TL;DR
Some patients who look completely unresponsive after a brain injury are aware, trapped behind a body that will not move. A Columbia University team has now shown that the ordinary scalp electrodes every intensive care unit already owns can find some of them: about one in three of 41 unresponsive patients changed the pitch of a tone just by imagining opening and closing their hands. A cheap bedside test could turn hidden awareness from something almost no hospital can check into something any ICU can screen for, and it might one day give those patients a way to answer simple questions. It is one small study, with no accuracy figures yet and no approval, but the equipment it needs is already at the bedside.
Below the line, for paid subscribers: The full story: where it stands, how we got here and what's dated next; our Odds board on 4 milestones, starting with "A larger validation trial of a bedside EEG test for hidden awareness reports results by 2028"; our labeled speculation on what it adds up to; and every source.