Since the purpose of this study is to determine if a change in "conventional" management will improve patient's ability to perform our battery of neuropsychometric tests, we will randomly assign patients to either receive a "shunt" prophylactically if the surgeon determines that it is technically safe, even if conventional management does not indicate its necessary, or a "shunt" only if it is indicated by EEG, "conventional" management. Subjects in the prophylactic group will receive a shunt even when by standard criteria they would not need to receive one. Randomization will be performed in blocks of four patients each using a randomization table. Using "block" randomization we will increase the probability of an equal number of patients "shunted" or not shunted. The surgeon will be told which group the patient has been randomized into after induction and prior to clamping the carotid artery.