The Book of Hebb

in the cerebrum: " ... we know practically nothing about what goes on between the arrival of the excitation at a sensory projection area and its later departure from the It has been 50 years since Donald Hebb published the motor area of the cortex " (xvi). Hebb conjectured that Organization of Behavior: A Neuropsychological Theory cortical circuits admit self-sustaining activity that rever-in 1949. This book was written at a time when behavior-berated in what he called " cell assemblies. " This idea ism was dominant in North American psychology. The was inspired by evidence for recurrent connections be-approach that Hebb advocated, based on what was tween neighboring cells in the cortex. Although rever-then known about the brain, was out of favor among beratory activity lasting for up to half a second had psychologists who believed that only external sensory been observed by Lorente de Nó , Hebb went further stimuli and motor responses ought to be included in and suggested that such activity in one cortical circuit any explanation of behavior. Most neuroscientists have could through converging projections activate other ar-heard about the " Hebb synapse, " but few know why he eas of cortex and lead to a sequence of activations he postulated this learning rule. This is a good time to take called a " phase sequence. " Although these ideas remain a closer look at this book and let Hebb speak for himself. highly speculative, they reflect recent issues such as Hebb was on the faculty of the Psychology Depart-spike timing and spike synchrony that today are at the ment at McGill University. One of his research interests forefront of theoretical research on the cortical neural was the behavioral effects of brain lesions, and he had code (Abbott and Sejnowski, 1999). collaborated with Wilder Penfield, a colleague at McGill, Hebb needed a way to sustain persistent reverbera-but he was more broadly interested in the development tory activity (a " trace ") in cortical circuits. He proposed of behavior and learning, which he saw as intimately that patterns of connections between neurons could related. In 1949, much of what we now take for granted sustain reverberatory activity if their strengths could be about the organization of the nervous system and the adjusted by an activity-dependent mechanism for syn-properties of neurons was not yet discovered. Hodgkin aptic plasticity that he called a " Neurophysiological Pos-and Huxley's landmark series …