Covert stroke occurs in one out of fourteen patients during or shortly after surgery, and may result in long-term disability. Fortunately, stroke that occurs during non-cardiac surgery is most commonly caused by inadequate blood flow to the brain and is, therefore, preventable if it can be detected early. Current clinical tools used to monitor the brain during surgery do not have the accuracy nor the spatial coverage - they only monitor one small region of the brain. In this study, the investigators plan to apply a cutting-edge optical device, tr-fNIRS, to monitor the whole brain during shoulder surgery. The primary aim is to determine any regional differences in cerebral oxygenation (ScO2) and cerebral autoregulation (CA)between brain regions during surgery and especially during various physiological challenges, such as hypotension. The investigators hypothesize that certain brain regions are more likely to develop cerebral desaturation and impaired CA, and are more prone to brain injury than the frontal lobe region which is the traditional monitoring site. The investigators also hypothesize that cerebral desaturation (or hypoxic injury) events correlate with adverse postoperative neurological outcomes such as covert stroke, overt stroke and/or postoperative delirium.