Interfacing with the nervous system: a review of current bioelectric technologies.

The aim of this study is to discuss the state of the art with regard to established or promising bioelectric therapies meant to alter or control neurologic function. We present recent reports on bioelectric technologies that interface with the nervous system at three potential sites-(1) the end organ, (2) the peripheral nervous system, and (3) the central nervous system-while exploring practical and clinical considerations. A literature search was executed on PubMed, IEEE, and Web of Science databases. A review of the current literature was conducted to examine functional and histomorphological effects of neuroprosthetic interfaces with a focus on end-organ, peripheral, and central nervous system interfaces. Innovations in bioelectric technologies are providing increasing selectivity in stimulating distinct nerve fiber populations in order to activate discrete muscles. Significant advances in electrode array design focus on increasing selectivity, stability, and functionality of implantable neuroprosthetics. The application of neuroprosthetics to paretic nerves or even directly stimulating or recording from the central nervous system holds great potential in advancing the field of nerve and tissue bioelectric engineering and contributing to clinical care. Although current physiotherapeutic and surgical treatments seek to restore function, structure, or comfort, they bear significant limitations in enabling cosmetic or functional recovery. Instead, the introduction of bioelectric technology may play a role in the restoration of function in patients with neurologic deficits.

Selective recurrent laryngeal nerve stimulation using a penetrating electrode array in the feline model.

OBJECTIVES/HYPOTHESIS: Laryngeal muscles (LMs) are controlled by the recurrent laryngeal nerve (RLN), injury of which can result in vocal fold (VF) paralysis (VFP). We aimed to introduce a bioelectric approach to selective stimulation of LMs and graded muscle contraction responses. STUDY DESIGN: Acute experiments in cats. METHODS: The study included six anesthetized cats. In four cats, a multichannel penetrating microelectrode array (MEA) was placed into an uninjured RLN. For RLN injury experiments, one cat received a standardized hemostat-crush injury, and one cat received a transection-reapproximation injury 4 months prior to testing. In each experiment, three LMs (thyroarytenoid, posterior cricoarytenoid, and cricothyroid muscles) were monitored with an electromyographic (EMG) nerve integrity monitoring system. Electrical current pulses were delivered to each stimulating channel individually. Elicited EMG voltage outputs were recorded for each muscle. Direct videolaryngoscopy was performed for visualization of VF movement. RESULTS: Stimulation through individual channels led to selective activation of restricted nerve populations, resulting in selective contraction of individual LMs. Increasing current levels resulted in rising EMG voltage responses. Typically, activation of individual muscles was successfully achieved via single placement of the MEA by selection of appropriate stimulation channels. VF abduction was predominantly observed on videolaryngoscopy. Nerve histology confirmed injury in cases of RLN crush and transection experiments. CONCLUSIONS: We demonstrated the ability of a penetrating MEA to selectively stimulate restricted fiber populations within the feline RLN and selectively elicit contractions of discrete LMs in both acute and injury-model experiments, suggesting a potential role for intraneural MEA implantation in VFP management. LEVEL OF EVIDENCE: NA. Laryngoscope, 128:1606-1614, 2018.

Selective Stimulation of Facial Muscles Following Chronic Intraneural Electrode Array Implantation and Facial Nerve Injury in the Feline Model.

BACKGROUND: Our group has previously shown that activation of specific facial nerve (FN) fiber populations and selective activation of facial musculature can be achieved through acute intraneural multichannel microelectrode array (MEA) implantation in the feline model. HYPOTHESIS: Selective stimulation of facial muscles will be maintained in the setting of 1) chronic and 2) acute MEA implantation after FN injury and subsequent recovery. METHODS: This study included seven cats. In three cats with normal facial function, 4-channel penetrating MEAs were implanted chronically in the FN and tested biweekly for 6 months. Electrical current pulses were delivered to each channel individually, and elicited electromyographic (EMG) voltage outputs were recorded for each of several facial muscles. For FN injury experiments, two cats received a standardized hemostat-crush injury, and two cats received a transection-reapproximation injury to the FN main trunk. These four underwent acute implantation of MEA and EMG recording in terminal experiments 4 months postinjury. RESULTS: Stimulation through individual channels selectively activated restricted nerve populations, resulting in activation of individual muscles in cats with chronic MEA implantation and after nerve injury. Increasing stimulation current levels resulted in increasing EMG voltage responses in all patients. Nerve histology showed only minor neural tissue reaction to the implant. CONCLUSION: We have established in the animal model the ability of a chronically implanted MEA to selectively stimulate restricted FN fiber populations and elicit activations in specific facial muscles. Likewise, after FN injury, selective stimulation of restricted FN fiber populations and subsequent activation of discrete facial muscles can be achieved after acute MEA implantation.