|Dale Purves (2009), Scholarpedia, 4(8):7204.||doi:10.4249/scholarpedia.7204||revision #129668 [link to/cite this article]|
Neuroscience is concerned with how the nervous systems of humans and other animals are organized and how they function. This subfield of biology has used many different methods and a wide variety of animal models to advance over the years. Among the most important questions answered during much of the last century concern how the neurons in all nervous systems convey signals from the sensory periphery to inform animals about the external and internal environment; how ensembles of then signal each other in processing this information in the central nervous system; and finally how these ensembles ultimately convey the outcome of neural processing to the body’s effectors (muscles and glands). Although understanding these signaling functions that underlie virtually all neural functions and behaviors was based on anatomical, physiological and biochemical knowledge acquired by many investigators, the pioneers in understanding how information is conveyed over long distances by action potentials were Alan Hodgkin and Andrew Huxley; Bernard Katz whose work revealed how synapses transfer information from one neuron to another and to effector cells; and Stephen Kuffler who participated in both these efforts and made fundamental contributions understanding how peripheral sensory receptors initiate action potentials by responding to energy from different sources in the environment. Biochemical and more recently molecular genetic techniques complemented these largely physiological studies, first identifying an ever increasing number of neurotransmitter agents used at chemical synapses, and ultimately the ion channels activated by these agents as well as the ion channels responsible for action potential conduction. In addition to validating and greatly extending the results of electrophysiology, this knowledge fomented a wealth of clinically oriented neuroscience aimed at better understanding and treating neurological and other diseases by means of improved molecular pharmacology.
Using these electrochemical signals (i.e., receptor potentials, action potentials and synaptic potentials), the brain and the rest of the nervous system carry out an enormous range of operations. In addition to the basic regulatory (homeostatic) functions of nervous systems in all vertebrate and invertebrate animals, the brains of human beings, non-human primates and in varying degrees other animals with highly evolved brains exhibit additional abilities that are loosely referred to as cognitive functions. These functions include perception, attention, learning and memory, emotions, symbolic representation, decision-making, reasoning, problem solving and consciousness. Such abilities are of special interest because they lie at the core of understanding the nature of our own species, its history and its future. Until the last few decades, however, traditional neuroscience was relatively silent on these topics, primarily because there were few tools that could be used to address them. With some notable exceptions, such functions were left to psychology.
Like traditional neuroscience, psychology is a field that took firm root in the late 19th C. In contrast to the explicitly reductionist goals of most neuroscience, the goal of psychology has been to understand ‘mental’ functions and behavior as such rather than their anatomical, physiological and molecular bases. In the absence of significant experimental evidence, the natural philosophers of the 17th and 18th centuries (the predecessors of modern psychologists) had to be content to speculate about these matters. But by the mid- 19th C., many of those drawn to the same interests had become convinced that such issues could and should be studied by means of experimental observation. The pioneers in this domain were Wilhelm Wundt, Hermann Helmholtz, Hermann Ebbinghaus, Gustav Fechner and Ernst Weber. All of these 19th C. investigators strove to make psychology a science, and they succeeded: psychology gradually distinguished itself during the late 19th C. as a discipline in its own right. A further step was the emergence during the 20th C. of cognitive psychology as the subfield of psychology primarily (but not exclusively) devoted to human brain functions. The reason for singling out of human brain functions is that cognition, which literally means ‘the faculty of knowing,’ has often been considered a largely (or by some exclusively) human phenomenon. Thus, cognitive psychology has, de facto, been devoted to understanding those aspects of human mentation that entail conscious awareness and all that goes with it, as opposed to unconscious processes and behaviors generally described as ‘reflexes’.
Since these nominally higher order brain functions and behaviors ultimately depend on the same molecular, cellular and circuit level machinery that had been the focus of traditional neuroscience over most of the 20th C., it made good sense to transcend historical distinctions by joining these fields in common enterprise. This convergence, which has accelerated during the last 30 years, has gradually defined a new field dubbed ‘cognitive neuroscience’. The increasing impetus to bring together traditional neuroscience and psychology despite their separate interests and traditions is straightforward. As many of the key problems in traditional neuroscience were solved to a reasonable level of satisfaction, investigators in traditional neuroscience increasingly aspired to understand more complex neural functions (human brain functions in particular) with the powerful electrophysiological, anatomical, biochemical and molecular genetic tools they had developed. At the same time, cognitive psychologists increasingly aspired to closer ties with concepts and methods of neuroscience as a means of advancing their long-standing agenda of understanding mental processes. The rapid emergence of cognitive neuroscience over the last two or three decades is thus a logical step for both traditional neuroscience and psychology, driven by increasingly powerful non-invasive methods for studying the brains of normal subjects. These methods include electroencephalography, positron emission tomography, functional magnetic resonance imaging, magneto-encephalography and trans-cranial magnetic stimulation. Traditional neuroscience and psychology are thus inexorably moving toward a tighter union, and for good reasons. A sound working knowledge of brain structure and the basic physiology, chemistry and genetics of its elements are essential in understanding what human brains ultimately do, and psychologists who fail to respond to this requirement will be left behind. At the same time traditional neuroscientists who do not look beyond the molecular and cellular levels will be seen as not leading the field towards its full potential.
A final component that has been added to the mix of neuroscience during the last few decades is theoretical science. The advent of computers as analytical tools for dealing with complex electrophysiological, molecular and image datasets in the 1970s has been followed by the increasing use of computer modeling and computer simulations of many brain functions. These approaches have gradually entered the mainstream of work in neuroscience, defining yet another subfield. In the last few years virtual reality paradigms have further extended theoretical computational approaches as more paradigms have been developed for the training or even evolving autonomous neural networks that can serve as proxies for animal nervous systems.
The many unanswered questions about how the brains work, the intrinsic fascination of these issues and the misery that continues to be inflicted by the nervous systems' many pathologies insure that neuroscience, now defined by the amalgamation of several previously distinct disciplines, will flourish for many years to come.
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