Even before the time of organized scientific investigation, hu­ mans had begun pondering and attempting to explain the work­ ing of the brain and the mental and behavioral states it produces. In the last twenty years there has been an almost explosive in­ crease in brain research. Beginning perhaps with the pioneering efforts of Francis O. Schmitt to establish the Neuroscience Re­ search Program and the later development of the Society for Neuroscience, there has emerged a large and powerful multi­ disciplinary research force devoted to understanding even the ru­ dimentary aspects of brain functioning. Chemists, physicists, and engineers with their special expert­ ise in quantitative physical measurements have teamed up with the neurobiologists, who best know the texture and design of brains, to produce particularly effective new approaches. No­ where is this more evident than in the recently developed meth­ ods like positron emission tomography and magnetic resonance imaging-techniques that allow one to observe on-going brain ac­ tivity in humans. This volume concerns a considerably more modest approach: the use of microelectrodes to electrochemically monitor certain aspects of chemical dynamics in functioning ani­ mal brain systems. The method provides signals that can be di­ rectly related to chemical neurotransmission. It is a relatively new technique, the first practical measurements having been made in the 1970s, and it is continuously undergoing refinement. The organizer of this book, Jay Justice, is eminently qualified for the task.