Physiological Approach

Historical Background

Early thinking about the physiology of the mind focused on determining the anatomical structures involved in the operation of the mind. In the 4th century B.C.E., the philosopher Aristotle (384–322 B.C.E.) stated that the heart was the seat of the mind and the soul. The Greek physician Galen (ca. 130–200 C.E.) saw human health, thoughts, and emotions as being determined by four different “spirits” flowing from the ventricles—cavities in the center of the brain. This idea was accepted all the way through the Middle Ages and into the Renaissance in the 1500s and early 1600s. In the early 1630s, the philosopher Rene Descartes, although still accepting the idea of flowing spirits, specified the pineal gland, which was thought to be located over the ventricles, as the seat of the soul.

In 1664, Thomas Willis, a physician at the University of Oxford, published a book titled The Anatomy of the Brain, which was based on dissections of the brains of humans, dogs, sheep, and other animals. Willis concluded that the brain was responsible for mental functioning, that different functions were located in different regions of the brain, and that disorders of the brain were disorders of chemistry. Although these conclusions were correct, details of the mechanisms involved had to await the development of new technologies that would enable researchers to more accurately observe the brain's structure and to record electrical signals in the nervous system.

By the late 1800s, researchers had shown that a wave of electricity is transmitted in groups of neurons, such as the optic nerve. To explain how these electrical signals result in different perceptions, Johannes Müeller in 1842 proposed the doctrine of specific nerve energies, which stated that our perceptions depend on “nerve energies” reaching the brain and that the specific quality we experience depends on which nerves are stimulated. Thus, he proposed that activity in the optic nerve results in seeing, activity in the auditory nerve results in hearing, and so on. By the end of the 1800s, this idea had expanded to conclude that nerves from each of these senses reach different areas of the brain. This idea of separating different functions is still a central principle of nervous system functioning.

Details about how single neurons operate had to await the development of electronic amplifiers that were powerful enough to make the extremely small electrical signals generated by individual neurons visible. In the 1920s, Edgar Adrian was able to record electrical signals from single sensory neurons, an achievement for which he was awarded the Nobel Prize in 1932.

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