Lashley, Karl S.

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Lashley, Karl S.

Work on brain function

Work on sensory functions

Work on neural functions



Karl Spencer Lashley (1890–1958), American psychologist, was born in Davis, West Virginia, of middle-class English stock. His father, Charles Gilpin Lashley, was the manager of the family store in Davis and the founder of a small bank there; at various times he served in such political posts as mayor and postmaster. Lashley’s mother, Maggie Blanche Spencer, was descended from Jonathan Edwards, the philosopher, theologian, and educator of American revolutionary times; she had been a country schoolteacher before her marriage. After that she continued to be an avid reader, amassing a personal library of more than 2,000 volumes, and was an informal “adult education” instructor in diverse subjects. She appears to have been responsible for cultivating Lashley’s love of nature and of learning.

Except for four years, from 1894 to 1898, during which the family, afflicted with “gold fever,” trekked to the west coast and Alaska, Lashley spent his early years in Davis. He showed signs of being a prodigy. During his elementary school years, his interest in nature and animal behavior was already evident in his collection of all sorts of plants and animals, including many pets. During this period, too, his marked mechanical aptitude became apparent; he expertly designed many gadgets, small and large, and made them in his own workshop.

Graduating from Davis High School at the age of 14, he entered the University of West Virginia, but because his high school was unaccredited he had to spend a year in preparatory work before becoming a freshman. Although vaguely inclined toward engineering, he enrolled, at his mother’s wish, in a liberal arts program, intending to major in Latin or English. It was only to fill an unscheduled hour that he enrolled in a course in zoology taught by John Black Johnston (later dean at the University of Minnesota when Lashley taught there). This contact with Johnston crystallized his interest in zoology for, as he later wrote, “Within a few weeks in this class I knew that I had found my life’s work” (Beach 1961).

After Lashley’s freshman year Johnston left and was succeeded by Albert M. Reese, who appointed Lashley departmental assistant. In this role he found a fascinating Golgi series of frog brain sections and proposed to “draw all the connections between the cells.” To his surprise, most of the cells were not stained and therefore not visible. He later commented, “... I think almost ever since I have been trying to trace those connections” (ibid., p. 169). Lashley went on to take all the courses offered by Reese, the only zoologist on the faculty, but he got much of his education in zoology by independently working out projects for which Reese gave only the briefest instructions. Lashley’s philosophy of education and handling of his own students reflected this experience with independent work.

In 1910, with a B.A. in zoology, Lashley went to work on a master’s degree at the University of Pittsburgh, where he had been awarded a teaching fellowship in biology. It was here that he took his only formal course in psychology. This was a laboratory course in experimental psychology taught by Karl Dallenbach who later wrote, “Lashley was intensely interested and was the outstanding student in the class.... He showed in that course the promise that he later fulfilled” (ibid., p. 170).

Lashley received his master’s degree in June 1911 and went that summer to Cold Spring Harbor to do research on the variability in the number of cirri in the ciliate Stylonychia. (Cold Spring Harbor is a prominent Long Island center for biological research; during the summer months many outstanding academic biologists work there.) This research led to his appointment by H. S. Jennings as a teaching fellow in zoology at Johns Hopkins University. There Lashley worked with Jennings on paramecia and with S. O. Mast on the behavior of various invertebrates, taking his PH.D. in 1914 with a dissertation on inheritance in asexual reproduction of Hydra. During this period he also pursued his interest in psychology, working with Adolph Meyer, professor of psychiatry and director of the newly established Phipps Clinic, and with John B. Watson, then professor of psychology.

Watson’s behavioristic approach had tremendous appeal for Lashley and led him to do postdoctoral work on vertebrate behavior. This work extended over three years, from 1914 to 1917, during which he slowly formulated and launched the rich program of research and writing he was to carry on for the rest of his life. The first two years he held successive appointments in zoology as Bruce fellow and Johnston scholar but worked with Watson on a variety of problems: field experiments on reproductive behavior of terns (in the Dry Tortugas), acquisition of human motor skills, color vision in birds, conditioning of the salivary reflex, and effects of strychnine and other drugs on maze learning in rats.

While pursuing these experiments, Lashley became interested in the work of Shepard Ivory Franz, who was examining the behavior of brain-injured patients at Saint Elizabeths Hospital in Washington, D.C. Franz was also inaugurating work on the behavioral effects of experimental brain lesions in animals. After frequent journeys to Washington to observe this work, Lashley was permitted to study neurological cases in the wards and to acquire the necessary surgical and histological skills for performing studies of the neural basis of learning. Here he got started solidly on the research career that eventually brought him eminence and recognition.

By the fall of 1917 the United States had entered World War i, and many psychologists were in the army or heavily involved in war-related activities, but Lashley’s vision was too poor to meet army standards. Therefore, when he had completed his period of postdoctoral training, he accepted a post at the University of Minnesota arranged by Robert M. Yerkes, who was slated to become chairman there at the war’s end but never did. Morale in the department was not high, and after one year Lashley, taking a leave of absence, accepted a position with the U.S. International Hygiene Board. Although he was working once again with Watson, this time in a program dealing with public education on the dangers of venereal disease, this assignment was not a productive one, and in 1920 R. M. Elliott, the new chairman of the department of psychology, prevailed on Lashley to return to the University of Minnesota as assistant professor.

Lashley’s intellectual pre-eminence and prolific research on brain function brought him rapid promotion: in 1924, at the age of 34, he was made a full professor. In 1926 he left Minnesota for Chicago, at first serving as research psychologist with the Behavior Research Fund at the Institute for Juvenile Research and later, in 1929, moving to a professorship at the University of Chicago. In 1935 he went to Harvard University as professor and in 1937 was made a research professor in neuropsychology, a title he held until his retirement in 1955. However, in 1942, in a joint arrangement with Yale University and certain private foundations, he moved to Florida as director of the Yerkes Laboratories of Primate Biology.

It has been said of Lashley that he was an “inspiring teacher who described all teaching as useless” (Beach 1961, p. 163). He himself frequently asserted that “those who need to be taught can’t learn, and those who can learn don’t need to be taught” (ibid., p. 182). He applied this principle by eschewing formal teaching, often raising artificial barriers to registration in his courses. Because his research was so excellent, he managed better than any other academic psychologist of his time to stay out of the classroom. The few lectures he did give were usually stimulating, often exciting. And in seminars he had few peers; he was an impressive scholar, with a pleasant wit and a fascinating intellect. Like Mark Hopkins, however, he was at his best “on a log.” He was always available to graduate students and postdoctoral fellows in his laboratory, and for scores of psychologists their informal contacts with Lashley were to be the most significant periods of their education. In this way Lashley was a great teacher even though fewer students, probably, have studied under him formally than under any other psychologist of distinction.

One other related characteristic of Lashley’s deserves mention. This was his “go-it-alone” attitude toward research. He had fewer collaborators and published fewer joint papers than most other comparable scientists. Except for very routine work, he did all his own research, “running” his animals, doing data analysis, making histological reconstructions, and writing his own papers. He expected the same of others working with him. He never directed but only advised when his advice was asked. He felt strongly that research of quality must be carried out by scientists of quality, not by a host of assistants and graduate students. It is easy, therefore, to understand his dismay at the increasingly large amounts of money being employed in organized research. Writing in 1953 to Watson, Lashley said, “The money available for research now is rather shocking. The man who doesn’t have $20,000 per year for research is probably intellectually honest. There are not enough competent men to spend the money” (ibid., p. 180).

Work on brain function

Lashley’s most productive phase was launched in his work with Franz. At first he merely took for granted the connectionism of Watsonian behaviorism and looked for the neural basis of the connections. This, however, proved elusive, for in study after study in the 1920s he obtained data suggesting a field theory rather than a connectionist theory of brain function.

Lashley’s reasoning and his findings in these studies should be briefly summarized. Connectionist theory holds that complex behavior is made up of conditioned reflexes, each forming a connection through the conditioning process. The connection, Lashley reasoned, should have a definite locus in the brain just as a connection in a telephone system does; he, therefore, tried to find a definite localization of these connections. His basic technique was to train an animal to run a maze or make a discrimination both before and after he had made lesions of different sizes in various areas of the cerebral cortex. He then tested for such effects of the lesion as a deficit in retention or learning ability. Except for certain specific visual discriminations discussed below, he found no localization of function. Deficits were found, indeed, but they were not specific to any particular cortical areas. Instead, the degree of deficit depended on the amount of cortex removed rather than upon its locus.

W. S. Hunter and others argued that Lashley’s reasoning was faulty, and the present author agrees. Hunter pointed out that mazes involve many different cues, as others had shown by depriving animals of various senses, and complex motor responses. Quite specific localization of connections in the brain could well exist, but so many different connections would be involved in a habit like maze running that one could statistically expect the results Lashley obtained. Lashley’s experiments, therefore, were not crucial to the issue. But Lashley felt otherwise and believed that his experiments did disprove the existence of specific connections and required explanation in terms of field-theory concepts.

Thus, Lashley came to propose two concepts (or principles) for which he became widely known and which had considerable influence on subsequent research. The two concepts were mass action and equipotentiality. Both were presented in his 1929 monograph Brain Mechanisms and Intelligence. By mass action he referred to his finding that learning, or at least certain kinds of learning, is mediated by the cerebral cortex as a whole. This principle is based mainly on his studies of maze learning which showed that the efficiency of learning depends roughly on the amount of cortex present and not on any particular cortical locus.

The related concept of equipotentiality came out of his studies of vision and applies primarily to sensory systems. It refers to the ability of certain parts of a system to assume the functions of its other parts. Lashley had found, for example, that a rat can relearn a visual discrimination after the discrimination has been destroyed by a lesion of the visual cortex; also, a rat can discriminate visual stimuli perfectly when only a small remnant of its visual cortex remains intact. From such results he concluded that various parts of a system are “equipotential” for the mediation of a learned visual discrimination.

Other investigators have, of course, pursued the problems raised by Lashley’s work and his interpretations. Using more sophisticated physiological and behavioral techniques than Lashley had at his disposal and giving more attention to the brain of the primate, they have found more localization of function than the principle of mass action would lead one to expect. Indeed, in the primate brain there is considerable localization of learned functions. Still, Lashley was largely correct. The localization is far from precise, and within large areas of localized function there are mass-action effects. As for equipotentiality, later investigations bear out the presence of this phenomenon within sensory systems. It is the interpretation rather than the fact that is in question, and there are now complex alternative explanations available. The problem, however, remains far from solved and is in nearly the same state as Lashley left it.

Work on sensory functions

In another major phase of Lashley’s work, the study of sensory functions, he made considerable contributions to the study of the generalization of learned visual discriminations, much of the work being planned as tests of connectionist versus field theories. He also made contributions to neuroanatomy. Concentrating at first on the visual system, he traced neural connections between the retina and the lateral geniculate nucleus of the thalamus and between this nucleus and the cerebral cortex. Later he extended this kind of neuroanatomic analysis to other sensory systems. His papers on thalamocortical connections (1941) and on the microscopic structure of the cortex are classics in their fields. In them he showed that although there are point-to-point projections in sensory systems, these systems cannot be rigidly compartmentalized. Later work, with more refined techniques, has borne him out.

Work on neural functions

The final major aspect of Lashley’s work was an attempt to construct a general theory of neural function. Here he was frustrated; his grand design was to develop a theory of how the brain works in perception and learning. Having held earlier that other simple theories were untenable, he now turned to various forms of field theory. Many of his experiments and, particularly, his later papers were concerned with tests of such theories. In the end he felt he had succeeded only in exploding the theories proposed but not in devising one that would satisfactorily stand the test of experiment. He had to be content with the thought that he and his generation had only laid the groundwork for building a good theory at a later date. Despite his frustration in theory building, however, he adhered steadfastly to the belief that a satisfactory theory would some day be possible. In his last published article, “Cerebral Organization and Behavior,” he made an impressive case for his claim that the study of “the organization [of] mental states does not reveal any operations which cannot be accounted for in principle by the mechanism of the brain” (1958, p. 15).

Not long after this was written, Lashley collapsed and died in Poitiers, France. He left over 100 papers of an experimental or theoretical nature, but no book—because he could never make a large-scale theory stand up. Without question, he was the twentieth-century pioneer in the experimental study of brain functions and behavior.

Clifford T. Morgan

[For the historical antecedents of Lashley’s work, see the biographies ofBroca; Flourens; Gall. The relevant work of Lashley’s contemporaries is discussed in the biographies ofHunter; Meyer; Watson; Yerkes. For discussion of the development of Lashley’s ideas, seeNervous system; Psychology, article onPhysiological Psychology; Vision.]


1929 Brain Mechanisms and Intelligence: A Quantitative Study of Injuries to the Brain. Univ. of Chicago Press.

1930 Basic Neural Mechanisms in Behavior. Psychological Review 37:1–24.

1941 Thalamo-cortical Connections of the Rat’s Brain. Journal of Comparative Neurology 75:67–121.

1958 Cerebral Organization and Behavior. Pages 1–18 in Association for Research in Nervous and Mental Disease, The Brain and Human Behavior: Proceedings. Baltimore: Williams & Wilkins.

The Neuropsychology of Lashley: Selected Papers. Edited by Frank A. Beach et al. New York: McGraw-Hill, 1960. → A posthumous collection containing papers published between 1915 and 1958.


Beach, Frank A. 1961 Karl Spencer Lashley: June 7,1890–August 7, 1958. Volume 35, pages 163–204 in National Academy of Sciences, Biographical Memoirs. Washington: The Academy. → See pages 196–204 for a bibliography of Karl Lashley’s works.