Studies show that 5 to 10% of people sometimes hear voices without having an underlying illness, for example the voices of deceased loved ones or a Supreme Being. This phenomenon therefore does not only affect people with a psychiatric illness, as is generally assumed.
But for the latter, hallucinations are a common disorder. “More than 70% of people with schizophrenia hear voices,” explains Pavo Orepic, a neuroscientist supported by the Swiss National Research Fund (SNSF). The most serious being that the words spoken are generally very negative. “Sometimes the voices repeat terrible things every day and thus persuade the people who hear them that they are worthless and that they must harm themselves.”
Angles of attack for treatment
In Olaf Blanke’s team at EPFL, Pavo Orepic developed a process that artificially causes the perception of voices and it is presented in the journal “Psychological Medicine”. Scientists can now study the occurrence of auditory hallucinations in healthy people and identify areas of attack for possible treatments. Indeed, even if the psychotropic drugs currently used partially relieve symptoms, they also have a non-specific effect on many body systems and cause severe side effects. By understanding the mechanisms at play behind auditory hallucinations, we could develop treatments with a specific effect.
“In fact, we have absolutely no idea what happens in the brain in the case of auditory hallucinations,” explains Pavo Orepic. Some studies suggest that they can occur when sensory impressions don’t match the brain’s expectations, such as when you put a cookie in your mouth that you think is sweet and turns out to be salty. Other studies have put forward an alternative explanation: hallucinations occur when the brain is already marked by previous impressions and then misinterprets the sensations.--
Pavo Orepic designed an experiment that triggers the following two mechanisms at the same time: the subjects, who are blindfolded, press a lever located in front of them while a robot that they do not see gives them a small blow in the back. As described in the first theory, the sensory impression therefore does not correspond to the brain’s expectations. Previous studies have established that over time, it gives subjects the illusion that they are touching their own backs.
Once people get used to the experience, the stroke is slightly delayed. “The brain must then find an explanation, such as the presence of another person,” explains Pavo Orepic. Such erroneous perception of a presence can lead to hallucinations according to the second theory. In order to see if this process promotes auditory hallucinations, the scientists then made the subjects listen to noises with very weak mixing of unknown voices, their own voices or no voices. People who were subjected to the robot experiment with the delayed tap more often heard unfamiliar voices in the noises they were made to listen to compared to the control conditions, even when no voices had been added. .
Predispositions present in everyone
“The result shows that the two theories regarding the occurrence of hallucinations are not mutually exclusive, but could be combined,” says Pavo Orepic. Furthermore, being able to study auditory hallucinations under controlled conditions in healthy people is a great advance. Indeed, in people who hear voices due to an illness, medications or other effects often interfere with the experiments, making it difficult to interpret the results. “Our study confirms that the mechanisms at play behind hallucinations are in fact present in all brains,” Pavo Orepic tells us. But for some reason, some people are more sensitive to it than others.”
Pavo Orepic believes that the line between harmless hallucinations and pathological hallucinations is also permeable. We can take as a criterion the negative influence that hearing voices can have on the lives of the people concerned (for example if it causes them to hurt themselves or prevents them from leading an independent life). But these voices can also be harmless, even positive, like when a deceased grandmother gives good advice.
Through his research, Pavo Orepic also hopes to contribute to destigmatizing people who hear voices. “To do this, we need to be able to know more about the causes of hallucinations and explain it to people.”