Vegetative State and Minimally Conscious State

To date, VS and the MCS have both been defined by clinically observed behavioral responses. For example, VS is characterized by wakefulness in the absence of any awareness of self or environment. Typically, such a person retains autonomic functions with variable preservation of cranial and spinal reflexes but exhibits no clinical evidence of sustained, reproducible, purposeful, or voluntary behavioral responses to multisensory stimulation, nor evidence of language comprehension or response to command. MCS describes a spectrum of behavior that, at its most basic description, requires evidence of visual pursuit and, at best, involves intermittent responses to command. However, it has now become apparent using newer technologies, such as functional magnetic resonance imaging, that the distinction between VS and MCS cannot be based purely on observation. A notable proportion of patients considered to be in VS retain some awareness that is not consistent with their externally observable behavior.

The neuropathology of postanoxic VS and MCS is indistinguishable. There is characteristically little or no damage in the brainstem, but such patients commonly have evidence of diffuse necrosis in the cerebral cortex, variable abnormalities in the basal ganglia, and cerebellum, and severe thalamic damage. At a functional level, cerebral metabolic studies and magnetic resonance imaging have identified that the behavior during VS and MCS represents a functional disconnection syndrome in a large-scale frontoparietal network as a result of damage to long-range connectivity. The structures involved include the lateral and medial frontal regions, parietotemporal and posterior parietal areas, and posterior cingulate and precuneal cortex.

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