In the first half of the 20th century, when the normal function of the corpus callosum was still a mystery, it was known that epileptic discharges often spread from one hemisphere to the other through the corpus callosum. This fact, along with the fact that cutting the corpus callosum had proven in numerous studies to have no obvious effect on performance outside the contrived conditions of Sperry s laboratory, led two neurosurgeons, Vogel and Bogen, to initiate a program of commissurotomy for the treatment of severe intractable cases of epilepsy despite the fact that a previous similar attempt had failed, presumably because of incomplete transections (Van Wagenen & Herren, 1940). The rationale underlying therapeutic commissurotomy which typically involves transecting the corpus callosum and leaving the smaller commissures intact was that the severity of the patients convulsions might be reduced if the discharges could be limited to the hemisphere of their origin. The therapeutic benefits of commissurotomy turned out to be even greater than anticipated: Despite the fact that commissurotomy is performed in only the most severe cases, many commissurotomized patients do not experience another major convulsion.