Neuroscientists awaken ghosts… hidden in our cortex
Generating a “ghost”
The researchers first analyzed the brains of 12 patients with neurological disorders – mostly epilepsy – who have experienced this kind of “apparition.” MRI analysis of the patients’s 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 one’s own body.
The scientists carried out a “dissonance” 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 participant’s brain is able to adapt and correct for it.
Next, the neuroscientists introduced a temporal delay between the participant’s movement and the robot’s touch. Under these asynchronous conditions, distorting temporal and spatial perception, the researchers were able to recreate the ghost illusion.
An “unbearable” experience
The participants were unaware of the experiment’s purpose. After about 3 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,” said 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,” explained Blanke. “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.”
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 body’s movements.
“Our brain possesses several representations of our body in space,” added Giulio Rognini. “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’.”
It is unlikely that these findings will stop anyone from believing in ghosts. However, for scientists, they only exist in our minds.
Anne-Muriel Brouet