Geriatric patients have a high risk of developing postoperative cognitive deficits. Hypothetical causes are insufficient intraoperative cerebral perfusion or drugs that are administered in the perioperative setting. This study will investigate the role of these two factors in patients aged 65 or older undergoing elective surgical procedures under general aesthesia. Non-invasive techniques will be used to monitor intraoperative cerebral perfusion and anticholinergic activity in the patient's blood is determined. Data will be compared to those of a young (20-40 year old) group of patients undergoing elective surgical procedures using an identical anesthetic technique. A second control group of healthy volunteers older than 65 will be investigated to quantify practice effects with repeated testing of cognitive functions.