White matter fiber architecture of the human brain, showing the corpus callosum and brainstem pathways. The image was constructed from magnetic resonance (MR) imaging data with the diffusion spectrum imaging technique, which uses the rate and preferred direction of diffusion of water molecules to generate contrast in MR images to reveal bundles of axons traveling in fiber tracts. The fibers are color-coded by direction: red, left-right; green, anterior-posterior; blue, ascending-descending (RGB = XYZ axes). From the Connectome Scanner dataset. (From the Connectome Scanner dataset. Courtesy of the USC Laboratory of Neuro Imaging and Athinoula A. Martinos Center for Biomedical Imaging. Consortium of the Human Connectome Project— www.humanconnectomeproject.org.)
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 focus has shifted to neural science, and specifically to the biology of the mind. We wish to understand the processes by which we perceive, act, learn, and remember. How does the brain—an organ weighing only 1.5 kg—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? What rules relate the anatomical organization and the cellular physiology of a region to its specific role in mentation? 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 are the neural bases of neurological and psychiatric disorders? In this introductory section of Principles of Neural Science, we begin to address these questions. In so doing, we describe how neural science attempts to link the computational logic of neural circuitry to the mind—how the activities of nerve cells within defined neural circuits mediate complex mental processes.
Over the past several decades, technological advances have opened new horizons for the scientific study of the brain. Today, it is possible to link the cellular dynamics of interconnected circuits of neurons 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 localized to specific regions of the brain. We also examine the extent to which such functions can be understood in terms of the properties of individual nerve cells, their molecular constituents, and their synaptic connections. In the later parts of the book, we examine in detail the mechanisms underlying cognitive and affective ...