The clinical manifestation of coma is that the patient’s wakefulness-sleep cycle disappears and he/she is in a continuous “deep sleep” and cannot wake up. The patient’s perception, attention, thinking, emotion, orientation, judgment, memory and many other mental activities are all lost. The patient does not understand himself or the external environment and does not respond to external stimuli. The patient is unable to perform simple commands. When given a strong painful stimulus, there is no conscious response except for sometimes painful expressions or moans. 1. Atresia syndrome The atresia syndrome is also known as the loss of efferent state. The patient remains alert and aware of his situation, but the quadriplegia and cerebral nerve paralysis below the oculomotor nerve are caused by bilateral ventral lesions of the pons, involving the corticospinal tract, corticobulbar tract and corticomedullary tract. The patient is conscious, but can only indicate with vertical eye movements and blinking. Other causes include brainstem tumors and central pontine myelin lysis. Severe polyneuropathies, especially Guillain-Barré syndrome, myasthenia gravis and the use of neuromuscular junction blocking drugs can also cause a paralysis similar to that of atresia syndrome. 2. Persistent vegetative state Patients with persistent vegetative state lose cognitive neurological functions but retain autonomic functions such as cardiac activity, respiration and maintenance of blood pressure. This state occurs after coma and is characterized by a lack of awareness or cognitive deficits in the periphery, but maintains the sleep-wake cycle. Spontaneous movements may occur and the eyes may open in response to external stimuli, but there is no speech and no compliance with commands. Many syndromes that are not precisely defined are used as synonyms for persistent vegetative states, including alpha; coma, neocortical death, and persistent unconsciousness. These names lack precision and should be avoided whenever possible. The diagnosis of the syndrome should be made with caution and only after a long period of observation.