How the brain can feel a touch with no toucher
Touch normally begins when pressure or movement activates sensors in the skin. Those sensors send electrical signals through nerves to the spinal cord and brain, where the signals are interpreted as contact at a particular place. But a sensation does not require an object to press the skin: activity arising elsewhere along that pathway can sometimes produce a similar message.
Nerves and brain circuits are active even when no one is touching us. If they send signals that resemble incoming touch signals, the brain may interpret them as pressure, tingling, or a brief brush. The result can feel located on the shoulder or another specific spot, even though the skin there was not contacted.
When the signal and the skin no longer match
A well-known example is a phantom-limb sensation: after an amputation, some people still feel a limb that is no longer there. The brain’s networks for processing that limb do not simply vanish when it is removed, and activity in the remaining nerves and brain circuits can still be experienced as coming from it. That is one way the nervous system can generate a convincing sensation without contact at the apparent location.
The word hallucination can describe a perception without an outside stimulus; in this context, it does not by itself mean a person is imagining the sensation or experiencing a psychiatric disorder. The useful distinction is between the feeling and its cause: a touch can be real as an experience without being caused by anything touching the skin.
