Karl Spencer Lashley

An American neuropsychologist who demonstrated relationships between animal behavior and the size and location of brain injuries, summarizing his findings in terms of the concepts of equipotentiality and mass action.

Karl Spencer Lashley was born at Davis, West Virginia, on June 7, 1890. As a child he was interested in animals, an interest which continued throughout his adult life. His mother, Maggie Lashley, encouraged him in his intellectual pursuits. After studying at the University of West Virginia and then taking a master's degree in bacteriology at the University of Pittsburgh, Lashley did doctoral and postdoctoral research at Johns Hopkins University. While at Hopkins, he was influenced by the zoologist H. S. Jennings, the psychiatrist Adolf Meyer, and the psychologist John B. Watson, the father of behaviorism.

Lashley was at once an experimental researcher and a psychological theoretician. His investigations were published in the leading journals and proceedings of major scientific societies. After several joint studies with Jennings, Lashley published his own thesis, “Inheritance in the Asexual Reproduction of Hydra.” He collaborated with Watson in studying behavior in seabirds, acknowledging Watson's behavioristic approach the rest of his life.

Collaborating with Shepherd Ivory Franz, Lashley produced several papers on the effects of cerebral destruction upon retention and habit formation in rats. This was the beginning of his preoccupation with one of the persistent problems in psychology, that of cerebral localization. Earlier researchers Gall, Broca, Fritsch and Hitzig, Ferrier, and Munk were all believers in exact cerebral localization whereas Flourens, Goltz, and Franz doubted it. Lashley did a series of experiments using rats trained to run a maze. He removed or damaged small parts of their brains, but there was no area that damaging it seemed to remove the memory of how to run the maze. This provided strong evidence that memory, at least, was not a localized function of the brain.

The culmination of his localization experiments was Brain Mechanisms and Intelligence: A Quantitative Study of Injuries to the Brain (1929), his longest, most significant monograph. In it he summarized his concepts of equipotentiality and mass action and marshaled the experimental evidence to support them. Thus he accounted for the absence of precise and persistent localization of function in the cortex. Lashley's experiments denied the simple similarity and correspondence, previously assumed, between associationistic connectionism and the neuronal theory of the brain as a mass of neurons connected by synapses.

In addition to his research, Lashley taught as professor of psychology at the universities of Minnesota and Chicago and at Harvard University. He held various honorary positions and lectureships, was on the editorial boards of numerous scientific journals, served as member of and adviser to governmental committees, and was elected to many scientific and philosophical societies. He died on August 7, 1958, in Poitiers, France.



Andrewes, David. Neuropsychology: From Theory to Practice Hove, UK: Psychology Press, 2016.

Beach, Frank A. Karl Spencer Lashley Washington, DC: National Academy of Sciences, 1961.

Lashley, Karl. Brain Mechanisms and Intelligence: A Quantitative Study Chicago: University of Chicago Press, 1929.

Orbach, Jack. The Neuropsychological Theories of Lashley and Hebb Lanham, MD: University Press of America, 1998.

Orbach, Jack. Neuropsychology After Lashley: Fifty Years Since the Publication of Bran Mechanisms and Intelligence Hillsdale, NJ: Lawrence Erlbaum Associates, 1982.

Weidman, Nadine. Constructing Scientific Psychology: Karl Lashley's Mind-Brain Debates New York: Cambridge University Press, 2006.