Friday, December 15, 2006

The Promise and Perils of "Neural Prostheses"

Stories of researchers and patients that engage the reader in understanding the development of "neural prostheses," devices that interact directly with the brain or nervous system to enable the deaf to hear, the blind to see, and the paralyzed to move.

In Shattered Nerves, Victor D. Chase explores the development of “neural prostheses,” devices that interact directly with nerves or the brain to try to compensate for the lost functions of an injured nervous system. As he himself says, a comprehensive record of this field would require something more the size of an encyclopedia than the 289 pages he has produced. Instead, Chase furnishes an overview of the field, its technology, and the people in it. He achieves his formidable aim, enabling the reader to make connections between scientific endeavor and its application to the lives of the vivid individuals to whom he introduces us.

Any injury affecting the ability to use a limb has consequences beyond the purely physical. The injury, the reactions of other people, and the altered sense of self that patients experience can all have a profound impact. Generally, spinal injuries hinder not just the capacity to use limbs but also the ability to control bladder and bowel function and to have sex. These injuries, therefore, not only affect a person’s ability to carry out day-to-day tasks but may also make reliable control of continence impossible, leading to yet greater prejudice and social isolation. Similar problems plague those with injuries to other parts of the nervous system, such as vision and hearing.

Chase engages his readers by encouraging them to follow the patients’ and researchers’ learning process as they seek to develop and use neural prostheses. By revealing what the science means to a specific person—a quadriplegic woman who becomes able to walk down the aisle at her wedding, for instance—he makes the scientific knowledge accessible and gives resonance to its significance.

Both the general subject matter and the individual stories could have made for a long, sad read, but Chase uses the stories well, showing the huge amounts of determination that people are able to generate to overcome their injuries and also the benevolence and fortitude that they are capable of displaying by acting as experimental subjects. 

From Electricity to Ethics

Most human tissues have some ability to re-grow after injury or surgery. The brain, spine, eyes, and ears generally do not. Injuries to these organs are permanent, creating particular problems for the surgeons and physicians who treat injuries, tumors, or other disorders affecting the nervous system. Scientists now know that nerve cells can regenerate in certain circumstances, and considerable research effort is devoted to this field. So far, however, no major surgical or pharmacological solutions are available for day-to-day clinical use, hence the need for neural prostheses.

I have often felt that the rapid increase in the complexity and capability of consumer electronic devices, as well as their continuing miniaturization, should offer hope for medical applications. If mass-market cameras are now sophisticated enough to focus on individual faces, produce images that can be printed at poster size, and still fit in the palm of one’s hand, we might speculate that an eyeball-size camera is not far away. Chase describes the advances that this technological sophistication has allowed and the problems that remain to be conquered. He starts by explaining how nerve and muscle cells use electricity to function and outlining the basic organization of the central and peripheral nervous systems. This discussion provides the basis for later parts of the book, in which he describes research of the eighteenth, nineteenth, and twentieth centuries, including experiments in how to generate electricity in the first place and some of the first experiments on the nervous system, such as the results of placing an electrode in one’s ear.

Chase then takes us through the problems of designing, coordinating, controlling, and powering neural prostheses, as well as the postoperative tuning necessary to enable an exceedingly complex brain to derive maximum benefit from a device with a very limited number of input channels. He describes the experiments that help researchers determine the physiological rules governing neuronal and muscular stimulation and also the technology necessary to develop devices that can reliably stimulate nerves and last many years in the body without producing toxicity. He explains the chemical challenges involved in selecting the correct materials for making electrodes and the engineering challenges in manufacturing these electrodes at microscopic sizes. Finally, he delves into the ethics of neural implantation, such as whether we should implant prostheses in non-injured humans in an attempt to augment their function. 

Seeking Hope and Healing

Chase provides a very thorough overview of this field, from A.D. 50 to the present day and from prostheses designed to help hearing, to those that enable people to use paralyzed hands and receive enough feedback to control them. He provides insights into the lives of patients who need implants and the emotional and physical upheavals they go through, as well as showing very clearly the successes that research has had to date and the profound challenges that remain. Most important, by focusing on the stories of a colorful cast of patients and researchers, he makes Shattered Nerves easy and entertaining to read. Chase’s powers of description and his insights into character are put to good use throughout the book, and he clearly has a great deal of admiration for the individuals he portrays. In a society that too often defines people by their injuries, Chase’s patients speak for themselves and come to define themselves instead by their aspirations.

The case studies in Shattered Nerves illustrate how relatively small improvements (for example, to perceive a few dots of light or channels of sound) may not only produce surprising increases in a patient’s ability to function physically but also have dramatic psychological benefits. One patient explains how his partial and then complete loss of hearing forced him to reevaluate the nature of remedy: “Our concept of healing and recovery often takes on new meaning, one that is focused on the spiritual and psychological, rather than a physical recovery. If we can no longer expect to join nerves back together, we can instead try to reconfigure the soul and the self.” In this context, the reader can understand the disproportionate feelings of emotional well-being experienced by patients who make seemingly modest gains.

One of the problems facing researchers and clinicians involved in treating injuries to the brain and nervous system is that both patients and their relatives are understandably keen to seize upon any chance of improvement. Hope and the determination to overcome problems are vital attributes for both patients and researchers, but this technology is still in its infancy and false hopes can be damaging. One of the many strengths of Shattered Nerves is that through the author’s description of the numerous difficulties that have been overcome in reaching the current level of implant sophistication, readers gain a clear understanding of the difficulties that must yet be overcome in order to make further advances. 

A Broadly Appealing Story

Perhaps when Chase introduces us to “the grandfather of neural prostheses,” Giles Brindley, and tells the hilarious and slightly disturbing story of this “grandfather” dropping his trousers in front of a lecture theater audience, one should be grateful that there are no illustrations in the book. Chase rarely uses scientific jargon and explains it well when he does. He is very good at describing the prostheses and procedures, and the absence of illustrations is more than compensated for by the amount of information that he covers and his clear writing style. On balance, however, the book would benefit from diagrams of the parts of the nervous system affected by various conditions and photographs or illustrations of the prostheses and surgical procedures described. 

One of Chase’s most notable achievements in Shattered Nerves is that he has written about his narrow, specialized subject matter with such broad appeal. The reader already familiar with this field is still likely to end up better informed and certainly entertained by Chase’s character sketches, while readers from a non-neuroscience background will find an extremely thorough and balanced introduction to neural prostheses, presented in an enjoyable and accessible way.  Irrespective of one’s profession or background, Chase’s approach to his patients and to his subject must surely inspire greater endeavor in us all.



About Cerebrum

Bill Glovin, editor
Carolyn Asbury, Ph.D., consultant

Scientific Advisory Board
Joseph T. Coyle, M.D., Harvard Medical School
Kay Redfield Jamison, Ph.D., The Johns Hopkins University School of Medicine
Pierre J. Magistretti, M.D., Ph.D., University of Lausanne Medical School and Hospital
Robert Malenka, M.D., Ph.D., Stanford University School of Medicine
Bruce S. McEwen, Ph.D., The Rockefeller University
Donald Price, M.D., The Johns Hopkins University School of Medicine

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