Lashley, Karl Spencer (1890-1958), was an American psychologist known for his research on the function of the brain in relation to behavior. Lashley developed two main principles as a result of his research. The first, the principle of mass action, states that in many types of learning the cerebral cortex acts as a whole. The second principle, the principle of equipotentiality, states that certain small areas of the brain can take on the function of larger, related areas that have been destroyed.
Lashley was born in Davis, West Virginia. He received a Ph.D. in zoology from Johns Hopkins University in 1914. Lashley taught at the universities of Minnesota and Chicago and at Harvard University. From 1942 to 1955, he served as director of the Yerkes Laboratories of Primate Biology in Orange Park, Florida.
