Karl Lashley and Wilder Penfield - Karl Lashley 1890-1958...

Karl Lashley
1890-1958
Karl Lashley & neuro-behaviorism (neurological bases of learning & behavior)
Student of JB Watson--assisted an ethological sea gull study with him
Wrote “Basic neural mechanisms in behavior” (1930) (1)
The principle of "mass action" stated that the cerebral cortex acts as one—as a whole—in
many types of learning.
The principle of " equipotentiality " stated that if certain parts of the brain are damaged,
other parts of the brain may take on the role of the damaged portion. (2) We also call this
phenomenon ‘brain plasticity’.
Describe the Karl Lashley Wilder Penfield debate.
Lashley advocated mass action of brain – EVIDENCE - after training rats in
a maze, Lashley could remove as much as 20% of rat brain and the rats
MEMORY of the learned maze remained intact. Lashley concluded that
memories were stored throughout brain (holograph analogy). Wilder
Penfield advocated memory localization of the brain EVIDENCE – ESB
prior to brain surgery – patients remained awake & conscious and when
Carl Lashley
(1)
(2)
(3)
(4)
%22the+behavioristic+interpretation+of+consciousness
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--- stimulated a specific region, the temporal lobe, a female patient reported
hearing a very specific melody, but only when Penfield electrically
stimulated one specific spot and no others (because the brain cortex lacks
sensation, the woman could not tell what point was being stimulated).
The notion that the brain, or at least the cerebral cortex, is uniform persisted well into the
twentieth century. In the 1920s, physiologist Karl Lashley trained rats to run mazes and
then systematically removed pieces of their brains in an effort to determine the location
of their maze-navigating memories. To his dismay, he found that the rats seemed simply
to do worse on the maze in proportion to the amount of brain removed, no matter where
the tissue was located. Lashley therefore proposed a “ law of mass action ”: that the
cortex is basically undifferentiated and participates in all thought equally. He felt that
removing pieces of rat cortex merely caused the rat to have less brain power. It is now
quite clear, however, that a more likely explanation for his findings is that the rats were
able to navigate the mazes by multiple means: the ones that had lost their sight could do it
using smell, for example, and vice versa.” (pg100-101)
Wilder Penfield
“It was the 1940s, and a patient lay on the operating table, fully conscious, with part of
her skull temporarily removed to expose the surface of her brain. Her surgeon at the
Montreal Neurological Institute, Dr. Wilder Penfield, delicately touched a small electrode
to her brain, and the patient announced that she had the sudden experience “of being in
her kitchen listening to the voice of her little boy who was playing outside in the yard.
She was aware of the neighborhood noises, such as passing motor cars, and understood
that might mean danger to him.” The patient suffered from epilepsy, the debilitating
affliction in which seizures, uncontrolled “storms” of electrical activity, begin in some