Imagine lying inside a massive functional magnetic resonance imaging (fMRI) machine, your head surrounded by a 10-foot-wide white magnetic doughnut. While you lie there, daydreaming, the scientists in the room next door monitor the patterns of activity that flicker around in your brain.
Then someone sneaks up and stabs your hand with a fork. Nerve signals shoot up your spine, then radiate all over your brain: Ouch! The scientists in the next room didn’t see what happened. But since they’re looking at images of your brain on a monitor, it seems like there is no way they would miss what you just felt. Such an intense sensation must light up the fMRI scan like a Christmas tree, right?
Nope. In fact, your feeling of pain is impossible for them to decode, says Sean Mackey, a pain expert at Stanford’s Division of Pain Management. “Can you determine when another person is experiencing pain? No,” he says. “To date, nobody has ever done that.” This basic fact, that pain cannot be detected by anyone besides the person who is suffering, is a big reason why pain is so difficult to treat. Shockingly, there is still no way to measure pain beyond asking you how much it hurts.
