Strokes happen when blood flow to your brain stops. Within minutes, brain cells begin to die. There are two kinds of stroke. The more common kind, called ischemic stroke, is caused by a blood clot that blocks or plugs a blood vessel in the brain. The other kind, called hemorrhagic stroke, is caused by a blood vessel that definitionsbreaks and bleeds into the brain. “Mini-strokes” or transient ischemic attacks (TIAs), occur when the blood supply to the brain is briefly interrupted.

Traumatic brain injury (TBI) happens when a bump, blow, jolt, or other head injury causes damage to the brain. Every year, millions of people in the U.S. suffer brain injuries. More than half are bad enough that people must go to the hospital. The worst injuries can lead to permanent brain damage or death. Half of all TBIs are from motor vehicle accidents. Military personnel in combat zones are also at risk.

Symptoms of a TBI may not appear until days or weeks following the injury. A concussion is the mildest type. It can cause a headache or neck pain, nausea, ringing in the ears, dizziness, and tiredness.