level of consciousness (LOC) [OFr, livel + L, conscire, to be aware of] , a degree of cognitive function involving arousal mechanisms of the reticular formation of the brain. The stages of response of the mind to stimuli vary from unconsciousness through vague awareness to full attention. The usual standard levels include coma, in which the patient does not appear to be aware of the environment; stupor, in which the patient is vaguely aware of the environment; drowsiness, in which the patient responds to stimuli but may be slow to react; and alert wakefulness. Impaired LOC may be expressed in obtundation or reduced alertness, stupor, syncope, or unresponsiveness. See also Glasgow Coma Scale, preconscious, subconscious.
