Corpus callosum
The thick bundle of nerve fibers that joins the right and left halves of the cerebrum. Surgeons began cutting it in 1940 to treat epilepsy, and in the 1960s researchers began testing the two halves of such patients separately.
An epileptic seizure grows as an electrical disturbance that starts in one place and spreads. In 1940 William Van Wagenen and R. Y. Herren in Rochester, New York, reported the results of cutting the corpus callosum in patients whose epilepsy did not respond to drugs[1]. Most of the twenty or so people operated on in the 1940s had only part of the corpus callosum cut; only one had both it and a second, smaller connection, the anterior commissure, cut completely[3].
Andrew Akelaitis, who examined the patients, concluded that their ability to recognize things by sight and touch, to carry out movements and to use language showed no obvious change[2]. Michael Gazzaniga later attributed this to tests that were not sensitive enough and to cuts that were incomplete in many patients[4].
In 1962 tests on W.J., whose corpus callosum and other connections had been cut completely, showed that a shape flashed briefly on one side of a screen stayed in one hemisphere, and that only the left hemisphere could answer in words[5].
Related terms
- Split brainA brain whose corpus callosum and other connections between the halves have been cut, so that the right and left halves work separately. Animal studies in the 1950s and patient studies from 1962 showed that what one half saw or learned, the other did not know.
- Optic chiasmThe place at the base of the brain where some of the fibers from each eye cross to the other side. In split-brain animal studies it was cut down the middle, so that what one eye saw reached only the hemisphere on the same side.
Sources
- W. P. Van Wagenen and R. Y. Herren, “Surgical division of commissural pathways in the corpus callosum: relation to spread of an epileptic attack,” Archives of Neurology and Psychiatry 44(4), 740–759 (1940).
- A. J. Akelaitis, “A study of gnosis, praxis and language following section of the corpus callosum and anterior commissure,” Journal of Neurosurgery 1(2), 94–102 (1944).
- J. E. Bogen, E. D. Fisher and P. J. Vogel, “Cerebral commissurotomy: a second case report,” JAMA 194(12), 1328–1329 (1965).
- M. S. Gazzaniga, “Forty-five years of split-brain research and still going strong,” Nature Reviews Neuroscience 6(8), 653–659 (2005).
- M. S. Gazzaniga, J. E. Bogen and R. W. Sperry, “Some functional effects of sectioning the cerebral commissures in man,” Proceedings of the National Academy of Sciences 48(10), 1765–1769 (1962).