Introduction

The Peripheral Neuropathy Solution

The Peripheral Neuropathy Program

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The possibility of interfacing the nervous system with electronic devices has long fascinated scientists, engineers and physicians. In general, an ability to expand the bandwidth of the communication between brain and machine would provide many interesting possibilities, ranging from faster human-computer interfaces to direct remote control (i.e., "telekinesis"). In medicine, the field of neuroprosthetics has grown rapidly to include a variety of devices for stimulating neural tissue. Chapters 1-5 of this volume outline the present usefulness and future promise of such devices in the central and the peripheral nervous systems and in muscle. One of the most interesting areas for further development of this field is the use of simultaneously recorded neurons in the brain to control robotic devices. Chapters 6-9 consider the possible scientific and clinical advantages of using implanted devices to record signals from the nervous system, and then employ them to restore neurological function. The combination of these two technologies could play a particularly important role in restoring lost motor function in paralysis patients. An injury to the spinal cord in the neck, for example, could interrupt the flow of "motor command" information from the brain to the arm and also the flow of sensory feedback from the arm to the brain.

As schematized in Figure 1, the emerging field of "neurorobotics" seeks to obtain motor command signals from motor control regions of the brain and transform them into electronic signals suitable for controlling a robotic device. The primary motor cortex (MI), in the precentral gyrus of the human cerebral cortex, has long been known to be important for the control of voluntary limb movements. It is therefore conceivable that one could record commands for arm movement in the MI cortex and use those signals to directly drive a robotic arm of similar configuration (see Chapters 7 and 8). We have recently demonstrated the feasibility of such neuroro-botic control in rats, and similar studies are ongoing in monkeys.

"Neuroprosthetics" (Figure 1) constitute another approach to the problem of restoring movement in paralyzed patients through functional electrical stimulation (FES; also called functional neuromuscular stimulation, FNS) of muscles or muscle nerves. For example, devices currently in use can produce grasping movements in a paralyzed hand through FES in the forearm musculature. These devices can be controlled through movement of other body areas, such as the unparalyzed contralateral shoulder.

Notwithstanding these futuristic scenarios, neural prostheses are rapidly becoming viable therapies for a broad range of patients with injury or disease of the nervous system. For example, over 3000 auditory prostheses have been successfully implanted in deaf patients (see Chapter 1) and over 150 devices for FES that restore grasping have been implanted in patients who have suffered loss of function in their upper extremities (see Chapters 2 and 3). This volume will present several different types of neural prosthetic devices as well as recent advances in cutting-edge research

FIGURE 1 "Neurorobotics" refers to the use of brain-derived activity to control a robotic device. In the hypothetical case illustrated here, arrays of recording electrodes surgically implanted in the motor cortex and adjoining areas could be used to extract motor information from the brain. An online computational device (here, a neural network) could be used to transform the multichannel neural information into output signals appropriate for controlling a human-like robot arm. "Neuroprosthetics" generally refers to the use of electrical stimulation to artificially restore function of neural or muscle tissue. Chapters 2 and 3 describe existing methods for functional neuromuscular stimulation (FNS) to activate paralyzed muscles. As illustrated here, one might utilize brain-derived signals to provide command signals for such an FNS system to control the musculature of a paralyzed arm. As in the neurorobotic paradigm, a realtime computational device would be needed to transform the multichannel brain signals into FNS output signals sufficient to activate several arm muscles and coordinate their movements. Beyond this, it will ultimately be desirable to obtain sensory feedback from nerves in the arm (see Chapter 5) and feed that sensory information back into the brain. This would provide "closed-loop" control of the prosthetic device, allowing the brain to control the arm with much greater accuracy.

for novel devices to restore sensory and motor function in patients with neural damage. These chapters are intended to review the techniques underlying recently developed neural prosthetics that stimulate nerves and muscles to restore sensory or motor function. This area has shown rapid growth in the past decade. The realm of neural prosthetic devices spans stimulation of peripheral nerves for the restoration of motor function (FES), stimulating electrodes for repair of sensory systems (i.e., auditory), as well as the emerging field of devices implanted directly into the brain to control these prosthetic devices.

This book is divided into two sections. The first section provides details about some of the most successful sensory and motor prosthetic devices available. The second section reveals recent research into using brain signals to control a neural prosthetic device or an external device to restore sensory or motor function. In the first section, Chapter 1 presents an overview of the highly successful auditory prosthetic devices. These devices are now routinely implanted in patients with nerve damage and are widely successful in restoring hearing. Chapters 2 through 5 explore different approaches to the use of functional electrical stimulation for the restoration of motor control. Chapters 2 and 3 present devices developed and used in clinical settings for restoration of motor function in patients with spinal cord injury or disease. Chapter 2 describes a device that has been used to restore grasping in spinal-cord-injured patients. Chapter 3 presents the BION™ implant that performs FES to maintain muscle tone in patients who have lost the use of their limbs through spinal cord injury or stroke and its use for stimulating muscles to restore grasp. In Chapter 4 the latest advances in direct stimulation of the spinal cord for restoration of locomotion are examined. This chapter focuses on using FES of the spinal cord to control the limb movements during locomotion. Chapter 5 presents a nerve cuff electrode to record and modulate neural activity.

The next three chapters, making up the second part of the book, explore the growing field of brain-implantable devices to control artificial prosthetic devices or neural prosthetics described in Part 1 of this book. Chapter 6 introduces the electrodes and hardware that are traditionally used to record brain signals and the issues involved with creating a device for clinical applications. Some of the inherent problems with devices implanted directly into the brain are also discussed. Chapter 7 presents a case study of a successful control device implanted into the cortex of a severe shut-in patient. The patient has successfully used this device to control a cursor on a computer screen. Chapter 8 presents recent research data showing feasibility of brain-controlled neurorobotic devices. Finally, Chapter 9 provides a new perspective on combining neurochemical and neurophysiological information to create prosthetic control devices that restore chemical balance to the brain.

We would like to take this opportunity to thank the editors of the CRC Methods in Neuroscience Series, Drs. Nicolelis and Simon, for giving us the opportunity to put this book together. Without their enthusiasm and continued support, this project could not have been completed. Finally, we would like to thank the many people at CRC Press for their constant support and especially Barbara Norwitz, CRC Life Sciences Publisher, for her critical support in bringing this project to print.

Department of Neurobiology State University of New York Health Science Center at Brooklyn Brooklyn, NY

School of Biomedical Engineering Science and Health Systems Drexel University Philadelphia, PA

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