Chapter 5 Introduction

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A human brain is, we must admit, somewhat disappointing in appearance. It’s about the size and shape of a cantaloupe, but more gnarled. As described by Rita Carter in her book Mapping the Mind (1999), it is “as big as a coconut, the shape of a walnut, the color of uncooked liver, and the consistency of chilled butter” (p. 15). To the eye it seems relatively dormant, even when viewed in a living person. Aristotle and many other ancient Greeks—who were among the first to try to figure out what the various parts of the body are for—were not much impressed by the brain. Noticing that the blood vessels leading into it are larger than those entering other organs, they suggested that the brain’s main function was to cool the blood. They were much more impressed by the heart, an obviously dynamic organ, and proposed that the heart and blood are the source of feelings, thoughts, and all else that we today call “psychological.”

Not all of the ancients agreed with the heart theory of psychology, however. One who didn’t was the Greek physician Hippocrates, whose observations of the effects of head injuries on people’s thoughts and actions led him to focus on the brain. In the fourth century bce, Hippocrates (1923) wrote: “From the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, griefs and tears. Through it, in particular, we think, see, hear…. Eyes, ears, tongue, hands and feet act in accordance with the discernment of the brain” (p. 175).

Hippocrates was right, of course, and that is why nearly every introductory psychology text, from William James’s (1890/1950) classic on, contains a chapter about the nervous system, especially the brain. As psychologists and neuroscientists learn more about the brain, the nervous-system chapter becomes ever more meaningfully connected to the rest of the book, and material on the brain spills ever more copiously out of that chapter into others. In a real sense, psychology is the study of what the nervous system does; indeed, psychology focuses on the most complex aspects of what the nervous system does.

Every chapter of this book is at least indirectly about the nervous system, and this chapter is directly about it. The chapter begins with discussions concerning the basic units of the nervous system—individual neurons—and how they communicate with one another. Then it moves to descriptions of each of the larger structures of the nervous system, focusing on their roles in controlling behavior. The final section deals with the ways in which the brain changes over time: an examination of brain processes involved in learning and a brief look at the evolution of the brain. These discussions all provide background for many discussions of brain processes that you will come across in later chapters.