mar, 21 novembre 2023
Researchers can make people hear voices. A Swiss research team has developed a new method that triggers auditory hallucinations, as announced by the Swiss National Science Foundation (SNSF) on Monday. Their aim is to find new approaches for therapies.
The mechanism that causes people with mental illness in particular to hear voices is poorly understood, as the researchers from the Swiss Federal Institute of Technology in Lausanne (EPFL) and the University of Geneva wrote in the study published in the journal “Psychological Medicine”.
“We still have no idea what happens in the brain during auditory hallucinations,” clarified lead author Pavo Orepic in the SNSF press release. According to the brain researcher, more than seventy percent of people with schizophrenia hear voices. And what these voices say is usually negative.
In order to make non-hallucinating people hear non-existent voices, the researchers designed an experiment to confuse the brains of the study participants.
Earlier studies indicated that auditory hallucinations occur when sensory impressions do not match the brain’s expectations. Other studies explained vocal hallucinations by the fact that the brain interprets sensory perceptions incorrectly when it is shaped by previous impressions. In the experiment, the researchers combined these two theories.
In a first step, the blindfolded test subjects had to press a lever in front of them. At the same time, a robot that was not visible to them touched them on the back. According to the SNSF, this was aimed at the first theory, as the sensory impression of touching the back did not correspond to the brain’s expectations. Previous studies have already shown that the illusion that people are touching themselves on the back by pressing the lever is generated over time.
In the next step, this touch was delayed. The idea is that if the touch on the back is no longer synchronized with the pressing of the lever, the brain has to find a new explanation for this. For example, the presence of another person. According to the second theory, such a false perception of presence can promote hallucinations.
To test whether this experiment really triggered voice hallucinations, the researchers played noise sounds to the test subjects. In some cases, the noise was mixed with recordings of their own voice or other people’s voices, in others only the noise was heard.
It was found that after the experiment, people heard strange voices in the sounds more frequently, even if no voice was mixed in. The “hallucination engineering”, as it is referred to in the study, therefore worked.
According to the SNSF, the experiment shows that the two theories on the development of hallucinations may be intertwined. The study also confirms that the mechanisms behind hallucinations are actually present in every brain, said Orepic. “But for some reason, some are more susceptible to them than others.”
As the SNSF emphasizes in the press release, hearing voices does not necessarily mean that there is an illness behind it. Five to ten percent of all people sometimes hear voices, for example from a deceased grandmother giving advice. According to Orepic, the boundary between harmless and pathological hallucinations is fluid.
©Keystone/SDA
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