Recent publications show that using imagery instructions, brain activation patterns indicating consciousness can be found in approximately 10% of patients with unresponsive wakefulness syndrome (UWS; previously called vegetative state). It is possible, however, that patients who cannot follow instructions (because of limited memory/attention capacities, for example) are nevertheless conscious and retain emotional abilities to feel pain and pleasure. The aim of this study was to assess residual affective consciousness in a specific network of brain structures, the so-called pain matrix (PM) of the brain.
Methods:We examined 44 carefully diagnosed UWS patients at 2 imaging centers. fMRI was used to investigate the brain hemodynamic responses to (a) imagery instructions, and (b) pain cries as opposed to neutral human vocalizations.
Results:In line with the data of other groups, consistent responses to imagery instructions were obtained in 5 patients. In contrast, the PM was activated by pain cries in 24 patients. The PM consists of a sensory subsystem, which underlies pain sensation, and an affective subsystem, which underlies the characteristic aversive emotional tone of pain. The former was activated in 34% of patients, the latter in 30% of patients.
Conclusion:Although there is debate about whether patients with UWS can perceive their own pain, our data indicate that many of them respond to the signals of pain in others. One can speculate that "affective consciousness" can remain even in patients with very severe brain damage who have no capacity for cognition.
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