 In this study the investigator will randomize 273 subjects to deep 20C, low 20.1C-24C, or moderate 24.1C-28C hypothermia during aortic arch surgery with circulatory arrest. The primary purpose of this study is to determine the effect of deep vs low vs moderate hypothermia on neurocognitive function, brain functional connectivity, and leukocyte SUMOylation patterns after surgical circulatory arrest in participants. 