First-in-human demonstration of floating EMG sensors and stimulators wirelessly powered and operated by volume conduction

BACKGROUND

Recently we reported the design and evaluation of floating semi-implantable devices that receive power from and bidirectionally communicate with an external system using coupling by volume conduction. The approach, of which the semi-implantable devices are proof-of-concept prototypes, may overcome some limitations presented by existing neuroprostheses, especially those related to implant size and deployment, as the implants avoid bulky components and can be developed as threadlike devices. Here, it is reported the first-in-human acute demonstration of these devices for electromyography (EMG) sensing and electrical stimulation.

METHODS

A proof-of-concept device, consisting of implantable thin-film electrodes and a nonimplantable miniature electronic circuit connected to them, was deployed in the upper or lower limb of six healthy participants. Two external electrodes were strapped around the limb and were connected to the external system which delivered high frequency current bursts. Within these bursts, 13 commands were modulated to communicate with the implant.

RESULTS

Four devices were deployed in the biceps brachii and the gastrocnemius medialis muscles, and the external system was able to power and communicate with them. Limitations regarding insertion and communication speed are reported. Sensing and stimulation parameters were configured from the external system. In one participant, electrical stimulation and EMG acquisition assays were performed, demonstrating the feasibility of the approach to power and communicate with the floating device.

CONCLUSIONS

This is the first-in-human demonstration of EMG sensors and electrical stimulators powered and operated by volume conduction. These proof-of-concept devices can be miniaturized using current microelectronic technologies, enabling fully implantable networked neuroprosthetics.

Efficacy of functional electrical stimulation in rehabilitating patients with foot drop symptoms after stroke and its correlation with somatosensory evoked potentials-a crossover randomised controlled trial

OBJECTIVE

The connectivity between somatosensory evoked potentials (SEPs) and cortical plasticity remains elusive due to a lack of supporting data. This study investigates changes in pathological latencies and amplitudes of SEPs caused by an acute stroke after 2 weeks of rehabilitation with functional electrical stimulation (FES). Furthermore, changes in SEPs and the efficacy of FES against foot drop (FD) stroke symptoms were correlated using the 10-m walk test and foot-ankle strength.

METHODS

A randomised controlled two-period crossover design plus a control group (group C) was designed. Group A (n = 16) was directly treated with FES, while group B (n = 16) was treated after 2 weeks. The untreated control group of 20 healthy adults underwent repeated SEP measurements for evaluation only.

RESULTS

The repeated-measures ANOVA showed a decrease in tibial nerve (TN) P40 and N50 latencies in group A after the intervention, followed by a decline in non-paretic TN SEP in latency N50 (p < 0.05). Moreover, compared to groups B and C from baseline to 4 weeks, group A showed a decrease in paretic TN latency P40 and N50 (p < 0.05). An increase in FD strength and a reduction in step cadence in group B (p < 0.05) and a positive tendency in FD strength (p = 0.12) and step cadence (p = 0.08) in group A were observed after the treatment time. The data showed a moderate (r = 0.50-0.70) correlation between non-paretic TN latency N50 and step cadence in groups A and B after the intervention time.

CONCLUSION

The FES intervention modified the pathological gait in association with improved SEP afferent feedback. Registered on 25 February 2021 on ClinicalTrials.gov under identifier number: NCT04767360.

Harnessing the Power of Artificial Intelligence in Otolaryngology and the Communication Sciences

Use of artificial intelligence (AI) is a burgeoning field in otolaryngology and the communication sciences. A virtual symposium on the topic was convened from Duke University on October 26, 2020, and was attended by more than 170 participants worldwide. This review presents summaries of all but one of the talks presented during the symposium; recordings of all the talks, along with the discussions for the talks, are available at https://www.youtube.com/watch?v=ktfewrXvEFg and https://www.youtube.com/watch?v=-gQ5qX2v3rg . Each of the summaries is about 2500 words in length and each summary includes two figures. This level of detail far exceeds the brief summaries presented in traditional reviews and thus provides a more-informed glimpse into the power and diversity of current AI applications in otolaryngology and the communication sciences and how to harness that power for future applications.

Discriminability of multiple cutaneous and proprioceptive hand percepts evoked by intraneural stimulation with Utah slanted electrode arrays in human amputees

BACKGROUND

Electrical stimulation of residual afferent nerve fibers can evoke sensations from a missing limb after amputation, and bionic arms endowed with artificial sensory feedback have been shown to confer functional and psychological benefits. Here we explore the extent to which artificial sensations can be discriminated based on location, quality, and intensity.

METHODS

We implanted Utah Slanted Electrode Arrays (USEAs) in the arm nerves of three transradial amputees and delivered electrical stimulation via different electrodes and frequencies to produce sensations on the missing hand with various locations, qualities, and intensities. Participants performed blind discrimination trials to discriminate among these artificial sensations.

RESULTS

Participants successfully discriminated cutaneous and proprioceptive sensations ranging in location, quality and intensity. Performance was significantly greater than chance for all discrimination tasks, including discrimination among up to ten different cutaneous location-intensity combinations (15/30 successes, p < 0.0001) and seven different proprioceptive location-intensity combinations (21/40 successes, p < 0.0001). Variations in the site of stimulation within the nerve, via electrode selection, enabled discrimination among up to five locations and qualities (35/35 successes, p < 0.0001). Variations in the stimulation frequency enabled discrimination among four different intensities at the same location (13/20 successes, p < 0.0005). One participant also discriminated among individual stimulation of two different USEA electrodes, simultaneous stimulation on both electrodes, and interleaved stimulation on both electrodes (20/24 successes, p < 0.0001).

CONCLUSION

Electrode location, stimulation frequency, and stimulation pattern can be modulated to evoke functionally discriminable sensations with a range of locations, qualities, and intensities. This rich source of artificial sensory feedback may enhance functional performance and embodiment of bionic arms endowed with a sense of touch.

Brain-Machine Interfaces: The Role of the Neurosurgeon

Neurotechnology is set to expand rapidly in the coming years as technological innovations in hardware and software are translated to the clinical setting. Given our unique access to patients with neurologic disorders, expertise with which to guide appropriate treatments, and technical skills to implant brain-machine interfaces (BMIs), neurosurgeons have a key role to play in the progress of this field. We outline the current state and key challenges in this rapidly advancing field, including implant technology, implant recipients, implantation methodology, implant function, and ethical, regulatory, and economic considerations. Our key message is to encourage the neurosurgical community to proactively engage in collaborating with other health care professionals, engineers, scientists, ethicists, and regulators in tackling these issues. By doing so, we will equip ourselves with the skills and expertise to drive the field forward and avoid being mere technicians in an industry driven by those around us.

Intraneural electrical stimulation of median nerve: a simulation study on sensory and motor fascicles

Neuroprostheses can be an innovative solution to improve quality of life of upper limb amputees. In this framework, the recovery of sensory feedback is a property widely requested by amputee subjects. Neural prostheses are based on neural interfaces that allow delivering direct current stimuli to the nerve fibers. The study of the interaction between the nerve and the electrode is fundamental to investigate activation properties in the nerve. Furthermore, the results could provide useful insight into improve the design of the electrodes and to advance and ameliorate tactile sensations, elicited by these interfaces, obtaining tactile feedback more like natural sensations. This work aims at studying, by means of a FEM Neuron computational model, the axon fibers activation by means of neural stimulation provided through the intraneural electrodes DS-file. Three different types of stimulation waveforms (i.e. biphasic charge balanced stimulus with inter-pulse delay, biphasic charge balanced stimulus without inter-pulse delay, biphasic charge unbalanced stimulus with inter-pulse delay), three different nerve fascicles, i.e. two sensory and one motor fascicle, and ten distances from the electrode in the fascicles, are considered. The efficacy of the stimulation expressed as the percentage of activation of the fibers, and the safety, in terms of current intensity and used waveform, are studied in the previously described different conditions and the results are compared. The obtained results show that: i. stimulating a sensory fascicle with implanted active sites can activate a fascicle close to it, but not all the fascicles belonging to the same nerve. In fact, in the nerve considered in this study, a motor fascicle cannot be activated due to the values of the electrical potential which are too low to activate the fibers; ii. the current intensity necessary to activate fibers increases according to the distance from the source of the stimulus; iii. by using a biphasic charge unbalanced stimulus, the threshold to activate the fibers is lower than using the other tested waveforms. It is an important result because the stimulation is efficient and safer since current intensity is lower than the one used for the other two waveforms.

Sum of phase-shifted sinusoids stimulation prolongs paralyzed muscle output

Neuroprostheses that activate musculature of the lower extremities can enable standing and movement after paralysis. Current systems are functionally limited by rapid muscle fatigue induced by conventional, non-varying stimulus waveforms. Previous work has shown that sum of phase-shifted sinusoids (SOPS) stimulation, which selectively modulates activation of individual motor unit pools (MUPs) to lower the duty cycle of each while maintaining a high net muscle output, improves joint moment maintenance but introduces greater instability over conventional stimulation. In this case study, implementation of SOPS stimulation with a real-time feedback controller successfully decreased joint moment instability and further prolonged joint moment output with increased stimulation efficiency over open-loop approaches in one participant with spinal cord injury. These findings demonstrate the potential for closed-loop SOPS to improve functionality of neuroprosthetic systems.

Spatiotemporal characteristics of neural activity in tibial nerves with carbon nanotube yarn electrodes

BACKGROUND

Reliable interfacing with peripheral nervous system is essential to extract neural signals. Current implantable peripheral nerve electrodes cannot provide long-term reliable interfaces due to their mechanical mismatch with host nerves. Carbon nanotube (CNT) yarns possess excellent mechanical flexibility and electrical conductivity. It is of great necessity to investigate the selectivity of implantable CNT yarn electrodes.

NEW METHOD

Neural interfaces were fabricated with CNT yarn electrodes insulated with Parylene-C. Acute recordings were carried out on tibial nerves of rats, and compound nerve action potentials (CNAPs) were electrically evoked by biphasic current stimulation of four toes. Spatiotemporal characteristics of neural activity and spatial selectivity of the electrodes, denoted by selectivity index (SI), were analyzed in detail.

RESULTS

Conduction velocities of sensory afferent fibers recorded by CNT yarn electrodes varied between 4.25 m/s and 37.56 m/s. The SI maxima for specific toes were between 0.55 and 0.99 across seven electrodes. SIs for different CNT yarn electrodes are significantly different among varied toes.

COMPARISON WITH EXISTING METHODS

Most single CNT yarn electrode with a ∼ 500 μm exposed length can be sensitive to one or two specific toes in rodent animals. While, it is only possible to discriminate two non-adjacent toes by multisite TIME electrodes.

CONCLUSION

Single CNT yarn electrode exposed ∼ 500 μm showed SI values for different toes comparable to a multisite TIME electrode, and had high spatial selectivity for one or two specific toes. The electrodes with cross section exposed could intend to be more sensitive to one specific toe.

Future of Neural Interfaces

The technological ability to capture electrophysiological activity of populations of cortical neurons through chronic implantable devices has led to significant advancements in the field of brain-computer interfaces. Recent progress in the field has been driven by developments in integrated microelectronics, wireless communications, materials science, and computational neuroscience. Here, we review major device development landmarks in the arena of neural interfaces from FDA-approved clinical systems to prototype head-mounted and fully implantable wireless systems for multi-channel neural recording. Additionally, we provide an outlook toward next-generation, highly miniaturized technologies for minimally invasive, vastly parallel neural interfaces for naturalistic, closed-loop neuroprostheses.

On the design of EEG-based movement decoders for completely paralyzed stroke patients

Background

Brain machine interface (BMI) technology has demonstrated its efficacy for rehabilitation of paralyzed chronic stroke patients. The critical component in BMI-training consists of the associative connection (contingency) between the intention and the feedback provided. However, the relationship between the BMI design and its performance in stroke patients is still an open question.

Methods

In this study we compare different methodologies to design a BMI for rehabilitation and evaluate their effects on movement intention decoding performance. We analyze the data of 37 chronic stroke patients who underwent 4 weeks of BMI intervention with different types of association between their brain activity and the proprioceptive feedback. We simulate the pseudo-online performance that a BMI would have under different conditions, varying: (1) the cortical source of activity (i.e., ipsilesional, contralesional, bihemispheric), (2) the type of spatial filter applied, (3) the EEG frequency band, (4) the type of classifier; and also evaluated the use of residual EMG activity to decode the movement intentions.

Results

We observed a significant influence of the different BMI designs on the obtained performances. Our results revealed that using bihemispheric beta activity with a common average reference and an adaptive support vector machine led to the best classification results. Furthermore, the decoding results based on brain activity were significantly higher than those based on muscle activity.

Conclusions

This paper underscores the relevance of the different parameters used to decode movement, using EEG in severely paralyzed stroke patients. We demonstrated significant differences in performance for the different designs, which supports further research that should elucidate if those approaches leading to higher accuracies also induce higher motor recovery in paralyzed stroke patients.

Reactive stepping with functional neuromuscular stimulation in response to forward-directed perturbations

Background

Implanted motor system neuroprostheses can be effective at increasing personal mobility of persons paralyzed by spinal cord injuries. However, currently available neural stimulation systems for standing employ patterns of constant activation and are unreactive to changing postural demands.

Methods

In this work, we developed a closed-loop controller for detecting forward-directed body disturbances and initiating a stabilizing step in a person with spinal cord injury. Forward-directed pulls at the waist were detected with three body-mounted triaxial accelerometers. A finite state machine was designed and tested to trigger a postural response and apply stimulation to appropriate muscles so as to produce a protective step when the simplified jerk signal exceeded predetermined thresholds.

Results

The controller effectively initiated steps for all perturbations with magnitude between 10 and 17.5 s body weight, and initiated a postural response with occasional steps at 5% body weight. For perturbations at 15 and 17.5% body weight, the dynamic responses of the subject exhibited very similar component time periods when compared with able-bodied subjects undergoing similar postural perturbations. Additionally, the reactive step occurred faster for stronger perturbations than for weaker ones (p < .005, unequal varience t-test.)

Conclusions

This research marks progress towards a controller which can improve the safety and independence of persons with spinal cord injury using implanted neuroprostheses for standing.

Pain in an era of armed conflicts: Prevention and treatment for warfighters and civilian casualties

Chronic pain is a common squealae of military- and terror-related injuries. While its pathophysiology has not yet been fully elucidated, it may be potentially related to premorbid neuropsychobiological status, as well as to the type of injury and to the neural alterations that it may evoke. Accordingly, optimized approaches for wounded individuals should integrate primary, secondary and tertiary prevention in the form of thorough evaluation of risk factors along with specific interventions to contravene and mitigate the ensuing chronicity. Thus, Premorbid Events phase may encompass assessments of psychological and neurobiological vulnerability factors in conjunction with fostering preparedness and resilience in both military and civilian populations at risk. Injuries per se phase calls for immediate treatment of acute pain in the field by pharmacological agents that spare and even enhance coping and adaptive capabilities. The key objective of the Post Injury Events is to prevent and/or reverse maladaptive peripheral- and central neural system's processes that mediate transformation of acute to chronic pain and to incorporate timely interventions for concomitant mental health problems including post-traumatic stress disorder and addiction We suggest that the proposed continuum of care may avert more disability and suffering than the currently employed less integrated strategies. While the requirements of the armed forces present a pressing need for this integrated continuum and a framework in which it can be most readily implemented, this approach may be also instrumental for the care of civilian casualties.

Retinal prostheses: clinical results and future challenges

Retinal prostheses aim at restoring visual perception in blind patients affected by retinal diseases leading to the loss of photoreceptors, such as age-related macular degeneration or retinitis pigmentosa. Recent clinical trials have demonstrated the feasibility of this approach for restoring useful vision. Despite a limited number of electrodes (60), and therefore of pixels, some patients were able to read words and to recognize high-contrast objects. Face recognition and independent locomotion in unknown urban environments imply technological breakthroughs to increase the number and density of electrodes. This review presents recent clinical results and discusses future solutions to answer the major technological challenges.