Why should a ghost disturb someone

Ghost experiences explained scientifically

Real illusion: What is behind “ghosts” or the feeling that an invisible presence is present? Researchers could now have found an explanation with the help of a “scientific necromancy”. Because their experiment shows that our brain reacts to contradicting information with an emergency solution: It changes body perception and creates the illusion of a ghostly presence, as the researchers report in the specialist magazine "Current Biology".

The delayed touch created the illusion of a ghostly presence © Blanke et al./ Current Biology

“It was as if someone invisible was still present…” - Some people have already experienced the feeling of a ghostly presence, many of them so real that they feel visited by a ghost. This is often dismissed as a mere hallucination or imagination, but there are reports of such experiences from almost all cultures. But what triggers this illusion of an invisible presence has so far remained unclear. Olaf Blanke from the Ecole Polytechnique Fédérale de Lausanne and his colleagues investigated this question with an experiment.

Robotic arm triggers ghostly apparition

For their study, the subjects were asked to control a robotic arm in front of them while they were blindfolded. The movements of this robot arm were digitally transferred to a second robot, which was positioned behind the standing test subjects and touched their backs. This contact gave the test subjects feedback on their actions: They felt on their backs how they were controlling the robotic arm in front of them. So far, so unspectacular.

But then the researchers changed the coupling of the two robotic arms so that the rear one reacted to the control with a time delay. And the ghosts promptly "appeared," as the researchers report. "30 percent of the participants spontaneously reported that they had the feeling that someone was behind them," says Blanke. Others had a kind of out-of-body awareness and felt that they were behind their own body. For some, these impressions were apparently so uncomfortable that they even stopped the experiment.

Invisible beings as an “emergency solution” for the brain

According to the researchers, these observations explain how the feeling of a ghostly presence can arise: Due to the time delay, the subjects' brains received contradicting signals from their own movement and tactile stimuli. The brain tries to resolve this contradiction by creating the illusory impression of another person. "This gave the participants the feeling that it was not they themselves who created this touch on their back with the robot arm, but someone else who was standing behind them," explains Blanke. For others, the perception of their own body changed so that they believed they were behind themselves.

In the opinion of the researchers, this emergency solution of the brain in the case of contradicting perceptions could also occur with other sensory stimuli - and thus form the basis for the feeling of ghostly presences. "Our data provide a scientific explanation for this phenomenon and combine this experience, which at first glance appears strange and complex, with the very fundamental integration of sensory and motor stimuli into our neural network," the scientists say.

Three areas of the brain involved

The observations can also explain why people with schizophrenia and patients who suffer from epilepsy, a brain tumor or other damage to the brain report particularly often such ghost experiences. When Blanke and his colleagues examined the brains of twelve such patients with ghost experiences in more detail, they found damage in three brain areas: the tempo-parietal cortex, the insula and, above all, the frontoparietal cortex.

All three are involved in the processing of spatial information and sensory stimuli. If they are damaged, then this can evidently lead to contradicting information in the brain even without a robotic arm or time delay or at least disrupt the processing of stimuli in such a way that we think we perceive ghostly phenomena. (Current Biology, 2014; doi: 10.1016 / j.cub.2014.09.049)

(Cell Press, 11/07/2014 - NPO)

November 7, 2014