Over 30,000 years old, this paleolithic sculpture of a horse was discovered in the Vogelherd caves of southern Germany. Measuring only 5 cm and carved from mammoth ivory, this elegant sculpture is evidence of early human's capacity for remarkable perceptiveness and creativity. (Reproduced, with permission, from the University of Tübingen, copyright for Vogelherd, Horse. Photo: Hilde Jensen.)
During the second half of the 20th century, the central focus of biology was on the gene. Now in the first half of the 21st century, the central focus of biology has shifted to neural science and specifically to the biology of the mind. We need to understand the processes by which we perceive, act, learn, and remember. How does the brain—an organ weighing only three pounds—conceive of the infinite, discover new knowledge, and produce the remarkable individuality of human thoughts, feelings, and actions? How are these extraordinary mental capabilities distributed within the organ? How are different mental processes localized to specific combinations of regions in the brain? What rules relate the anatomical organization and the cellular physiology of a region to its specific role in mentation? To what extent are mental processes hardwired into the neural architecture of the brain? What do genes contribute to behavior, and how is gene expression in nerve cells regulated by developmental and learning processes? How does experience alter the way the brain processes subsequent events, and to what degree is that processing unconscious? Finally, what is the neural basis underlying neurological and psychiatric disease? In this introductory section of Principles of Neural Science, we attempt to address these questions. In so doing, we describe how neural science is attempting to link the logic of neural circuitry to the mind—how the activities of nerve cells within defined, neural circuits are related to the complexity of mental processes.
In the last several decades, technological advances have opened new horizons for the scientific study of the brain. Today, it is possible to link the molecular dynamics of interconnected circuits of cells to the internal representations of perceptual and motor acts in the brain and to relate these internal mechanisms to observable behavior. New imaging techniques permit us to visualize the human brain in action—to identify specific regions of the brain associated with particular modes of thinking and feeling and their patterns of interconnections.
In the first part of this book, we consider the degree to which mental functions can be located in specific regions of the brain. We also examine the extent to which the behavior so localized can be understood in terms of the properties of individual nerve cells and their interconnections in their specific region of the brain. In the later parts of the book, we examine in detail the cognitive and affective functions of the brain: perception, action, motivation, emotion, development, learning, and memory.
The human brain is a network of more than 100 billion individual nerve cells interconnected in systems—neural circuits—that construct our perceptions of the external world, fix our attention, and control the machinery of our actions. A first step toward understanding the mind, therefore, is to learn how neurons are organized into signaling pathways and how they communicate by means of synaptic transmission. One of the chief ideas we shall develop in this book is that the specificity of the synaptic connections established during development underlie perception, action, emotion, and learning. We must also understand both the innate (genetic) and environmental determinants of behavior. Specifically, we want to know how genes contribute to behavior. Behavior itself, of course, is not inherited—what is inherited is DNA. Genes encode proteins that are important for the development and regulation of the neural circuits that underlie behavior. The environment, which begins to exert its influence in utero, becomes of prime importance after birth, and environmental contingencies can in turn influence behavior by altering gene expression.
By means of the merger of molecular biology, neurophysiology, anatomy, developmental biology, and cell biology with the study of cognition, emotion, and behavior in animals and people, modern neural science has given rise to a new science of mind. Along with astute clinical observation, modern neural science has reinforced the idea first proposed by Hippocrates more than two millennia ago that the proper study of mind begins with study of the brain. Cognitive psychology and psychoanalytic theory in turn have emphasized the diversity and complexity of human mental experience. By emphasizing functional mental structure and internal representation, cognitive psychology has stressed the logic of mental operations and of internal representations. Experimental cognitive psychology and clinical psychotherapy can now be strengthened by insights into the neural science of behavior and by imaging mental processes in action in real time. The task for the years ahead is to produce a study of mental processes, grounded firmly in empirical neural science, yet still fully concerned with problems of how internal representations and states of mind are generated.