“The question we were trying to answer was can we use neuroimaging to objectively detect whether a person is in a state of pain or not. The answer was yes,” Dr. Sean Mackey of the Stanford University School of Medicine in California, whose study appears in the journal PLoS One.

Currently, doctors rely on patients to tell them whether or not they are in pain. And that is still the gold standard for assessing pain, Mackey said.

But some patients — the very young, the very old, dementia patients or those who are not conscious — cannot say if they are hurting, and that has led to a long search for some way to objectively measure pain.