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Unconscious Brain Still Registers Pain

9 October 2008 (All day)
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Reuters

Altered perceptions? Minimally conscious patients may have a greater capacity to feel pain than do those in a vegetative state (such as Terri Schiavo, above).

Most of the time, doctors have a simple way to determine if a patient needs pain medication: They ask. But when a brain injury renders someone unable to respond to questions, the right course of action becomes murkier. Now a study finds that the brains of some patients with brain injuries respond to an unpleasant electrical shock much as do the brains of healthy people, suggesting that these patients may feel pain even though they're unable to show it.

Little is known about pain perception in unconscious patients, says Steven Laureys, a neurologist at the University of Liège in Belgium and the senior author of the new study. As a result, whether to provide drugs is up to individual doctors. Some doctors withhold medications, Laureys says, assuming that these patients are unable to feel pain. Other doctors give drugs more liberally but in turn risk sedating patients and missing flickering signs of consciousness.

In the new study, Laureys and colleagues used positron emission tomography (PET) to measure activity in the brains of 15 healthy volunteers; 15 patients in a "vegetative state," a condition famously exemplified by Terri Schiavo, who showed signs of wakefulness but was unresponsive and unaware of her surroundings; and five patients in a somewhat better condition known as a "minimally conscious state," characterized by limited and sporadic responsiveness and awareness. Whereas minimally conscious patients may occasionally look toward someone who calls their name, for example, vegetative patients cannot respond.

In healthy subjects, a zap to the wrist elicited activity in brain regions that rev up in response to pain, including the thalamus, insula, somatosensory cortex, and anterior cingulate cortex. In patients who were in a vegetative state, activity in these regions was reduced, and the timing of firing across different regions was abnormal. But the minimally conscious patients exhibited levels and timing of brain activity that were very similar to those in healthy people, the researchers report online this week in The Lancet Neurology. Although PET scans and other neuroimaging tools won't ever reveal what people actually feel, Laureys says the new findings suggest that minimally conscious patients may have a greater capacity to register pain compared with those in a vegetative state--and a greater need for drugs to treat it. The capacity to feel pain may be another factor for patients' families to consider when weighing end-of-life decisions, he adds.

The findings are an important contribution to an understudied area, says Nicholas Schiff, a neurologist at New York-Presbyterian Hospital/Weill Cornell Medical College in New York City. Minimally conscious patients can't talk or even wince to let doctors know they're in pain, Schiff notes: "There's nothing to guide you without this kind of data." Even so, Schiff says, researchers need to study a larger sample of patients before making specific guidelines for pain medications.

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