What happens when the arteries to the brain are blocked?

The brain requires oxygen to generate the energy it needs to operate. Blood provides the necessary oxygen transport. Blocking the arteries would starve the brain of oxygen and the brain would rapidly start shutting down. Starve it of oxygen long enough (about one minute) and cells stop functioning properly and even start dying, escalating rapidly to whole brain death.

This is not a healthy thing to do. Do not try this at home.