Functional magnetic resonance imaging suggests patterns of blood flow associated with conscious and unconscious states.
Consciousness does not reside in a specific part of the brain. It arises from signals that are sent across the entire brain in a pattern that researchers are beginning to recognize. The ability to detect this pattern may help improve the diagnosis for people with brain damage. Currently, it is thought that approximately 40% of persistent vegetative state patients are misdiagnosed and are actually aware of their surroundings, even if they can’t talk or move in response to a doctor’s request.
In an attempt to address this issue, researchers used a functional magnetic resonance imaging scanner to track the blood flow in patients who were asked to imagine themselves hitting a tennis ball repeatedly. A 23-year-old woman who seemed to be unconscious was, based on the blood flow data, following the instructions in her mind.
This approach is still limited, however, because it requires that patients can still hear, which may not be the case if some gray matter is damaged. Researchers led by Enzo Tagliazucchi, a neuroscientist who studies wakefulness at the Brain and Spine Institute in Paris, then studied 125 people in the United States, France and Belgium, some healthy and some identified as having minimal or no signs of consciousness, examining their scan results for recurrent patterns of blood flow.
In the completely unresponsive patients, blood flowed from one connected region to another. In healthy patients, blood was more likely to move from one end of the brain to another. Next, they scanned anesthetized patients and obtained results similar to those for the unresponsive patients. In addition, those with covert consciousness exhibited the long-distance blood flows.
The researchers have more to consider. In some patients with damaged brains, both patterns were observed, suggesting there might be specific times when they could be reached. In some healthy patients, too, there were brief moments when the pattern indicating consciousness disappeared, leaving researchers to question what this change means.