sensations allows for the delivery of sensory feedback that could improve dexterous control of prosthetic hands. In this study, the authors demonstrated the use of a novel intraoperative online functional mapping (OFM) technique with high-density electrocorticography to localize finger representations in human primary somatosensory cortex. In conjunction with traditional pre- and intraoperative targeting approaches, this technique enabled accurate implantation of stimulating microelectrodes, which was confirmed by postimplantation intracortical stimulation of finger and fingertip sensations. This work demonstrates the utility of intraoperative OFM and will inform future studies of closed-loop BMIs in humans.

Introduction: Children with disorders of consciousness (DOC) represent the highest end of the acquired brain injury (ABI) severity spectrum for survivors and experience a multitude of functional impairments. Current clinical management in DOC uses behavioural evaluation measures and interventions that fail to (1) describe the physiological consequences of ABI and (2) elicit functional gains. In paediatric DOC, there is a critical need to develop evidence-based interventions to promote recovery of basic responses to improve rehabilitation and aid decision-making for medical teams and caregivers. The purpose of this investigation is to examine the safety, tolerability and feasibility of transcranial direct current stimulation (tDCS) in children with DOC., Methods and Analysis: This study is an open-label dose escalation trial evaluating the safety, tolerability and feasibility of tDCS in 10 children (5-17 years) receiving inpatient rehabilitation for DOC. This study will follow a modified rule-based design, allowing for intrapatient escalation, where a cohort of patients will be assigned to an initial tDCS current of 0.5 or 1 mA based on participant's head circumference and according to the safety data available in other paediatric populations. The subsequent assignment of increased current (1 or 2 mA) according to the prespecified rules will be based on the clinical observation of adverse events in the patients. The study will include up to three, 20 min sessions of anodal tDCS (sham, 0.5 or 1 mA, 1 or 2 mA) applied over the dorsolateral prefrontal cortex. The primary outcomes are adverse events, pain associated with tDCS and intolerable disruption of inpatient care. Secondary outcomes are changes in electroencephalography (EEG) phase-locking and event-related potential components and the Coma Recovery Scale-Revised total score from prestimulation to poststimulation., Ethics and Dissemination: The Johns Hopkins IRB (#IRB00174966) approved this study. Trial results will be disseminated through journals and conferences., Registration Number: NCT03618849., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To systematically examine the safety and effectiveness of transcranial direct current stimulation (tDCS) interventions in pediatric motor disorders., Data Sources: PubMed, EMBASE, Cochrane, CINAHL, Web of Science, and ProQuest databases were searched from inception to August 2018., Study Selection: tDCS randomized controlled trials (RCTs), observational studies, conference proceedings, and dissertations in pediatric motor disorders were included. Two authors independently screened articles based on predefined inclusion criteria., Data Extraction: Data related to participant demographics, intervention, and outcomes were extracted by 2 authors. Quality assessment was independently performed by 2 authors., Data Synthesis: A total of 23 studies involving a total of 391 participants were included. There was no difference in dropout rates between active (1 of 144) and sham (1 of 144) tDCS groups, risk difference 0.0, 95% confidence interval (-.05 to .04). Across studies, the most common adverse effects in the active group were tingling (17.2%), discomfort (8.02%), itching (6.79%), and skin redness (4%). Across 3 studies in children with cerebral palsy, tDCS significantly improved gait velocity (MD=.23; 95% confidence interval [0.13-0.34]; P<.0005), stride length (MD=0.10; 95% confidence interval [0.05-0.15]; P<.0005), and cadence (MD=15.7; 95% confidence interval [9.72-21.68]; P<.0005). Mixed effects were found on balance, upper extremity function, and overflow movements in dystonia., Conclusion: Based on the studies reviewed, tDCS is a safe technique in pediatric motor disorders and may improve some gait measures and involuntary movements. Research to date in pediatric motor disorders shows limited effectiveness in improving balance and upper extremity function. tDCS may serve as a potential adjunct to pediatric rehabilitation; to better understand if tDCS is beneficial for pediatric motor disorders, more well-designed RCTs are needed., (Copyright © 2018 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

Background: Transcranial magnetic stimulation (TMS) can be combined with functional magnetic resonance imaging (fMRI) to simultaneously manipulate and monitor human cortical responses. Although tremendous efforts have been directed at characterizing the impact of TMS on image acquisition, the influence of the scanner's static field on the TMS coil has received limited attention., Objective/hypothesis: The aim of this study was to characterize the influence of the scanner's static field on TMS. We hypothesized that spatial variations in the static field could account for TMS field variations in the scanner environment., Methods: Using an MRI-compatible TMS coil, we estimated TMS field strengths based on TMS-induced voltage changes measured in a search coil. We compared peak field strengths obtained with the TMS coil positioned at different locations (B0 field vs fringe field) and orientations in the static field. We also measured the scanner's static field to derive a field map to account for TMS field variations., Results: TMS field strength scaled depending on coil location and orientation with respect to the static field. Larger TMS field variations were observed in fringe field regions near the gantry as compared to regions inside the bore or further removed from the bore. The scanner's static field also exhibited the greatest spatial variations in fringe field regions near the gantry., Conclusions: The scanner's static field influences TMS fields and spatial variations in the static field correlate with TMS field variations. Coil orientation changes in the B0 field did not result in substantial TMS field variations. TMS field variations can be minimized by delivering TMS in the bore or outside of the 0-70 cm region from the bore entrance., (Copyright © 2014 Elsevier Inc. All rights reserved.)