A recent study using fMRI to attempt communication with severely brain-injured patients suggests that cognitive functioning may not be recognized at bedside. Patients have imagined activities like swimming to follow commands and answer questions.
Using a sophisticated imaging test to probe for higher-level cognitive functioning in severely brain-injured patients provides a window into consciousness. But the view it presents is one that is blurred in fascinating ways, say researchers at Weill Cornell Medical College of New York in the Feb. 25 online edition of the journal Brain.
In a novel study of six patients ranging in their function from minimally conscious state to the locked-in syndrome (normal cognitive function with severe motor impairment), the researchers looked at how the brains of these patients respond to a set of commands and questions while being scanned with functional magnetic resonance imaging (fMRI).
They found there was a wide, and largely unpredictable, variation in the ability of patients to respond to a simple command (such as “imagine swimming — now stop”) and then using that same command to answer simple yes/no or multiple-choice questions. This variation was apparent when compared with their ability to interact at the bedside using voice or gesture.
Some patients unable to communicate by gestures or voice were unable to do the mental tests, while others unable to communicate by gestures or voice were intermittently able to answer the researchers’ questions using mental imagery. And, intriguingly, some patients with the ability to communicate through gestures or voice were unable to do the mental tasks.
The researchers say these findings suggest that no exam yet exists that can accurately assess the higher-level functioning that may be, and certainly seems to be, occurring in a number of severely brain-injured patients — but that progress is being made.
“We have to abandon the idea that we can rely on a bedside exam in our assessment of some severe brain injuries. These results demonstrate that patients who show very limited responses at the bedside may have higher cognitive function revealed through fMRI,” says the study’s corresponding author, Dr. Nicholas D. Schiff, professor of neurology and neuroscience.
While progress has been made in elucidating the range of brain function in those who are severely injured, Dr. Schiff urges caution. “Although everyone wants to use a tool like this, fMRI is not yet capable of making clear measurements of cognitive performance. There will be a range of possible responses reflecting different capabilities in these patients that we have to further explore and understand,” he says.
The new study tested three levels of communication in steps that required increasing cognitive capacity, says Dr. Henning Voss, the study’s senior investigator. “While we could not unambiguously establish communication in these brain-injured patients, our research is helping us identifying problems specific to this patient population,” Dr. Voss says. “We got a clear picture about where and how to look for this kind of brain activity in response to certain commands.”
Read the full press release at newswise.com.
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