What is the brain? The answer to this question depends upon who is asked.

The anatomist, focusing on structure, may answer,

"a collection of specialized cells, complexly arranged yet with commonalities." The physiologist, whose concern is processes, may answer, "an electrochemical mechanism that interacts with its environment and itself in particular ways." And the chemist perhaps says, "an incredible bio- chemical system specialised for the processing of information." To the non- professional, the brain is rarely given much thought (although it is the source of all thought), but virtually everyone could agree that all human behavior is generated by the brain, to be expressed by muscles and glands, as well as all human thought, emotion, memory, and knowledge. The hypothetical answers above, from an anatomist, a physiologist, and a chemist, represent the three basic sciences upon which the brain sciences, or neurosciences rest. While individual scientists' goals differ, and all desire to know more of the workings of the brain, it is useful to remember that most scien- tists are interested in answering the following questions:

• What are the components of the brain, and how are they connected one to another?
• What are the functions of those components, and how do they work together?
• What are the chemical and electrical phenomena underlying the functioning of these components?