Galen's ideas on neurological function.

Galen was the leading physician of the Roman empire during the last half of the second century. Unlike some of his predecessors, Galen concluded that the brain controlled cognition and willed action. The initial evidence for this doctrine was that the brain was the site of termination of all of the five senses: touch, taste, smell, sight, and hearing. Galen presumed that the information from these five senses was organized by a part of the brain that generated a concept of an object common to all senses; this part of the brain he considered to be the area of common sense. Galen thought that he could differentiate sensory from motor nerves (not nerve fibers) by palpation. Sensory nerves were soft because they needed to be impressed with the essence of the object seen, heard, felt, smelled, or tasted. Motor nerve fibers were very hard because they needed to carry the force of the will from the brain to the muscles. Strong willed people had especially firm motor nerve fibers; hence, the modern term that a person with great bravery has 'nerves of steel'. Galen considered that common sense, cognition, and memory were functions of the brain. Personality and emotion were not generated by the brain, but rather by the body as a whole (or perhaps by the heart and liver). Galen's studies of respiration and of the recurrent laryngeal nerve solidified the knowledge that the brain, not the chest, was the site of the rational power that guides human behavior. This doctrine has continued from Galen's time to the present.