A temporary decrease in the blood supply to some part of the brain. The affected part of the brain does not function properly, producing the symptoms observed. The syndrome looks similar to a stroke except the symptoms resolve quickly, usually within an hour. The most common causes of TIA are atherosclerosis and atrial fibrillation. These patients need a prompt work-up to identify and treat the cause of the TIA because of the high risk of stroke, especially within the first week after a TIA.