Post-operative cognitive decline (POCD) has been detected in some studies in up to 50% patients undergoing major surgery. With an ageing population and an increasing number of elective surgeries, POCD may represent a major public health problem. However POCD research is complex and difficult to perform, and the current literature may not tell the full story. Dr Rob Sanders from the Wellcome Department of Imaging Neuroscience at UCL talks to us about the methodological limitations of previous studies and the important concept of a cognitive trajectory. In addition, Dr Sanders discusses the risk factors and role of inflammation in causing brain injury, and reveals the possibility that certain patients may in fact undergo post-operative cognitive improvement (POCI).