Stress and anxiety is known to impair cognitive function. In addition, in preclinical studies, the administration of distinct keystone bacterial strains improves cognitive function in an anxious mouse model. In humans, prebiotics and probiotics have been shown to ameliorate the stress response. In this aim the investigators seek to explore the association between prebiotics and perioperative cognitive outcomes in humans. The investigators will perform cognitive function testing using the same time-tested battery used in the department to study post-operative cognitive decline (POCD). Subjects will be tested for cognitive function preoperatively (T1) and at 1.5 months post-op (T4). The investigators hypothesize that patients receiving prebiotics during the perioperative period will show less post-operative cognitive dysfunction than controls.