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Brain activity and diagnostic caution

Author: José Manuel Giménez Amaya
Published in: Blog A ciencia cierta
Publication date: February 2010

Neuroimaging techniques detect voluntary brain activity in some people in a vegetative state

The term "vegetative state" has been used to describe patients whose eyes open after a period of coma, but who are unable to make meaningful responses to various stimuli. It becomes "persistent" when patients remain in a "vegetative state" for more than 3 months after pathological processes that alter the oxygen supply to the brain, or more than 12 months after a head injury. The diagnosis of "minimally conscious state" is reservation for those patients who only respond in an erratic and limited manner to explorer commands or environmentally produced stimuli, but who can produce meaningful motor or verbal responses. In some patients in a persistent vegetative state, brain activity is detected when their name is called, but it is not clear what level of consciousness this reveals.

In an interesting study soon to be published in the New England Journal of Medicine, the authors detected voluntary activation of certain brain areas in 5 of 54 patients with complete unconscious states or minimal responses to stimuli. The brain activation occurred when the patients were given instructions to mentally move around their home or city or to imagine themselves playing tennis. The interesting thing about the experiment is that the brain areas activated were the same as those activated in healthy people. The study was carried out using modern neuroimaging techniques, in particular functional magnetic resonance imaging, which the same authors had previously used successfully to detect levels of consciousness in patients in a persistent vegetative state.

Although the frequency of brain activation in these pathological situations is not very high, the study makes it clear that in some cases it can occur. This underlines the importance of being cautious about the "apparent" complete lack of response in these patients. Furthermore, the data are significant enough to suggest that functional magnetic resonance imaging is a useful tool to classify and evaluate the prognosis of patients in coma states.