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Consciousness ˈkän-chə-snəs

By Kenneth Maiese, MD, Member and Advisor, Biotechnology and Venture Capital Development, Office of Translational Alliances and Coordination; Past Professor, Chair, and Chief of Service, Department of Neurology and Neurosciences, National Heart, Lung, and Blood Institute; Rutgers University

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. Affected people usually appear sluggish, drowsy, unconscious, or asleep. They may be difficult to arouse, as occurs in stupor, or impossible to arouse, as occurs in coma. 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.

Often, disorders that impair wakefulness also impair mental function, as occurs in delirium.