Scientists have been aware for at least one hundred years that each side of the brain controls actions on the opposite side of the body. However, it was not until the 1950s that Roger Sperry (1913–1994) conducted the pioneering research to determine the different functions of the left side and right side of the brain. His experiments contributed to the “split-brain” theory. Sperry received the Nobel Prize in Physiology or Medicine in 1981 for his work.

The spinal cord lies inside the vertebral column. It extends from the occipital bone of the skull to the level of the first or second lumbar vertebra. In adults, the spinal cord is 16 to 18 inches (42 to 45 centimeters) long and 0.5 inches (1.27 centimeters) in diameter. The spinal cord is the connecting link between the brain and the rest of the body. It is the site for integration of the spinal cord reflexes.