Hallucinations arise due to an increase in the normal functioning of the brain - when assessing what is happening, rely on already available information and predictions. British scientists, authors of an article in the journal Proceedings of National Academy of Sciences (PNAS), came to this conclusion during the experiments.
The human brain has a powerful ability to "complete" the picture of what is happening, relying on incomplete and ambiguous information. For example, when entering a dark room, a person can easily guess that the dark spot that quickly flew behind a distant sofa is his cat. In the process of such recognition, new visual data play a minimal role (as opposed to background knowledge). However, a side effect of the “predictive brain” is the tendency to see things that don't really exist in reality, that is, hallucinations. Moreover, this kind of distorted perception is inherent not only to mentally ill people - almost everyone has heard or seen something illusory, scientists say.
To learn about the relationship of such mispredictions to mental illness, the researchers worked with 18 psychiatric patients who were diagnosed with early signs of psychosis. Psychosis is a pronounced disorder of mental activity, in which mental reactions grossly contradict the real situation, which is reflected in the disorder of perception of the real world and disorganized behavior. Patients, as well as 16 healthy volunteers, were shown several black and white pictures depicting incomprehensible objects. Participants in the experiment were asked in which pictures you can see the silhouette of a person.
Then the volunteers were shown color images, on the basis of which black and white pictures were built. People who are prone to psychosis and hallucinations should make better use of this information - for the reason that hallucinations stem from a hypertrophied tendency to extend previously existing ideas to reality, scientists decided.
This hypothesis was fully confirmed: patients with a tendency to psychosis were better at using additional information (color images) and more quickly at identifying human silhouettes in black and white images. An additional experiment involving 40 healthy people, with varying degrees of psychosis, confirmed the original findings. Moreover, a potentially dangerous shift in the mechanism of information processing (when the original data for the brain becomes more important than the new ones received by the senses) can be determined even before the onset of psychosis - which makes it easier to prevent this disorder.
“The emergence of key symptoms of mental illness can be understood as a shift in the balance of normal brain function. More importantly, such symptoms and sensations do not indicate a “broken” brain, but a brain that is trying - in the most natural way - to make sense of ambiguous data,”said co-author Naresh Subramaniam.