One of the symptoms of schizophrenia is auditory hallucinations – patients report hearing voices of “invisible” people in their heads. Some people with schizophrenia also have trouble distinguishing the “voices” in their heads from their own thoughts, causing them to think that their thoughts are being voiced by an invisible person. Until recently, scientists did not know the nature of these hallucinations, which made them difficult to treat. Now, it seems, a group of Chinese researchers has found the answer to this question. This discovery could be a turning point for scientists working on treating auditory hallucinations.
Scientists have found out why auditory hallucinations occur in schizophrenia. Photo source: chastnaya-psihiatricheskaya-klinika-stacionar.ru
How people distinguish their own voice from someone else's
According to previous studies, the problem of auditory hallucinations may be related to a specific brain signal called the corollary discharge (CD). In healthy people, this signal allows them to distinguish sounds made by their own voice from the voices of other people. Perhaps for this reason, when you hear your voice on a recording, it seems very distorted to you, and not at all the same as you hear it in real life. That is, the brain somewhat distorts the perception of its own voice.
However, in most people with schizophrenia, this signal usually does not work. But the authors of the new study do not agree with such conclusions. The fact is that the lack of inhibition in itself cannot cause hallucinatory symptoms.
People with schizophrenia may have difficulty distinguishing their own thoughts from voices. Photo source: fishki.net
To find out what actually causes hallucinations, researchers at Shanghai Jiaotong University examined the brains of 20 schizophrenia patients who complained of auditory hallucinations, as well as the brains of another 20 schizophrenia patients who did not have auditory hallucinations. The authors also recruited people who did not have schizophrenia as a control group.
Why Auditory Hallucinations Occur
The researchers first compared the brain activity of all the people, based on data obtained using an electroencephalogram. Then volunteers from all three groups were given a pre-recorded syllable to listen to. This allowed the team to find differences in brain function that could be responsible for auditory hallucinations.
As the authors of the study, published in the journal PLOS Biology, report, in both groups of people with schizophrenia, the scientists found comparatively low activity of the CD signal, which was mentioned above. This indeed disproved the version that it is this signal that causes auditory hallucinations. But why do they occur then?
Excessive activity of some neurons turns a person's thoughts into auditory hallucinations. Source: psyfactor.org
During the study, the scientists found that only the patients who heard voices had an overactive efference copy, or so-called motor signal (EC). As the researchers explain, when a person wants to speak, the motor system generates a precise signal and sends it to the auditory system. Thanks to this, a person can accurately predict a sound before saying it.
Because of the overactivity of this signal, some people with schizophrenia “play” not the sound they are going to say, but any random internal “brain chatter.” This happens because the uncontrolled accompanying signal misinterprets neural activity.
Simply put, the EC signal, acting on the auditory system, “voices” the person’s own thoughts, resulting in a hallucination. At the same time, due to the suppressed DC signal, the person does not distinguish his own voice from someone else’s. That is, the combination of two factors causes realistic hallucinations.
New discovery may help treat auditory hallucinations. Photo source: oknakg.ru
Auditory hallucinations may be treatable
Although hallucinations are called “auditory,” they are not actually caused by the auditory system. From all of the above, it follows that the changes that scientists have discovered in the brains of people with schizophrenia and auditory hallucinations blur the line between internal and external reality. People with this disease simply do not distinguish external voices from their own thoughts.
The problem occurs in the network connections from motor to auditory. Therefore, treatment aimed at the auditory system may be ineffective. If scientists are right in these conclusions, auditory hallucinations can be eliminated by suppressing the EC signal, for example, with drugs. Therefore, researchers hope that a new understanding of the mechanisms underlying auditory hallucinations will allow the development of new, more effective treatments.
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Finally, we note that scientists to this day do not even fully know the causes of schizophrenia itself. For example, a number of studies indicate that the risk of developing this disease is increased in people who were bitten by a cat as children. But the opinion that a lack of vitamins causes schizophrenia turned out to be erroneous. In fact, a lack of vitamins causes another disease with similar symptoms.