You Can Feel Pain in a Limb You No Longer Physically Have

Phantom pain affects a substantial share of people after limb amputation — even though the arm or leg is physically gone, the brain can still send signals that feel like real, sometimes very intense pain, localized exactly where the missing body part used to be.

This happens because the region of the cortex responsible for sensation from that limb doesn't disappear along with it — it stays active, and without its normal supply of incoming signals, it starts generating sensations on its own, often distorted and painful.

One method for easing the phenomenon is so-called mirror therapy: the patient watches the reflection of their healthy limb in a mirror positioned to visually "replace" the missing one — the brain can be fooled enough that the perceived pain genuinely decreases.

It shows just how much bodily sensation is, at bottom, a construction of the brain rather than a simple readout of signals from the body — the brain can "feel" a body part that's no longer physically there.