THE ESSENTIAL
- In people with schizophrenia, auditory hallucinations are thought to be due to two brain abnormalities: a faulty corollary discharge, which normally suppresses the perception of their own voice, and an amplified efferent copy, making internal sounds more intense than they are.
- This inability to clearly distinguish internal and external sounds causes, in people with schizophrenia, confusion between their own thoughts and voices perceived as coming from outside, their phantom voices.
- The study suggests that targeting these mechanisms could lead to new treatments to reduce auditory hallucinations in schizophrenia patients.
People with schizophrenia often hear voices in the absence of any external sound source. A new study, published in the journal PLOS Biologysheds a little more light on the mechanisms of the brain – and its faulty processes – which are hidden behind these auditory hallucinations.
Two brain processes disrupted in schizophrenics
In a healthy person, when one prepares to speak, the brain sends a signal called “corollary discharge”, which suppresses the perception of one’s own voice. This mechanism makes it possible to distinguish sounds produced by oneself from sounds coming from outside. But this new research, led by scientists at New York University Shanghai (China), shows that in schizophrenia patients who hear voices, this corollary discharge does not work properly: instead of suppressing these internal sounds, the brain of patients amplifies their perception, according to a press release.
At the same time, researchers have highlighted another anomaly: the “efferent copy”. This signal is a kind of internal draft of the sounds that a person plans to produce. But in patients suffering from auditory hallucinations, this efferent copy is amplified, noisier. In other words, the brain hears these internal sounds as if they are louder – or more “real” – than they actually are.
Better treat patients’ auditory hallucinations
The inability to clearly distinguish internal and external sounds causes, in people with schizophrenia, confusion between their own thoughts and voices perceived as coming from outside, their phantom voices. The scientists observed this difference by comparing, using an electroencephalogram, the brain waves of 20 schizophrenia patients with auditory hallucinations and 20 other schizophrenia patients who had never had such symptoms.
It appears that the dysfunction of the functional connections between the motor (responsible for speech) and auditory (responsible for listening) systems seems to play a central role in this inability to distinguish reality and imagination.
Understanding these mechanisms could, according to the research team, open the way to new therapeutic approaches for schizophrenia patients suffering from auditory hallucinations. By targeting the defective processes of corollary discharge and efferent copying, it would be possible to reduce the frequency or intensity of the voices heard by these patients.
