system by manipulating it or probing it in some direct way? Some twenty years ago the answer to this question would probably have been "No"; and there is a very good reason why this view might have been held, especially by students of the mammalian nervous system. At that time most investigators used anaesthetised animals, or animals immobilized in some other way such as by surgically isolating the brain from the spinal cord, by dividing the brain at various levels or through the use of paralyzing agents. These con­ ditions achieved two things. On the one hand, they allowed sub­ stantial advances to be made, particularly in the analysis of sensory processing and in the analysis of the neuronal mechanisms of relatively simple reflex action. On the other hand, the experi­ mental conditions virtually eliminated complex behavior.