The default network in the brain may be responsible for daydreaming
Researchers may have found a way to predict whether severely brain-damaged patients will regain consciousness.
A part of the brain which can stay active even in severely brain-damaged patients could offer a clue about the chances of recovery, they claim.
The Belgian team told a conference that activity within a "default network" in the brain appears to match the level of consciousness of the patient.
Some believe the default network is associated with daydreaming.
The findings were reported in New Scientist magazine.
The default network in the brain's cortex appears to be more active when the brain is not actively working on a goal - hence the proposed link with daydreaming.
Some evidence suggests that it helps get the brain ready for the next task, although this remains a controversial theory.
A number of techniques are used to assess the level of consciousness in people following head injury, and while some are diagnosed as "brain dead", with no sign of any activity in the brain, it can be difficult to make an exact diagnosis when the patient has a higher level of activity, but is still unconscious.
Dr Steven Laureys, from the University of Liege in Belgium, believes that activity within the network could help confirm the level of consciousness, and help doctors decide on whether or not to treat them.
He measured activity in 13 brain-injured patients with a variety of different levels of consciousness.
Some were "minimally conscious", while others were in a coma, or a persistent vegetative state (PVS). A final group were "brain dead".
He found that minimally conscious patients had only a 10% fall in normal activity in this area, while in coma and PVS patients, it fell by approximately 35%.
There was no activity at all in the brain-dead patients.
Dr Laureys told New Scientist this could be more reliable method of assessing patients: "We could just scan someone for 10 minutes and get an easily quantifiable readout."
Dr Jon Simons, a neuroscientist from Cambridge University, said that the study, although preliminary, was "very interesting".
"It suggests that connectivity in the default network might correlate with level of consciousness as measured by a coma-recovery scale.
"Although the functional significance of the default network is still being hotly debated, this study does suggest that scans of the default network might perhaps have clinical utility as a diagnostic tool."