Postoperative delirium - a mental state of confusion, inattention, and impaired thought - is a potentially life-threatening condition. As many as half of patients that have heart and non heart-related surgery will experience postoperative delirium. Patients diagnosed with postoperative delirium have poorer outcomes and longer hospitalizations. Unfortunately, it is an under-diagnosed condition with a variable delay in when it appears. Additionally, there are no objective tools or tests that can be before or after surgery to anticipate and identify those patients who are at risk. Electroencephalography [EEG] and functional magnetic resonance imaging [fMRI] have helped us understand the changes in the brain during delirium. These suggest that a weakening in correlated activity within a group of brain regions, known as the default mode network (DMN), may be related to delirium.