Notes On Neuroprosthetics

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Pages: 38

Chapter 6
Arthur Prochazka, PhD

Chapter Objectives

Following this chapter the reader will be able to:
1. Understand the basic principles of operation of neuroprostheses (NPs).
2. Appreciate the historical development of NPs.
3. Assess the main benefits and limitations of existing NPs.
4. Recommend the type of NP that might benefit a particular person.
5. Evaluate new NP technologies as they evolve.

Chapter Outline

A. Definition.
B. History
A. Electrical stimulation of nerves
B. Therapeutic carry-over effects
A. Surface FES devices.
1. Surface stimulation devices for enhancing walking function.
2. Surface stimulation devices for enhancing hand function.
B. Implanted NPs.
1. General: cochlear, phrenic nerve, deep brain and sacral stimulators
2. Implanted devices for enhancing walking function
3. Intraspinal microstimulation
4. Implanted devices for enhancing hand function
5. Bladder Control
A. Level of injury
B. Time after injury
C. Risks and contraindications

Spinal Cord Injury Rehabilitation

Page 2

A. Definition.
Neuroprostheses (NPs) are electronic devices that stimulate nerves to improve bodily functions lost as a result of damage to the peripheral or central nervous system. This approach is also called functional electrical stimulation (FES) or functional neuromuscular stimulation (FNS). NPs include both surface stimulators that deliver current through the skin to target nerves and implanted stimulators that deliver current directly to the target nerves. On this definition, NPs range from simple “muscle” stimulators used to increase muscle bulk, to complex devices implanted in the spinal cord and brain. The aim of this chapter is to describe the numerous types of NPs that have been developed since the early days of therapeutic electrical stimulation (TES), with a particular emphasis on those NPs that are useful in functional restoration after spinal cord injury (SCI). The spectacular advances that have occurred in the neurosciences and in biomedical engineering in the last two decades have led to numerous technical advances and innovations. Surface and implanted
NPs are now available to assist with a wide variety of functions including hand function, postural control, standing, walking, respiration, micturition and pain control. This chapter will address issues related to the benefits and limitations of these devices and factors affecting the choice of an
NP for a particular individual.
B. History.
Electrostatic machines capable of generating single high-voltage pulses were invented in the 1740s.
Clinicians very soon began using them to apply single stimuli through pairs of surface electrodes, more to impress than to provide therapy 1, 2. Michael Faraday’s invention of the induction coil in the mid-19th century allowed continuous trains of stimuli to be delivered to nerves and muscles.
“Faradic” stimulation quickly became an important means of experimentally stimulating the brain, spinal cord and peripheral nerves (see Mechanisms below).
Advanced Concept Call-out
The amount of current required to activate muscle fibers is more than 10 times greater than that required to activate the nerve that innervates them, so muscle stimulators are really nerve stimulators. Denervated muscles cannot be activated with the pulse amplitudes normally used in
FES, so individuals with lesions that have destroyed the relevant motoneuron pools in the gray matter of the spinal cord, or the motoneuronal axons in spinal nerves (as occurs in cauda equina lesions), unfortunately often do not benefit from FES.
The first detailed manual of motor points, i.e. locations at which Faradic stimulation through the skin activated muscles at the lowest thresholds, was published in 1867 3.
Electrical stimulation continued to be used at the fringes of medicine until the 1960s, when the