Mini-strokes, or transient ischemic attacks (TIAs), are caused by a temporary disruption of the blood supply to the brain. Causes can include a blood clot in an artery, a blocked artery, an artery spasm, or plaque buildup within the artery. In older people, the most common cause of mini-strokes is narrowing of the arteries due to atherosclerosis or hardening of the arteries.