How can a scanner find a response in someone who shows none at the bedside? · Lobeworks/17

By asking for an answer that needs no movement.

How can a scanner find a response in someone who shows none at the bedside?

By asking for an answer that needs no movement. The person is told, at set times, to imagine a movement and then to rest, and fMRI looks for activity that rises and falls with the instructions and with nothing else. A response that follows the commands shows the person heard and acted on them, even though no muscle moved. The test only works in one direction: a response is evidence, and its absence is not, since it misses many people who can follow commands visibly.