Merck Manual

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Consciousness

By

Kenneth Maiese

, MD, Rutgers University

Last full review/revision May 2022
CLICK HERE FOR THE PROFESSIONAL VERSION

Consciousness has two parts:

  • Whether a person is awake and alert (wakefulness)

  • What people are conscious of (content)

When wakefulness (alertness) is impaired, people do not respond normally to the outside world (for example, when they are touched or spoken to), and they do not acquire information from it. If wakefulness is impaired, people usually appear sluggish, drowsy, unconscious, or asleep. They may be difficult to arouse, as occurs in stupor Stupor and Coma Stupor is unresponsiveness from which a person can be aroused only by vigorous, physical stimulation. Coma is unresponsiveness from which a person cannot be aroused and in which the person's... read more , or impossible to arouse, as occurs in coma Stupor and Coma Stupor is unresponsiveness from which a person can be aroused only by vigorous, physical stimulation. Coma is unresponsiveness from which a person cannot be aroused and in which the person's... read more . Impaired wakefulness is often called impaired consciousness.

The content of consciousness depends on mental (cognitive) function and involves understanding and processing what is experienced and encountered. When mental function is impaired, people have problems with memory, thinking, judgment, and learning, as occurs in dementia Dementia Dementia is a slow, progressive decline in mental function including memory, thinking, judgment, and the ability to learn. Typically, symptoms include memory loss, problems using language and... read more .

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