Lashley, Karl (1890-1958)
LASHLEY, KARL (1890-1958)
Karl Spencer Lashley pioneered the study of brain mechanisms of learning and memory. He was born in 1890 in Davis, West Virginia, and entered the University of West Virginia at the age of fifteen. As a freshman he signed up for a class in zoology under the distinguished neurologist John Black Johnston, and within a few weeks he "knew that I had found my life work." After graduation in 1910, he obtained a teaching fellowship at the University of Pittsburgh and received his M.S. degree there. Lashley then went to Johns Hopkins University to study for his doctorate in zoology under Herbert S. Jennings. He elected a minor in psychology with John B. Watson, the founder of behaviorism. His work with Watson convinced him to make his career in psychology. This was the critical time in Lashley's development as a scientist. In his own words:
In 1914, John Watson called attention to a seminar in the French edition of Bechterev's book on the conditioned reflex. In that winter the seminar was devoted to the translation and discussion of the book. In the spring I served as an unpaid assistant and we constructed apparatus and did experiments, repeating a number of Pavlov's 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 systematic psychology and was not greatly concerned with the reaction itself (letter from K. S. Lashley to Ernest Hilgard, ca. 1930; reprinted with the permission of Professor Hilgard).
The conditioned reflex formed the basis of Watson's behaviorism. Lashley, on the other hand, became interested in the physiology of the reaction and the attempt to trace conditioned reflex paths through the central nervous system. Over the next several years Lashley collaborated with Shepherd Franz, who was then at St. Elizabeth's Hospital in Washington, DC. Their research, examining effects of lesions of the frontal cortex on learning abilities in the rat, was the foundation of his major work, Brain Mechanisms and Intelligence (1929). In 1920 Lashley accepted an assistant professorship at the University of Minnesota and began in earnest his search for the memory trace. He was made full professor at Minnesota in 1924, and in 1926 moved to the University of Chicago, where he became a professor in 1929. In this same year he was president of the American Psychological Association and published his monograph Brain Mechanisms and Intelligence. In 1935 Lashley accepted a professorship at Harvard University, and in 1937 he was appointed research professor of neuropsychology with nominal teaching duties, which made it possible for him to accept the directorship of the Yerkes Laboratories of Primate Biology in Orange Park, Florida, in 1942. He held both these positions, spending only a few weeks a year at Harvard (he was not fond of formal teaching), until his death in 1958.
Lashley devoted many years to an analysis of brain mechanisms of learning, using the lesion-behavior method that he developed and elaborated from the work with Franz. During this period, Lashley's theoretical view of learning was heavily influenced by two widely held notions: localization of function in neurology and behaviorism in psychology.
Localization of function, the notion that each psychological "trait" or function has a specific locus of representation, a particular place, in the brain, was perhaps the major intellectual issue concerning brain organization at the beginning of the twentieth century. An extreme form of the idea of localization, known as phrenology, was popular early in the nineteenth century. The field of neurology then moved away from that position, though the discovery of a speech center began to move the pendulum back. Work in the last three decades of the nineteenth century identified the general locations of the motor, visual, and auditory regions of the cerebral cortex. Localization of function appeared to be winning the day.
In Watson's behaviorism, the learning of a particular response was held to involve the formation of a particular set of connections, a series set. Consequently, Lashley argued, it should be possible to localize the place in the cerebral cortex where that learned change in brain organization, the engram (memory trace), was stored. It was generally believed at the time, consistent with Ivan Pavlov's view, that learning was coded in the cerebral cortex. Thus, behaviorism and localization of function were consistent; they supported the notion of an elaborate and complex switchboard on which specific and localized changes occurred in the cerebral cortex when specific habits were learned.
Lashley systematically set about finding the places in the cerebral cortex where learning occurred—the engrams—in an extensive series of studies culminating in his 1929 monograph. In this research he used mazes of differing difficulty and made lesions of varying sizes in different regions of the cerebral cortex of the rat. The results profoundly altered Lashley's view of brain organization and had an extraordinary impact on the young field of physiological psychology: the locus of the lesion was unimportant; the size was critically important, particularly for the difficult mazes. These findings led to Lashley's notions of equipotentiality (locus not important) and mass action (size critical).
Subsequently, Lashley focused on a detailed analysis of the role of the cerebral cortex in vision and in visual discrimination learning and memory. But his interests and research also included classic work on the cytoarchitectonics (microscopic structure) of the cerebral cortex; a brilliant analysis of the problem of serial order in human language and thought; and a penetrating analysis of the biological substrates of motivation. Lashley, more than any other scientist, shaped and developed the field of physiological psychology.
It is fitting to close this biographical entry with Lashley's own summing up of his search for the memory trace, written in 1950:
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.
See also:LOCALIZATION OF MEMORY TRACES
Lashley, K. S. (1929). Brain mechanisms and intelligence: A quantitative study of injuries to the brain. Chicago: University of Chicago Press.
—— (1935). The mechanism of vision, Part 12: Nervous structures concerned in the acquisition and retention of habits based on reactions to light. Comparative Psychology Monographs 11, 43-79.
—— (1950). In search of the engram. Society of Experimental Biology, Symposium 4, 454-482.
Orbach, J., ed. (1982). Neuropsychology after Lashley. Hillsdale, NJ: Erlbaum.