We hypothesize that this increased incidence is due to sub-cortical ischemia associated with the clamping of the ipsilateral carotid artery, because intra-operatively we rarely see EEG changes, or a significant number of emboli upon clamping or unclamping the carotid artery, or new cortical lesions of ischemia by MRI after surgery. In order to decrease cognitive dysfunction in patients with DM, we propose to randomize them to either i) have a shunt placed across the surgical site assuming it is surgically feasible or ii) be treated by "conventional" management during which time a shunt is placed only in the unlikely event of significant cortical ischemia determined by EEG, which occurs in about 5% of all cases.