Insufficient blood supply to the anterior and posterior systems of the brain causes different early symptoms, as follows: 1. Anterior system: i.e., the internal carotid artery system, which usually causes dizziness, drowsiness, and even drowsiness and memory loss; 2. Posterior system: i.e., the vertebrobasilar artery system, which is usually dominated by dizziness and causes a series of symptoms in severe cases, such as weakness of limbs, cold sweats, and even numbness of limbs, paralysis, coma, and impaired consciousness. Because the posterior circulation innervates the cerebellum and brainstem, which have vital center, respiratory center, heartbeat center, etc., more serious symptoms may occur if the blood supply is insufficient.