Researchers hope their work will help identify those who are actually conscious, but unable to communicate.
Their report appears in PLoS Computational Biology.
Awake but unaware
After catastrophic brain injuries, for example due to car crashes or major heart attacks, some people can appear to wake up yet do not respond to events around them.
Doctors describe these patients as being in a vegetative state.
Patients typically open their eyes and look around, but cannot react to commands or make any purposeful movements. Some people remain in this state for many years.
But a handful of recent studies have questioned this diagnosis - suggesting some patients may actually be aware of what is going on around them, but unable to communicate.
A team of scientists at Cambridge University studied 13 patients in vegetative states, mapping the electrical activity of their nerves using a mesh of electrodes applied to their scalps.
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