Copyright © 1999 Massachusetts Institute of Technology
Donald HEBB described Karl Lashley's career as "perhaps the most brilliant in the psychology of this century" (Hebb 1959: 142). Lashley's intellectual odyssey about brain and behavior extended from the earliest days of Watsonian BEHAVIORISM to astonishingly modern cognitive views.
Lashley attended the University of West Virginia, where he studied with John Black Johnston, a neurologist. When taking his first class from Johnston in zoology, Lashley "knew that I had found my life's work." Lashley plunged into the study of zoology, neuroanatomy, embryology, and animal behavior, graduating in 1910. He received an M.S. in bacteriology at the University of Pittsburgh in 1911, where he studied experimental psychology with K. M. Dallenbach. Following this he enrolled for the Ph.D. in zoology at Johns Hopkins with H. S. Jennings, with a minor in psychology with Adolf Meyer and John B. Watson. Watson's developing theory of behaviorism, and Watson himself, had a profound influence on Lashley.
In a letter written much later to Ernest Hilgard at Stanford, Lashley described taking a seminar with Watson in 1914. Watson called attention in the seminar to the writings of Bechterev and Pavlov on conditioned reflexes, which they translated.
In the spring I served as an unpaid assistant and we constructed apparatus and did experiments, repeating a number of their experiments. Our whole program was then disrupted by the move to the lab in Meyer's Clinic. There were no adequate animal quarters there. Watson started work with infants as the next best material available. I tagged along for awhile but disliked the babies and found me a rat lab in another building.
We accumulated a considerable amount of experimental material on the conditioned reflex that was never published. Watson sought the basis of a systemic psychology and was not greatly concerned with the reaction itself.
The conditioned reflex thus came to form the basis of Watson's behaviorism. Lashley, on the other hand, had become interested in the physiology of the reaction and the attempt to trace conditioned reflex paths through the central nervous system.
During the period at Hopkins, Lashley worked with Shepherd Irvory Franz at St. Elizabeth's Hospital in Washington. Together, they developed a new approach to the study of brain mechanisms of learning and memory and published landmark papers on the effect of cortical lesions on learning in rats. From this time (1916) until 1929, Lashley systematically used the lesion method in an attempt to localize memory traces in the brain. Following Watson (and Pavlov), Lashley conceived of the brain as a massive reflex switchboard, with sequential chaining of input-output circuitries via the cerebral cortex as the basis of memory. This work culminated in his classic 1929 monograph Brain Mechanisms of Intelligence. He was also president of the American Psychological Association that year. His presidential address, and his 1929 monograph, destroyed the switchboard reflexology theory of brain function and learning as it existed at that time. In complex mazes, rats were impaired in LEARNING and MEMORY in proportion to the degree of cerebral cortex destroyed, independent of locus. He employed the terms "mass action" and "equipotentiality" more to describe his results than as a major theory. Lashley did not deny localization of function in the neocortex. Rather, he argued that the neural substrate for higher-order memorial functions -- he often used the term "intelligence" -- as in complex maze learning in rats, was widely distributed in the CEREBRAL CORTEX.
Lashley was perhaps the most formidable critical thinker of his time, successfully demolishing all major theories of brain behavior, from Pavlov to the Gestalt psychologists to his own views. "He remarked that he had destroyed all theories of behavior, including his own" (Hebb 1959: 149). Near the end of his career, looking over his lifetime of research on memory, Lashley (1950) concluded that
This series of experiments has yielded a good bit of information about what and where the memory trace is not. It has discovered nothing directly of the real nature of the memory trace. I sometimes feel, in reviewing the evidence of the localization of the memory trace, that the necessary conclusion is that learning is just not possible. It is difficult to conceive of a mechanism that can satisfy the conditions set for it. Nevertheless, in spite of such evidence against it, learning sometimes does occur. (477-478).
Lashley's positive contributions were extraordinary. Perhaps most striking was his brilliant analysis of the "problem of serial order in behavior" (Lashley 1951). Ranging from the properties of language to the performance of complex motor sequences, he showed that "associative chaining" cannot account for serial behavior. Rather, higher-order representations must exist in the brain in the form of patterns of action "where spatial and temporal order are. . .interchangeable." (Lashley 1951: 128).
Lashley made a number of other major contributions, including an insightful analysis of "instinctive" behaviors, analysis of sexual behaviors, characterization of the patterns of thalamocortical projections, functions of the visual cortex, a rethinking of cortical cytoarchitectonics (Beach et al. 1960).
In 1936 James B. Conant, then the new president of Harvard, appointed an ad hoc committee to find "the best psychologist in the world" (Beach 1961). Lashley, then at the University of Chicago, was chosen and hired in 1937. He became director of the Yerkes Laboratory of Primate Biology in Florida but maintained his chair at Harvard, traveling to Cambridge once each year to give his two-week graduate seminar. The roster of eminent psychologists and neuroscientists who worked with Lashley is without parallel.
According to his student Roger SPERRY (personal communication), Lashley was interested in the problem of CONSCIOUSNESS but refused to write about it, considering it something of an epiphenomenon. He did, however, speculate about the mind, in itself heretical for a behaviorist:
"Mind is a complex organization, held together by interaction processes and by time scales of memory, centered about the body image. It has no distinguishing features other than its organization . . . there is no logical or empirical reason for denying the possibility that the correlation (between mental and neural activities) may eventually show a complete identity of the two organizations" (Lashley 1958: 542).
In his biographical memoir of Lashley, Frank Beach (1961) offered the following tribute (163):
Eminent psychologist with no earned degree in psychology
Famous theorist who specialized in disproving theories, including his own
Inspiring teacher who described all teaching as useless.
Beach, F. A. (1961). A biographical memoir [of Karl Lashley]. Biographical Memoirs of the National Academy of Sciences 35:162-204.
Beach, F. A., D. D. Hebb, C. T. Morgan, and H. W. Nissen, Eds. (1960). The Neuropsychology of Lashley. New York: McGraw-Hill.
Hebb, D. D. (1959). Karl Spencer Lashley, 1890-1958. The American Journal of Psychology 72:142-150.
Lashley, K. S. (1929). Brain Mechanisms and Intelligence. Chicago: University of Chicago Press.
Lashley, K. S. (1950). In search of the engram. Society of Experimental Biology, Symposium 4, pp. 454-482.
Lashley, K. S. (1951). The problem of serial order in behavior. In Cerebral Mechanisms in Behavior. New York: Wiley, pp. 112-136.
Lashley, K. S. (1958). Cerebral organization and behavior. Proceedings of the Association for Research in Nervous and Mental Diseases 36:1-18 .
Copyright © 1999 Massachusetts Institute of Technology