This document provides an introduction to physiological psychology. It defines physiological psychology as the branch of biological psychology that deals with the workings of the mind and body and how the brain relates to behavior. It explains that physiological psychology studies how bodily functions are directly linked to the brain and how small changes in the brain can affect behavior. The document then discusses some important figures in the history of the field, including Hippocrates' idea that emotions originate in the brain, Galen's theories about brain functions and personalities, Descartes' view of the body as a machine responding to stimuli, and Muller's ideas about nerve fibers relaying messages between the brain and body.