Under normal circumstances the brain is able to form a unified self-perception, but lead researcher Olaf Blanke explained that when this malfunctions the brain creates a second representation of its body.

“Most of the research predicts that we cannot tickle ourselves because our brain precisely predicts of one hand, of my hand, touching my body or touching one or another position. However, if this is not fully integrated because I’m doing it or if I cannot correctly predict because somebody else were to touch me; in those cases of uncertainty, very often in those cases of double touch, the response is that you feel ticklish or tickled by somebody else,” said Blanke who is leading the research at the Swiss Federal Institute of Technology in Lausanne, Switzerland (EPFL).

Blanke’s team began by analyzing the brains of 12 patients with neurological disorders who have reported having such a secondary representation of their body, in other words a ghost sensation. MRI scans revealed abnormalities with three brain regions involved in self-awareness, movement and the sense of position in space. These brain regions together contribute to multi-sensory signal processing, important for the perception of one’s own body.