Curiosity about behavior, both animal and human, is of long standing. The suspicion that substances in the body contribute to behavior also has a long history. During the fifth century b.c.e., Hippocrates suggested, in his humoral theory, that personality was determined by four body fluids: phlegm, black bile, yellow bile, and blood. The dominance of one or another of the fluids was associated with a behavior pattern. A proportionate distribution of the fluids resulted in a balanced personality. This theory has contributed terms such as phlegmatic, sanguine, bilious, and good- or bad-humored to describe personality types and states of mind.
Aristotle (384-322 b.c.e.) is reported to have performed castration experiments on both fowl and men in order to alter behavior. He believed that something produced by the testes caused typically male behavior. Several nineteenth century researchers continued the study of the connection between the testes and male reproductive behavior. In 1849, Arnold Adolphe Berthold initiated a series of experiments on cockerels. He removed the testes from six birds and noted their loss of "male" behavior. Testes were transplanted into the abdomens of half the castrated birds. Successful transplantation restored the typical male crowing and combativeness.
During the late nineteenth and early twentieth centuries, the sciences became more organized. Interest in behavior and its causes continued. The science of ethology, which focuses on animal behavior, came into existence. In the early 1900's, John B. Watson founded a branch of psychology that became known as behavior science. This area of psychology concentrated on human behavioral studies. Eventually, ethology and behavior science contributed to biopsychology, a new branch of psychology which incorporates and applies data from neuroscience, genetics, endocrinology, and physiology in the quest for biological explanations of behavior. Biopsychology em braces several subdivisions. Physiological psychology focuses on nervous system and endocrine system research. Psychopharmacology specializes in the effects of drugs on the nervous system and, ultimately, on behavior. The development of therapeutic drugs is a goal of this discipline. The neuropsy-chologist studies the effects of brain damage on behavior. Psychophysiology differs from physiological psychology in that the psychophysiologist uses only human subjects, while the physiological psychologist experiments on laboratory animals, especially rats.
Early research in physiological psychology focused on the nervous system, but it soon became evident that the endocrine system also influenced behavior and that the effects of the two systems were interrelated contributors to behavior. The endocrine system essentially consists of ductless glands that produce chemical substances called hormones. The hormones elicit physiological reactions, either locally or at some distant target site. When acting at a distance, the hormones travel to the site by way of the circulatory system.
Hans Selye, a Canadian scientist, proposed a direct connection between the endocrine system and behavior. In 1946, he described physiological events that were triggered by stress. This set of bodily changes became known as the general adaptation syndrome. The syndrome involved the mobilization of the autonomic nervous system, the adrenal glands, and the anterior lobe of the pituitary.
As research continued, data on the role of the endocrine system in determining behavior began to accumulate. Researchers continue to look to the endocrine system to provide clues about the causes of psychiatric diseases and the efficacy of hormone therapy in treating the diseases, as well as in altering behavior patterns.
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