A. The Range of Consciousness


Consciousness in neurology and neuroscience is understood to have two different components:

1. Arousal (i.e., the level of consciousness): How aroused, alert, awake a person is?

2. Awareness (i.e., the content of consciousness): Is the person aware of what is around them and can respond?

B. Disorders of Consciousness

What kinds of disorders of consciousness arise if an individual has suffered an acute brain injury?

1. Coma: unconsciousness due to head trauma, disease, or stroke in which an individual cannot be awakened or brought to consciousness

2. Vegetative State (Unresponsive Wakefulness Syndrome): alternation between sleep and moderate arousal without awareness of surroundings. No clear sign of purposeful activity though there may be some cognitive activity. Some individuals do not progress beyond this state.

3. Minimally Conscious State: Brief periods of purposeful activity and some speech comprehension (but no speech production).

4. Locked-In Syndrome: Locked-in syndrome is a rare disorder of the nervous system. People with locked-in syndrome are:

• Paralyzed except for the muscles that control eye movement

• Conscious (aware) and can think and reason, but cannot move or speak; although they may be able to communicate with blinking eye movements

5. Brain Death

• no sign of brain activity and no response to stimuli (for 24 hours). These criteria include (1) a total unawareness to externally applied stimuli, (2) no movements or breathing, (3) no reflexes [e.g., pupils fixed and dilated], and a flat EEG. The tests for 1 through 4 must be repeated 24 hours later with no change.

• Originally proposed by the Ad Hoc Committee of the Harvard Medical School to Examine the Definition Brain Death in 1968

• The brain cannot itself sustain the body without significant life support. "The term brain death is defined as "irreversible unconsciousness with complete loss of brain function," including the brain stem, although the heartbeat may continue." (Encyclopedia of Death & Dying)

• Note, though, that there has been continuing controversy over these criteria.