Monday, February 20, 2012
The term coma describes a severe decrease in mental function due to structural, physiological, or metabolic impairment of the brain. A person in a coma exhibits a sustained loss of the capacity for arousal even in response to vigorous stimulation. There is no outward behavioral expression of any mental function, the eyes are closed, and sleep–wake cycles disappear. Coma can result from extensive damage to the cerebral cortex, damage to the brainstem arousal mechanisms, interruptions of the connections between the brainstem and cortical areas, metabolic dysfunctions, brain infections, or an overdose of certain drugs, such as sedatives, sleeping pills, or narcotics. Patients in an irreversible coma often enter a persistent vegetative state in which sleep–wake cycles are present even though the patient is unaware of his surroundings. Individuals in a persistent vegetative state may smile, or cry, or seem to react to elements of their environment. However, they have no comprehension of these behaviors.