First published in 1982. The human brain is the most complex object on Earth that can be studied scientifically: a collection of over 100 billion neurons squeezed into a space about the size of a grapefruit, which somehow is able to control all that you feel, do, and know. There still is little understanding of the most important and interesting functions of the brain, such as what really happens up there when you learn something, when you are thinking, or when you are feeling happy. In this book the author attempts to organize nearly the entire field of psychology within a single new theory, based upon only one very simple assumption about neuronal functioning.