Karl Lashley
American psychologist and neuroscientist who searched for the brain's memory traces
American psychologist who removed parts of rats' cortex after maze training to look for where memories are stored. He concluded that memory is widely distributed, a view later research revised.
Why this person matters
Lashley's lesion studies shaped debate about whether learning is localised in the brain. His failure to find a single memory site is taught as a landmark negative result, even though later work showed that his assumption of an equal distribution across the cortex was wrong.
Main contributions
Lesion studies of maze learning
He trained rats on mazes and removed varying amounts of cortex, using surgical methods learned from Shepherd Ivory Franz and working alongside John B. Watson. The memoir reports that learning suffered roughly in proportion to the amount of cortex destroyed, but not with the location of the lesion.
Mass action and equipotentiality
In Brain Mechanisms and Intelligence (1929) he described mass action, learning mediated by the cortex acting as a whole, and equipotentiality, where parts of an area such as visual cortex can serve a discrimination equally. The memoir calls these summaries of findings, not explanations. He reviewed the search in 'In Search of the Engram' (1950).
Context and limits
Later research found that engrams are not spread equally across the cortex as Lashley assumed, and his conclusion about primary visual cortex is attributed to imperfect lesioning methods. Historian Nadine Weidman argues that a nativist, conservative racial ideology shaped his work; Donald Dewsbury disputes that reading and sees his views as more a matter of personality. The National Academy of Sciences memoir notes that he held no earned degree in psychology.
In your introductory course
Biological bases of behaviour.Appears in the biological bases chapter as the classic search for the engram and a reminder that memory is not stored in one place.
Related course reading: Psychology 2e, section 8.2. This is course context rather than a biographical source.
Years of active work
- 1914
Received his PhD from Johns Hopkins University with a thesis on inheritance in Hydra, having also studied under John B. Watson.
- 1929
Published Brain Mechanisms and Intelligence and became professor of psychology at the University of Chicago.
- 1935
Moved to a professorship in psychology at Harvard University.
- 1942
Became director of the Yerkes Laboratories of Primate Biology.
- 1950
Published 'In Search of the Engram'.
Sources
- National Academy of Sciences, Karl Spencer Lashley: A Biographical Memoir (Beach)Society or association. Institutional biography inspected.
- Encyclopedia.com, Lashley, Karl SpencerReference work. Reference article inspected.
- Cambridge University Press, Weidman, Constructing Scientific Psychology (book description)Publisher. Abstract inspected.
- Wikipedia, Karl LashleyReference work. Reference article inspected.