Occlusion of the basilar artery may result in a "locked-in" syndrome, wherein the patient is completely quadriplegic and unable to speak. Infarction of the base of the pons interrupts the bilateral corticobulbar and corticospinal tracts, leaving the patient essentially disconnected from their body. Although such patients may be mistaken for being in a coma, they are actually awake and alert as the tegmentum is spared, the region where the ascending reticular activating system is located. Because control of vertical eye movements is located in the rostral midbrain, often the only voluntary movement is vertical gaze.