A new study by scientists proves that a person does not experience hallucinations for the reason that his brain constantly doubts its beliefs and expectations and checks with reality.
When this permanent activity is disturbed, hallucinations occur. According to the authors of the study, representatives of Yale University, thanks to this discovery, scientists will be able to develop more effective remedies against mental disorders and diseases, in particular, schizophrenia.
A person does not always perceive the world as he hears and sees: in most cases he trusts his own expectations so much that the brain, even in the absence of stimuli, begins to produce them itself. Thus, hallucinations may be the result of an over-obsession with expectations instead of referring to auditory (sensory) reality.
To test the latter, psychiatrists at Yale University decided to reproduce an experiment that was conducted in the 1890s on four groups of people - patients with psychosis (who did not hear voices), healthy people, patients with schizophrenia (hearing voices), and people who heard voices, not at the same time did not consider them to be something annoying.
Scientists have taught each of the study participants how to associate a chessboard with a sound of 1 kilohertz, which lasted only one second. Scientists changed the intensity of the sound, sometimes they turned it off altogether: in this case, the participants had to press a button at the moment when they heard the sound. In the course of the experiment, the scientists alternately decreased and increased the pressure on the participants in order to determine their degree of confidence. The researchers recorded brain activity at the time of decision making using MRI.
Psychiatrists suggested that people who usually hear voices will be more prone to auditory hallucinations, and their theory has found its confirmation: healthy people who, according to their testimonies, heard voices, as well as people with schizophrenia, heard a sound in its absence at about five times more often than other participants in the experiment. However, they were 28 percent more confident that they actually heard the sound.
Thanks to neuroimaging, it was found that these same participants in the experiment had abnormal brain activity in several areas of the brain that are responsible for tracking internal representations of reality. Moreover, the stronger the hallucinations were, the less activity was observed in the cerebellum. This part of the brain plays an important role in the coordination and planning of future movements; for this process, it is necessary to constantly update the perceptual image of the surrounding world.
The results of the study confirmed that a person's beliefs and ideas about the world around him can overcome the information that a person receives through the senses. By identifying the parts of the brain associated with hallucinations, the researchers note, therapies such as transcranial magnetic stimulation could be improved. In addition, according to scientists, it is more likely to apply the results of this kind of scientific research in the diagnosis of diseases: it may be easier for doctors to identify people with a predisposition to schizophrenia and to look for effective means for timely treatment.
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