Much of what goes on in our brains happens without our awareness. The cells in our brain constantly exchange messages with various parts of our body through nerve cells called neurons, which pass on messages via electrical impulses. We see, hear, feel, taste, and are aware of our body sensations and position, not at the end of our nerves, but in our brains.

Sometimes it is difficult to know whether the signals are real or imaginary. In the strange effect of “phantom limbs,” people who have lost limbs can still experience a variety of sensations, like itching, in limbs that aren’t there.

Unfortunately, it is very common to feel quite severe pain in the missing limb. Amputees sometimes have the urge to reach for an object using a missing arm, or step out on a leg they don’t have. This effect is apparently related to an image of the body that persists in the brain. The sensations that are felt in phantom limbs arise from within the brain itself.

The brain’s neurons send out impulses that inform it about the body it controls. The brain learns to recognize the body’s pattern of signals or “neuron signature.” The sensations experienced in phantom limbs indicate that our neuron signature is pre-wired into the brain. Rather than just taking information from the real world, the brain sometimes generates its own messages which can disagree with known physical reality.

So next time you go to scratch your arm, it might be worth checking to see if it’s still there.