My brain is my second-favorite organ.
—Woody Allen, in Sleeper
T he brain forms the essence of what defines us as human beings.To understand its structure and its workings is to understand ourselves.The normal healthy brain is a complex, miraculous, and ingeniously created organ. It permits us to achieve the wonders of music, art, science, architecture, engineering, political organization, and economic structure. Each of us has been endowed with a unique brain with particular capacities that we can either enhance through learning and productive work or waste through intellectual inactivity and unhealthy living habits.We can use our brains to good ends, as when we build bridges or heal illnesses, or we can use our brains to harm or destroy one another in many innovative ways.
The brain can also become “broken” in many ways that lead to the disorders known as mental illnesses. Most of the factors that produce a “broken brain” are outside the control of the individual who develops the illness, although he or she does have “free will” in deciding how to cope with its consequences. In order to understand how disturbances in the brain lead to disturbances in the mind, we need a rudimentary understanding of how the brain is organized and how it works to produce thoughts, emotions, and personal identity.
The human brain is an amazing piece of engineering that allows us to process billions of bits of information within a compact, powerful, continuously changing “living computer” that we carry around on our shoulders our entire lives. It weighs just over two pounds. We each get issued only one.We therefore need to understand its components, how it works, and how we can take good care of it—continually updating its software and keeping its system running smoothly with a minimum of glitches and incompatibilities.
The brain is composed of three types of tissue: gray matter, white matter, and cerebrospinal fluid (CSF).Figure 4-1 shows the differences between these three kinds of brain tissue, as visualized by a routine mag-