Disorders of Consciousness

At the extreme of disorders of alertness are the so-called disorders of consciousness, including coma, persistent vegetative states, and hyperkinetic or akinetic mutism. In the case of coma, the patient cannot be aroused and is unresponsive to internal and external stimuli. In contrast, the persistent vegetative state is differentiated from coma by the presence of cyclic arousal (resembling sleep-wake cycles) but without cognitive alertness or responsivity. Both coma and persistent vegetative state are associated with damage in the brain stem and both conditions are described as deficits of alertness.

In akinetic and hyperkinetic mutism, the deficit is less obviously one of alertness, although patients with either condition are unresponsive and apparently unconscious. Akinetic mutism resembles the persistent vegetative state in that the patient is unresponsive but shows spontaneous eye opening and may show smooth pursuit tracking of visual stimuli. This state has been described as "hypervigilant": The patient appears to be alert and attentive although he or she remains unresponsive. This disorder results from damage to frontal cortical and subcortical areas, such as that which occurs following rupture of the anterior communicating artery. The converse condition appears to be hyperkinetic mutism, in which the patient displays coordinated motor activity but without attention and apparent awareness. Hyperki-netic mutism is seen following damage to posterior attentional circuits of the parietal and occipital lobe, leaving frontal cortex intact. In both cases, the brain stem activating systems are intact: The forebrain executive systems are compromised. Thus, these conditions might represent the dissociation of consciousness (which is impaired) and alertness (which is present).

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