Karl Spencer Lashley (1890-1958) was an American psychologist and behaviorist. He is renowned for studying memory and learning. In 1920, he did a research to find an engram. An engram is a biological neural network where memory traces are stored.
As explained on page 342 of Gödel, Escher, Bach: An Eternal Golden Braid, he failed to find an engram in rats and thus concluded that it doesn't exist in any specific part of the brain and that memories aren't localized but are widely distributed across the cortex. By 1950, two theories have emerged from Lashley's research: mass action and equipotentiality. Mass action states that the rate, efficacy and accuracy of learning depend on the amount of cortex available. Equipotentiality states that if certain parts of the brain are damaged, other parts of the brain can take on the role of the damaged portion given that both portions are within the same functional area of the brain. Today we know that engrams do exist however their distribution is not equal across all cortical areas as Lashley thought. Certain types of knowledge are processed and contained in specific regions of the brain. Specialized circuits exist in every part of the brain and most brain tissue is highly specialized. One possible explanation for Lashley's failure to locate the engram is that his experiments were based on the complex task of maze running. In the processing of complex tasks, many types of memory (e.g. visual, spatial, smell, etc.) are used. Hence, many locations are involved in the complex task that eliminating one part of the brain is not enough to disrupt the entire task. The conclusion is that a typical cognitive act does activate many places in the brain, but each area is doing something different from the others: something for which it is specialized. Source: Karl Lashley. (n.d.). Retrieved December 17, 2014, from http://en.wikipedia.org/wiki/Karl_Lashley |