How long can blood flow to the brain be interrupted before death occurs?

Brain cells start to die if they go without oxygen for just 3-4 minutes and that's exactly what happens during a stroke.

Explanation:

Stroke is an abrupt interruption of constant blood flow to the brain that causes loss of neurological function. The interruption of blood flow can be caused by a blockage, leading to the more common ischemic stroke, or by bleeding in the brain, leading to the more deadly hemorrhagic stroke.

Brain death can occur rapidly as cells begin to die off without any oxygen stores or new oxygen circulating to the brain.