Brain scans may predict the possibility of someone recovering from a coma, a new study suggests.

Using a scanning technique called functional magnetic resonance imaging (fMRI), doctors have zeroed in on a poorly studied brain region called the posterior cingulate cortex (PCC) that appears to be involved with consciousness. Severe disruptions in this region — either as a result of head trauma or cardiac arrest — seem to squelch the possibility that the patient will ever regain consciousness, the researchers found.

The doctors compared brain scans of 27 people in a coma with 14 healthy people. All of the comatose people had significant disruption in the connections to and within the PCC. However, four of the coma patients recovered consciousness, and each of them still had brain activity between the PCC and a region called the medial prefrontal cortex. In fact, the neural activity between the two brain regions was the same for the healthy people and these patients who regained consciousness.

The observation suggests that fMRI scans of the PCC can help better inform doctors whether a coma patient might soon awaken or otherwise slip into a vegetative state, and the scans also may lead to better treatment options.

"We could be able to predict better who is more likely to recover from a coma," and eventually develop personalized treatments for people with brain injuries, said lead study author Dr. Stein Silva of INSERM U825, one of the French national research institutes in Toulouse. "The findings are promising, although more studies are needed on larger numbers of people to confirm the results, Silva said.

The study is published Wednesday in the journal Neurology. [Top 10 Mysteries of the Mind]

A coma is a prolonged period of unconsciousness in which a patient cannot be awakened, cannot open his or her eyes, and does not respond to stimuli such as pain, noise or light. All comas are temporary, however, usually lasting a few days to a few weeks. A patient either fully recovers or awakens with varying degrees of physical and cognitive impairment; transitions into a vegetative state with minimal or no awareness; or dies.

Doctors have been unable to predict which coma patients might awaken. Even the extent of a subsequent vegetative state is not predictive of recovery odds, because occasionally someone in a vegetative state for years might regain awareness.

(Some doctors now call this vegetative state "unresponsive wakefulness syndrome" because the patient may have sleep-wake cycles, with eyes opening and closing, yet still have no awareness of surroundings.)

Silva hypothesized that recovering consciousness after a coma depends on the extent of damage to brain connectivity to the PCC. He said that this particular brain region has been hard to image, and thus hasn't been studied as much as regions that are more accessible to brain scans.

Moreover, Silva said that research on brain function immediately after injury is lacking, despite the fact that there are more comatose patients than vegetative ones, and that there may be a greater chance for recovery if doctors learn how to repair damage soon after injury, before neural connections are completely lost.

Although the group's findings were striking — all four patients who awakened from their coma had brain scans clearly different from each of the 23 patients who did not awaken — Silva expressed caution in over-interpreting the results.

Aside from the small number of patients, which limits the statistical power of the results, Silva said there is a possibility that the fMRI findings could change depending on when the scan was performed after the coma-inducing injury. To this point, his research team hopes to perform earlier and repeated neuroimaging scans for a better understanding of the brain damage.

James Bernat, a coma expert and professor of neurology and medicine at the Dartmouth-Hitchcock Medical Center in New Hampshire, who was not part of the study, said the new study "adds one piece of a very large puzzle of how the brain regulates conscious awareness."

However, "we are a long way from confident prognosis of vegetative patients early in their course," Bernat told Live Science.

In 2013, a group of Italian researchers developed a type of "consciousness meter" in which they sent a magnetic pulse across the brain and measured the brain's response to it using electroencephalography (EEG). The technique could differentiate among various states of unconsciousness, such as REM sleep, deep sedation, coma or a vegetative state. This work is also ongoing.

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