In our lives as educated philosophers, poets, and parents, we want to know how the building blocks of the brain, its individual neurons, produce ideas, feelings, and consciousness. As experimental neuroscientists, we know that these are very difficult questions to answer. The brain clock, located in the suprachiasmatic nucleus (SCN) of all mammalian brains provides us with a window into experimental studies of how behavior emerges from the activity of the elements of the brain – its molecules, genes, cells and circuits. The exploration of daily oscillations, manifest at the level of the cell, the tissue, and the whole animal enable understanding of emergent properties of brain function. At each level of analysis, responses to variations in operating environment (robustness), and responses that occur following damage to components of the system (resilience), provide insight into the mechanisms whereby the SCN achieves its brain clock functions. Tissue level rhythmicity reveals circuits associated with an orderly spatio-temporal daily pattern of activity that is not predictable from its cellular elements. In stable state, some SCN cells express low amplitude or undetectable rhythms in clock gene expression while others produce high amplitude oscillations. Within the SCN, clock gene expression follows a spatially-ordered, repeated pattern of activation and inactivation which produce our daily rhythms of arousal and sleep. Studies of clock gene expression within cells indicate that individual neurons are organized into nodes or subsystems that are themselves sequentially activated across the volume of the SCN in a cycle that repeats on a daily basis. Just as daily rhythms at the cellular level depend on sequential expression and interaction of clock genes, so too do rhythms at the SCN tissue level depend on sequential activation of local nodes. Brain clock function emerges from the repeated use of similar cellular oscillators as elements, with seemingly minor modifications having seemingly large consequences as these elements are wired together.
Dr. Rae Silver is the Helene L. and Mark N. Kaplan Professor of Natural and Physical Sciences in the Psychology Department at Barnard College, Professor of Psychology in Columbia University's Psychology Department, and Professor of Psychology in the Department of Anatomy and Cell Biology at the Columbia College of Physicians and Surgeons, all in New York, NY. She studied physiological psychology at McGill (BSc Honours, 1966) and biopsychology at the City University of New York (MA, 1970) and at the Institute of Animal Behavior at Rutgers University (PhD, 1972, under Daniel S. Lehrman). Before becoming a Professor at Barnard College and Columbia University in 1982, she held positions at Rutgers (1972-74), Hunter College of the City University of New Yotk (1974-76), the American Museum of Natural History (1974-76) and Barnartd College of Columbia University (1976-82). An expert in medical and biological aspects of the internal body clock, Dr. Silver is the (co-)author of almost 200 scientific publications and holds many awards.