This book is a collection of papers describing some of the first attempts to apply the techniques of recombinant DNA and molecular biology to studies of the nervous system. We believe this is an important new direction for brain research that will eventually lead to insights not pos sible with more traditional approaches. At first glance, the marriage of molecular biology to brain research seems an unlikely one because of the tremendous disparity in the histories of these two disciplines and the problems they face. Molecular biology is by nature a reductionist approach to biology. Molecular biologists have always tried to attack central questions in the most direct approach possible, usually in the most simple system available: a bacterium or a bacterial virus. Important experiments can usually be repeated quickly and cheaply, in many cases by the latest group of graduate students entering the field. The success of molecular biology has been so profound because the result of each important experiment has made the next critical question obvious, and usually answerable, in short order. Studies of the nervous system have a very different history. First, the human brain is what really interests us and it is the most complex structure that we know in biology. The central question is clear: How do we carry out higher functions such as learning and thinking? How ever, at present there is no widely accepted and testable theory of learn ing and no clear path to such a theory."