When people have a brain injury so severe that they canít squeeze a loved oneís hand or otherwise respond, there are few good ways to tell if they have any lingering awareness or are in a vegetative state. Now researchers have created a tool to peek inside the brain and measure varying levels of consciousness.
The work reported Wednesday is highly experimental, not ready for bedside use yet ó and if it pans out, a big question is how to use it without raising false hope. No one knows what level of consciousness at a certain point after injury really predicts recovery.
But it offers the hope that one day doctors might track consciousness nearly as easily as they check blood pressure.
ďConsciousness can grow and shrink,Ē said Dr. Marcello Massimini, a neurophysiologist at Italyís University of Milan who led the research to quantify just how much that is happening under different circumstances.
It seems obvious ó consciousness fades during deep sleep, and doctors can slip us under with anesthesia. Yet scientists donít have a good way to measure consciousness, especially when the very ill appear to be unconscious. Itís important to try to distinguish if patients are at least minimally conscious, and not in a vegetative state, because the sooner thereís some sign of awareness, the better the chance of recovery.
Today, doctors check if those patients can do things like blink or move a limb on command, or react to touch or pain. If not, scans of the brainís electrical activity may offer clues. Scientists even have put seemingly unconscious patients inside MRI scanners and told them to imagine throwing a ball. How the brain reacts can indicate if theyíre aware and just canít show it, whatís called locked-in syndrome. But all these tests have drawbacks.
The new work, reported in the journal Science Translational Medicine, aims for an easier, more objective measure. Itís based on the theory that consciousness depends on the complexity of activity in the brain, how well different regions connect and process information. For example, when youíre deeply asleep, the neighborís car alarm may not wake you but your brain still processes that you heard it. When youíre wide awake, it also processes how annoying the alarm is and how often it goes off.
Massiminiís team combined two well-known medical devices. First, a coil delivers a powerful pulse of magnetism that travels through the skull to stimulate the brain, essentially knocking on it to say ďwake up.Ē Then an EEG, which measures brain waves through electrodes attached to the scalp, records the patterns of activity as neurons fire in response.
The final trick: The researchers created a formula to compare the complexity of those resulting brain patterns by ďzippingĒ them, like digital files are compressed so they can be emailed. They called the resulting numerical measurement the PCI, or pertubational complexity index.
The team compared tests from 32 healthy people who were awake, asleep, dreaming or anesthetized, and 20 people with a variety of serious brain injuries. The two patients with locked-in syndrome clearly were aware, scoring nearly as high as awake and healthy people, they reported. The patients diagnosed as being in a vegetative state had scores as low as people rendered unconscious by the most powerful anesthesia. The minimally conscious were somewhere in-between.
The strategy could miss consciousness, so it wouldnít give doctors enough information for end-of-life decisions, researchers caution.
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