章一摘录

THE LAST FRONTIER OF THE BIOLOGICAL SCIENCES–the ultimate challenge–is to understand the biological basis of consciousness and the brain processes by which we feel, act, learn, and remember. During the past few decades, a remarkable unification within the biological sciences has set the stage for addressing this great challenge. The ability to sequence genes and infer the amino acid sequences of the proteins they encode has revealed unanticipated similarities between proteins in the nervous system and those encountered elsewhere in the body. As a result, it has become possible to establish a general plan for the function of cells, a plan that provides a common conceptual framework for all of cell biology, including cellular neural science. The current challenge in the unification within biology, which we outline in thisbook, is the unification of the study of behavio–the science of the mind–and neural science–science of the brain.
Such a unified approach,i n which mind and body are not viewed as separate entities, rests on the view that all behavior is the result of brain function. What we commonly call the mind is a set of operations carried out by the brain.
    How do the billions of individual nerve cells in the brain produce behavior and cognitive states, and how are those cells influenced by the environment, which includes social experience? Explaining behavior in terms of the brain's activities is the task of neural science, and the progress of neural science in explaining human behavior is a major theme of this book.
    Neural science must continually confront certain fundamental questions. Is a particular mental process carried out in specific regions of the brain, or does it involve the brain as a whole? If a mental process can be localized to discrete brain regions, what is the relationship between the functions of those regions in perception, movement, or thought and the anatomy and physiology of those regions?Are these relationships more likely to be understood by examining each region as a whole or by studying individual nerve cells?
    In the late 1820s Gall's ideas were subjected to experimental analysis by the French physiologist Pierre Flourens. By systematically destroying Gall's functional centers in the brains of experimental animals, Flourens attempted to isolate the contribution of each "cerebral organ" to behavior. From these experiments Flourens concluded that specific brain regions are not responsible for specific behaviors, but that all brain regions, especially the cerebral hemispheres of the fore-brain, participate in every mental operation. Any part of a cerebral hemisphere, Flourens proposed, is able to perform all the hemisphere's functions. Injury to anyone area of the cerebral hemisphere should therefore affect all higher functions equally. Thus in 1823 Flourens wrote: "All perceptions, all volitions occupy the same seat in these(cerebral) organs; the faculty of perceiving, of conceiving, of willing merely constitutes therefore a faculty which is essentially one."
    The holistic view was seriously challenged, however, in the mid-19th century by the French neurologist Paul Pierre Broca, the German neurologist Carl Wernicke, and the British neurologist Hughlings Jackson. For example, in his studies of focal epilepsy, a disease characterized by convulsions that begin in aparticular part of the body, Jackson showed that different motor and sensory functions could be traced to specific parts of the cerebral cortex. The regional studies of Broca, Wernicke, and Jackson were extended to the cellular level by Charles Sherrington and by