A peripheral nerve interface is the bridge between the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

and a computer interface which serves as a bi‐directional information

transducer A transducer is a device that Energy transformation, converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, M ...

recording and sending signals between the human body and a machine processor. Interfaces to the nervous system usually take the form of electrodes for stimulation and recording, though chemical stimulation and sensing are possible. Research in this area is focused on developing peripheral nerve interfaces for the restoration of function following disease or injury to minimize associated losses. Peripheral nerve interfaces also enable electrical stimulation and recording of the peripheral nervous system to study the form and function of the peripheral nervous system. For example, recent animal studies have demonstrated high accuracy in tracking physiological meaningful measures, like joint angle. Many researchers also focus in the area of neuroprosthesis, linking the human nervous system to

bionics Bionics or biologically inspired engineering is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology. The word ''bionic'', coined by Jack E. Steele in August 195 ...

in order to mimic natural sensorimotor control and function. Successful implantation of peripheral nerve interfaces depend on a number of factors which include appropriate indication, perioperative testing, differentiated planning, and functional training. Typically microelectrode devices are implanted adjacent to, around or within the nerve trunk to establish contact with the peripheral nervous system. Different approaches may be used depending on the type of signal desired and attainable.

Function

The primary purpose of a neural interface is to enable two-way exchange of information with the nervous system for a sustained period of time to enable effective and high density stimulation and recording. The peripheral nervous system (PNS) is responsible for relaying information from the brain and spinal cord to the extremities of the body and back. The function of a peripheral nerve interface is to assist the nervous system when peripheral nerve function is compromised. To supplement the roles of the nervous system, interfaces need to augment motor function as well as discern sensory information. The feasibility of peripheral nerve stimulation to achieve a desired motor output has been demonstrated and is one of the major driving forces for this area of research. Information throughout the nervous system is exchanged primarily through

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

s. These signals occur at varying numbers and intervals dependent on both the

neuroanatomical Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defin ...

and

neurochemical A neurochemical is a small organic molecule or peptide that participates in neural activity. The science of neurochemistry studies the functions of neurochemicals. Prominent neurochemicals Neurotransmitters and neuromodulators *Glutamate is th ...

make up of the individual and localized region. Information may be either introduced or read out by inducing or recovering action potentials from the body. Successful development and implementation of a peripheral nerve interface would allow for both the introduction of information to the nervous system, and extraction of information from the nervous system.

Problems and limitations

Problems and limitations in peripheral nerve interfacing are both biophysical and biological in nature. These challenges include: *Fidelity of the interface in terms of functional resolution *Relatively weak, noise-ridden electrical signals causing a challenging interface design constraint *Interface implantation-associated injury to nerve fibers of interest *Stability of the interface over time due to inflammation *Managing inadvertent consequences such as pain or false sensory/motor stimulation due to physical movement or inflammation-associated triggering of neural activity

Application

Peripheral nerve interfaces are used for pain modulation, restoration of motor function following

spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Symptoms of ...

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

, treatment of epilepsy by electrical stimulation of the vagus nerve,

nerve stimulation Neuromodulation is "the alteration of nerve activity through targeted delivery of a stimulus, such as electrical stimulation or chemical agents, to specific neurological sites in the body". It is carried out to normalize – or modulate – ...

to control micturition, occipital nerve stimulation for chronic migraines and to interface with

neuroprosthetics Neuroprosthetics (also called neural prosthetics) is a discipline related to neuroscience and biomedical engineering concerned with developing neural prostheses. They are sometimes contrasted with a brain–computer interface, which connects the ...

Types

A wide variety of electrode designs have been researched, tested, and manufactured. These electrodes lie on a spectrum varying in degrees of invasiveness. Research in this area seeks to address issues centered around peripheral nerve/tissue damage, access to efferent and afferent signals, and selective recording/stimulation of nerve tissue. Ideally peripheral nerve interfaces are optimally designed to interface with biological constraints of peripheral nerve fibers, match the

mechanical Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations o ...

and electrical properties of the surrounding tissue, biocompatible with minimal immune response, high

sensor resolution A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

, are minimally invasive, and chronically stable with low

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

s. Strongest signals are recorded from

nodes of ranvier Nodes of Ranvier ( ), also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated axonal domains that are high in sodium and potassium ion channels ...

. Peripheral nerve interfaces may be divided into extraneural and intrafascular categories.

Epineurial electrode interface

Epineurial electrodes are fabricated as longitudinal strips holding two or more contact sites to interface with peripheral nerves. These electrodes are placed on the nerve and secured by suturing to the epineurium. The suturing process requires delicate surgery and can be torn from the nerve if excessive motion creates tension. Since the electrode is sutured to the epineurium it is unlikely to damage the nerve trunk.

Helicoidal electrode interface

Helicoidal electrodes are placed circumjacent to the nerve and are made of flexible platinum ribbon in a helical design. This design allows the electrode to conform to the size and shape of the nerve in attempts to minimize mechanical trauma. The structural design causes low selectivity. Helicoidal electrodes are currently used for FES stimulation of the

vagus nerve The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

to control intractable

epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

sleep apnea Sleep apnea (sleep apnoea or sleep apnœa in British English) is a sleep-related breathing disorder in which repetitive Apnea, pauses in breathing, periods of shallow breathing, or collapse of the upper airway during sleep results in poor vent ...

, and to treat depressive syndromes.

Book electrode interface

The book electrode consists of a silicone rubber block with slots. Each slot contains three platinum foils which function as electrodes, anode electrodes and one cathode. The spinal roots of the nerve are placed into these slots and the slots are then covered with a flap made of silicone and fixed with silicone glue. This electrode is mostly used to interrupt reflex circuits of the dorsal sacral roots and to control bladder function. Book electrodes are still considered very bulky.

References

{{reflist DARPA projects Human–computer interaction Implants (medicine) Neural engineering Neuroprosthetics User interface techniques Virtual reality