More has been learned about the workings of the brain and nervous system in the last fifty years than in all of preceding history. Rapid accumulation of data and the generation of new understanding and insights into the workings of the brain and nervous system continues. As we proceed into the 21st Century, the enormously ambitious and difficult goal of neuroscience, to understand how the brain and nervous system function to mediate behavior (including the mental and emotional life of humans), seems much closer. The explosive growth of neuroscience, brought about in large part through the development of powerful new tools of investigation, makes realistic the expectation that the next few decades will see the answer to many of the major questions that have bedevilled philosophers throughout the centuries and intrigued neuroscientists since the relatively recent emergence of this field. We are now able to solve problems and answer questions about the brain and the mind that only a few years ago were not even approachable. Many new tools and techniques have powered the rapid development of our knowledge of the brain: Neuroimaging - from light microscopy and electron microscopy to the startling new revelations of functional imaging of the brain in action. Neurophysiology - from electroencephalography and evoked potentials to the newly developing capabilities of biophysical and magnetic measurement of brain and brain cell activity. Neuroembryology and development - from chemical and observational tracing and computerized reconstruction of growth to molecular genetic methods of understanding neurobiological developmental processes, which may also shed some light on the mysteries of learning and memory. The momentum of these exciting new developments will carry us well into the new century. Perhaps a more complete understanding of the basis of brain and behavior will soon be within our grasp. This continuing explosive growth has produced a proliferation of information so great that it is almost impossible for scientists and practitioners in the field, using traditional methods, to keep up to date and remain knowledgeable about their own specialties in the field, much less to be aware of developments in the field as a whole. The Encyclopedia of Neuroscience is intended to help sort out, codify, and bring together key information from this overwhelming mass of neuroscience information. By making information available in the context of its relevance to subject categories, and thus more readily retrievable, we hope that the Encyclopedia will contribute to this dramatic research progress. We hope it will also encourage wider interest in, and support for, this most intriguing of all scientific questions: How does the brain, the organ of mind, understand itself? The First Edition of the Encyclopedia of Neuroscience, published 15 short years ago, was intended to help relieve the information glut, which was becoming serious even at that time. The first general encyclopedia for the field, it made accessible in two volumes and 700 short articles the whole range of information on the neurosciences. But even with three supplemental volumes, it could not keep pace with the developments in the field. With recognition of this, it was decided to take advantage of rapidly evolving electronics and computer technology and produce a new edition of the Encyclopedia as a CD-ROM electronic "publication", readily revisable and updatable, complete with full electronic search engines and an array of interactive videos and animations. The Encyclopedia would also provide selected direct access to a world of additional information through the Internet. And so the Second Edition of the Encyclopedia of Neuroscience was published in 1998 on CD-ROM, and a year later in a two-volume print edition. But, the enormously rapid growth of discovery and new findings in neuroscience persuaded us that the field needed a new and updated version of the Encyclopedia, one that would more fully cover the spectacular new developments in neuroscience, basic and clinical, and take full advantage of the latest techniques of electronic data presentation. So here is the Third Edition, five years after the Second, featuring broader coverage of the field through an increased number of somewhat longer entries, and presented in the form of CD-ROM with outward linking to the Web, which combines the flexibility and ease of use of the CD-ROM with the world-wide coverage of the Internet, enabling the reader who needs more information on a topic to access it directly in the cited literature. Thus, the Encyclopedia makes accessible in an organized and systematic way, the whole world of neuroscience, research and applications, a veritable library of neuroscience information in "compact" form. It remains an authoritative source of information for all areas of neuroscience, basic as well as clinical. Consisting in more than 900 alphabetically arranged articles, each written by one or more experts, plus animations, videos, and other illustrations, this CD-ROM version makes data and information more readily accessible through search and browse functionality. Through video clips and specially prepared animations illustrating brain structure and function and behavior of various kinds, the electronic version of the Encyclopedia also makes it possible for the user to observe directly brain and nervous system function and behavior and trace brain circuitry. Special animated maps provide instant information on brain structures and pathways, neurochemical control mechanisms, embryological-developmental principles, etc. But traditional figures and tables also accompany the text of most articles. "Click-on" access to material in related articles in the Encyclopedia, and, through the Internet, to other related papers in the wider literature, gives the reader immediate, flexible access to additional information. In sum, the CD-ROM edition takes advantage of the capabilities provided by the revolutionary new information technology to capture one of the most dynamic areas of modern science. The links that it has to the Internet will enable the Encyclopedia, as a dynamic tool, to keep up with and more accurately report and reflect progress in, the rapidly changing field of neuroscience. The term "neuroscience" is of relatively recent origin. It was probably first used in its present sense by Ralph W. Gerard in the late 1950's. It gained wider acceptance and use after the Neurosciences Research Program (NRP), organized at the Massachusetts Institute of Technology by Francis O. Schmitt in 1962, began its meetings B Work Sessions, Study Programs, Conferences B and publications programs B NRP Bulletin, The Neurosciences: Study Programs 1 B IV,. Neuroscience Research Summaries, etc. In 1969, The Society for Neuroscience was established (it now has 32,000 members!); and with its founding, the term and the field became an established part of the life sciences. Most universities and medical schools now have departments of neuroscience. But what do we mean by "neuroscience"? The word has been defined in various ways during its relatively short history; no formal definition will be attempted here. For our purposes, the word is considered in its broadest interdisciplinary sense. Thus, using "neuroscience" as an umbrella term covering all those sciences trying to understand the brain and nervous system and involved in the investigation of how the brain and nervous system mediate behavior, including the mental and emotional life of humans, any scientist from whatever discipline biomedical, physical, behavioral - interested in trying to understand the mechanisms underlying mind-brain function, may well be considered a neuroscientist. New terms and fields have developed covering different aspects of brain and nervous system research, e.g. neurobiology, cognitive science, neural computing, etc. But we consider all of these simply subsets of the overall, unified "neuroscience". The topics included in the Encyclopedia were selected to reflect this broad view. They are taken from the many fields and subfields, clinical-medical as well as basic, subsumed under the term "neuroscience." The whole spectrum of disciplines from molecular biology to the upper reaches of behavioral medicine are within the province of this publication insofar as they involve efforts to understand how the normal nervous system functions and how its abnormalities and pathologies may be understood and cured or alleviated. As with the earlier editions, our thousand-plus contributors are professional neuroscientists who were invited to write on the basis of their expertise and their contributions to the field. Many are, indeed, the "inventors" of the topic they were asked to describe. Many are the directors of major institutes or departments and laboratories. Most have worldwide recognition. Some have won major awards, and a few, the Nobel Prize. The topics to be covered and the authors to write the articles were selected on the basis of recommendations by our Scientific Advisory Board members as well as our ongoing review of the current literature of neuroscience. Our efforts were supported by library searches using electronic search techniques. Articles have been peer reviewed and carefully edited. Certain papers in this edition were written for an earlier edition by authors who have since passed away. They were selected for republication here for their scientific as well as their historic value. (They are labeled "Classic paper", following the title.) The articles are written for a reasonably broad audience. The Encyclopedia will serve the ready reference needs of neuroscientists and their students and will also meet the needs of all those from other fields who are interested in or directly deal with questions of brain and behavior: undergraduate and graduate students and their teachers in the biomedical sciences; physicians, psychiatrists and psychologists, and other health care specialists including psychotherapists, social workers and nurses; biomedical and electrical engineers; computer scientists; science writers and reporters. Neuroscientists will use the Encyclopedia as a quick source of information, especially on subjects outside their own immediate speciality. For example, a psychiatrist might not need or look to the information in the Encyclopedia on depression or schizophrenia; but he/she might well come to the Encyclopedia for data on visual perception or neurochemistry, neuroscientific areas outside their own immediate speciality. General readers will use the Encyclopedia as a guide to better understanding of the brain and behavior, and of medical advances, achieved and projected, relating to problems that afflict the brain and nervous system. Some of the articles, because of the nature of the subject, are fairly technical; but even the most technical include introductory or background statements that place the topic in the context of the broader field. The authors were invited to review their topics from the context of what the general neuroscience reader, the non-specialist in that particular area, might want to know. (Many of them also generously served as reviewers of the contributions of others.) They were also encouraged to include their own perspectives and insights on the field, and many have emphasized their own findings and contributions. The result is that the Encyclopedia of Neuroscience, in addition to being a ready-reference information and data source, may also be considered a compendium of statements on the development, current status, and future directions of neuroscience from "the inside"; it presents the world of neuroscience and most of its important research and application efforts through the eyes of many of those doing the significant work at this point in history. Neuroscience, as is true of any rapidly moving scientific field, is not without controversy, and many of its most creative and productive investigators are among its most controversial. The Encyclopedia of Neuroscience reflects the differing opinions and special perspectives that are a part of this field. There has been no shying away from controversy when it appeared as an essential aspect of a topic, and the astute reader will readily detect these controversies. Yet most of the authors, as they were requested to do, have tried to present the essentials of their subjects before going into their own particular perspective on issues. The built-in electronic search engines of the Encyclopedia not only make readily accessible the enormous amount of interactive data, but also provide for the consideration and comparison of differing approaches and ideas. Because of its extreme complexity as well as rapid growth, neuroscience necessarily has become compartmentalized into various subspecialties. And, of course, no neuroscientist, however broad gauged, can possibly be expert in all the many levels of neuroscience, from the submolecular to the upper reaches of behavioral analyses. But for practical as well as conceptual (heuristic) analyses, neuroscience also remains a unified, interdisciplinary or multi-level science brought together by its singular, even Promethean goal: understanding how the brain-mind works. That goal is still distant. Neuroscience as a whole is at the critical stage where solid theories, making data coherent and interpretation possible, are sorely needed. We hope that the Encyclopedia of Neuroscience, by clearly and succinctly bringing much disparate data together, may encourage the development of unifying theories and of new conceptual approaches to an understanding of how the brain works. GEORGE ADELMAN BARRY H. SMITH                Copyright © 2004 Elsevier. All rights reserved.