Using a robot to trigger the frightening feeling of a ‘phantom presence’, neuroscientists show that ghosts only exist in our minds. The results shed light on brain signals involved in self-awareness as well as disorders such as schizophrenia.
On June 29, 1970, the legendary mountaineer Reinhold Messner had a strange experience. “Suddenly there was a third climber with us, (…) a little to my right, a few steps behind me, just outside my field of vision,” he said later, recounting his descent down the virgin summit of Nanga Parbat with his brother – freezing, exhausted and oxygen-starved in the vast barren landscape. Stories of such ‘supernatural’ experiences have been reported countless times by mountaineers, explorers and survivors, by people who have been widowed, as well as by patients suffering from neurological or psychiatric disorders. They commonly describe a presence that is felt but not seen, akin to a guardian angel or a demon, inexplicable, illusory and persistent.
A research team at École Polytechnique Fédérale de Lausanne’s (EPFL) has now unveiled these ‘ghosts’. In the laboratory of Professor Olaf Blanke, neuroscientists were able to recreate the illusion of ‘a presence’ and provide a simple explanation for it. They showed that the feeling actually results from an alteration of ‘sensorimotor’ brain signals, which are involved in generating self-awareness by integrating information from our movements and our body’s position in space.
As reported in the journal Current Biology, Blanke’s team interfered with the sensorimotor input of participants so that their brains no longer identified such signals as belonging to their own body, but instead interpreted them as those of someone else.
Creating a ‘ghost’
The researchers first analysed the brains of 12 patients with neurological disorders – mostly epilepsy – who have experienced this kind of ‘apparition’. Magnetic resonance imaging (MRI) analysis of the patients’ 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. Together, they contribute to multisensory signal processing, which is important for the perception of one’s own body.
The scientists carried out a ‘dissonance’ experiment. Blindfolded participants were asked to do movements with their hand in front of their body. Behind them, a custom-designed robot reproduced their movements, touching them on the back in real time. This gave a kind of spatial discrepancy, but because of the synchronised movement of the robot, the participant’s brain was able to adapt and correct for it.
Next, the neuroscientists introduced a delay between the participant’s movement and the robot’s touch. Under these asynchronous conditions, distorting the perception of time and space, the researchers were able to recreate the ghost illusion.
An ‘unbearable’ experience
The participants were unaware of the experiment’s purpose. After about three minutes of the delayed touching, the researchers asked them what they felt. Instinctively, several subjects reported a strong ‘feeling of a presence’, even counting up to four ‘ghosts’ where none existed. “For some, the feeling was even so strong that they asked to stop the experiment,” says Giulio Rognini, who led the study.
“Our 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,” Blanke explains. “The 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.”
Towards a deeper understanding of schizophrenia
In addition to explaining a phenomenon that is common to many cultures, the aim of the 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 body’s movements.
See the research explained in a video featuring Olaf Blanke, Director of the Center for Neuroprosthetics, Bertarelli Chair in Cognitive Neuroprosthetics at EPFL and Professor at the University Hospital of Geneva.
The research was conducted in close collaboration with Professor Hannes Bleuler of EPFL’s Laboratory of Robotic Systems, and supported by the National Center for Competence in Research – Synapsy.
“Our brain possesses several representations of our body in space,” Rognini says. “Under 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 – or, in this case, a robot – this can sometimes create a second representation of one’s own body, which is no longer perceived as ‘me’ but as someone else, a ‘presence’.”
Will these results stop anyone from believing in ghosts? Probably not. But for scientists, at least, ghosts only exist in our minds.
– Adapted from EPFL Mediacom