This book originated in a NATO Advanced Science Institute held at Il Ciocco, Italy, on September 1 — 10, 1996. The Institute was entitled ''The Role of the Corpus Cal-losum in Sensory-Motor Integration: Anatomy, Physiology and Behavior; Individual Differences and Clinical Applications." There were nearly 100 participants from 25 countries, including leading researchers on callosal structure and function. Most of the participants in the ASI contributed to this volume. Their original contributions were written in 1996, but all have been revised and updated in 1999-2000. A few additional contributors were invited to write new chapters on emerging relevant topics, notably neuroimaging.

This volume, however, is not a conference proceedings. Instead, it is meant to provide a unique perspective on the emerging field of Cognitive Neuroscience. It is designed to do so in two ways. First, it summarizes the state of the art of research on the human corpus callosum. Such treatment is sorely necessary because it has been at least a decade since the publication of the most recent overview. One can trace the development of human neuropsychology through the study of the corpus callosum, which, in turn, illuminates the study of hemispheric specialization. Hemispheric specialization remains a core problem in human neuropsychology because it recapitulates any aspect of the human condition, from perception and emotion to memory and language. Furthermore, hemispheric specialization and interhemispheric interaction serve as a model system for a fundamental problem of cognitive neuroscience: the problem of modularity and of intermodular communication. The study of the corpus callosum brings to this problem a neuroscientific arsenal, including neuro-anatomy, neurophysiology, and behavior. The evolution of this study can be traced through a series of classical books, all based on conference proceedings, starting with Mountcastle's 1962 edited volume, Interhemispheric Relations and Cerebral Dominance, continuing with Russell, van Hof, and Berlucchi's 1979 edited volume, Structure and Function of Cerebral Commissures, and concluding with, Lepore, Ptito, and Jasper's edited 1986 volume, Two Hemispheres—One Brain: Functions of the Corpus Callosum. These volumes tend to be spaced a decade apart, and we are now overdue for the next installment. This book is meant to serve that role.

The second way this book is designed to provide a perspective on cognitive neuroscience is as an advanced didactic introduction to the field. Instead of providing a standard introduction by discussing the various systems of the mind/brain, such as perception, action, emotions, memory, language, and problem solving, this book uses the case study approach. It focuses on the simplest possible sequence of perception-decision-action as it occurs in the simple reaction time paradigm of Poffenberger (1912). The task could not be simpler: Press a button with one hand as soon as you detect a patch of light in the periphery of the visual field. But when the patch occurs in the visual field opposite to the responding hand, there must have occurred inter-hemispheric transfer prior to response. Transfer of what? A visual input code? A

cognitive decision code? A motor response code? The book studies this task by considering, in turn, anatomical, physiological, and behavioral approaches, and by combining animal models, normal human studies, and evidence from clinical populations. In this way, the book introduces the basic methods of cognitive neuroscience, not in isolation but by focusing on the same central paradigm and problem. Learning best occurs in context, when attempting to answer a specific question. This book provides such a question-centered approach to cognitive neuroscience.

The format of the book is didactic and dynamic. Each of the five parts—anatomy, physiology, behavior, clinical studies, and a case study of pure alexia—includes several chapters that introduce the main findings, followed by commentaries that discuss and amplify those presentations. Each part concludes with an editorial commentary that summarizes the presentations and puts them in a larger context. These commentaries are also used to extend the coverage to more cognitive approaches.

The view that emerges from the book is that simple reaction time is not simple at all. The corpus callosum seems to consist of many parallel interhemispheric channels for communication and control. Even sensorimotor cross-callosal transfer is context-dependent and modulated by attention. This permits the two cerebral hemispheres to assume any of a variety of states or degrees of mutual independence. And that variety makes possible diverse cognitive processes.

This book owes its birth to NATO for generously making possible the original meeting in the true spirit of international cooperation. But our deepest debt is to the participants of the meeting, speakers and audience alike, who created a warm interactive atmosphere of a shared enthusiastic scientific exploration. Last but not least, that exploration was aided immensely by the scenery, food, and wine of Tuscany.

This work was supported in part by NIH grant NS 20187. Linda Capatillo-Cunliff was indispensable in organizing the meeting. Ian Gizer, Eric Mooshagian, and AnThu Vuong provided assistance in preparing the manuscript. Special thanks also to Dr. Joseph Janeti for advice and support throughout this project. Finally, we are indebted to Michael Rutter and Sara Meirowitz from MIT for their dedicated editorial assistance.

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