Neuroscientists awaken ghosts⊠hidden in our cortex
On June 29, 1970, mountaineer Reinhold Messner is about to live an unusual experience. Recounting his descent down the virgin summit of Nanga Parbat with his brother, freezing, exhausted and oxygen-starved in the vast barren landscape, he says: âSuddenly there was a third climber with us, (âŠ) a little to my right, a few steps behind me, just outside my field of vision.â It was invisible, but there. Stories like this have been reported countless times by mountaineers, explorers and survivors, as well as by people who have been widowed, but also by patients suffering from neurological or psychiatric disorders. They commonly describe a presence that is felt but unseen, akin to a guardian angel or a demon, inexplicable, illusory and persistant.
Olaf Blankeâs research team at EPFL has now unveiled the ghost. They were able to recreate the illusion of a presence in the laboratory, and provided a simple explanation. They showed that the âfeeling of a presenceâ actually results from an alteration of âsensorimotorâ brain signals, which are involved in generating self-awareness by integrating information from our movements and our bodyâs position in space. In their experiment, Blankeâs team interfered with the sensorimotor input of participants in such a way that their brains no longer identified such signals as belonging to their own body, but instead interpreted them as those of someone else. The work is published in Current Biology.
Generating a âghostâ The researchers first analyzed the brains of 12 patients with neurological disorders â mostly epilepsy â who have experienced this kind of âapparition.â MRI analysis of the patientsâs brains revealed interference with three cortical regions: the insular cortex, parietal-frontal cortex, and the temporo-parietal cortex. These three areas are involved in self-awareness, movement and the sense of position in space (proprioception). Together, they contribute to multisensory signal processing, which is important for the perception of oneâs own body.
The scientists carried out a âdissonanceâ experiment. Blindfolded participants performed movements with their hand in front of their body. Behind them, a robotic device reproduces their movements, touching them on the back in real time. The result is a kind of spatial discrepancy, but because of the synchronized movement of the robot, the participantâs brain is able to adapt and correct for it.
Next, the neuroscientists introduced a temporal delay between the participantâs movement and the robotâs touch. Under these asynchronous conditions, distorting temporal and spatial perception, the researchers were able to recreate the ghost illusion.
An âunbearableâ experience The participants were unaware of the experimentâs purpose. After about 3 minutes of the delayed touching, the researchers asked them what they felt. Instinctively, several subjects reported a strong âfeeling of a presenceâ, even counting up to four âghostsâ where none existed. âFor some, the feeling was even so strong that they asked to stop the experiment,â said Giulio Rognini, who led the study.
âOur experiment induced the sensation of a foreign presence in the laboratory for the first time. It shows that it can arise under normal conditions, simply through conflicting sensory-motor signals,â explained Blanke. âThe robotic system mimics the sensations of some patients with mental disorders or of healthy individuals under extreme circumstances. This confirms that it is caused by an altered perception of their own bodies in the brain.â
A deeper understanding of schizophrenia In addition to explaining a phenomenon that is common to many cultures, the aim of this research is to better understand some of the symptoms of patients suffering from schizophrenia. Such patients often suffer from hallucinations or delusions associated with the presence of an alien entity whose voice they may hear or whose actions they may feel. Many scientists attribute these perceptions to a malfunction of brain circuits that integrate sensory information in relation to our bodyâs movements.
âOur brain possesses several representations of our body in space,â added Giulio Rognini. âUnder normal conditions, it is able to assemble a unified self-perception of the self from these representations. But when the system malfunctions because of disease â or, in this case, a robot â this can sometimes create a second representation of oneâs own body, which is no longer perceived as âmeâ but as someone else, a âpresenceâ.â
It is unlikely that these findings will stop anyone from believing in ghosts. However, for scientists, they only exist in our minds.
