In other words, when the going gets tough, we're not very good at determining whether someone is with us or not.
However, a new test, developed by Melanie Boly and her team at the University of Liège in Belgium, uses an electroencephalogram (EEG), to peer in at the brain, and the results suggest "that the key difference between minimally conscious and totally unconscious non-coma states is communication between the frontal cortex — the planning, thinking part of the brain — and the temporal cortex, where sounds and words are processed."
Boly and her colleagues...used EEG to measure electrical signals from the brains of 8 people in vegetative states, 13 in minimally conscious states and 22 healthy participants. The subjects were played a series of tones, which occasionally changed in pitch. The differing tone constituted a surprising event in the environment — something that the frontal cortex has to consider, so in all subjects the temporal cortex would send the frontal cortex a message.
In minimally conscious and healthy people the frontal cortex would then send a message back to the temporal cortex. The reason for this is uncertain; it may be to let the temporal cortex know what to expect in the future. But for people in a vegetative state, the communication was one-way: signals passed from the temporal to frontal area, but not back.
Interesting stuff. To read even more, see Test measures spark of consciousness