Oct 04, 2024 12:30:00

The brain mechanism behind why schizophrenia patients hear 'auditory hallucinations' has been revealed

Schizophrenia, a mental illness that causes disorganized thinking and behavior, is characterized by a variety of symptoms, including hallucinations and delusions. Some

schizophrenic patients experience auditory hallucinations while others do not, and a Chinese research team has revealed the mechanism by which schizophrenic patients experience auditory hallucinations.

Impaired motor-to-sensory transformation mediates auditory hallucinations | PLOS Biology
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002836

What happens in the brain when a person with | EurekAlert!
https://www.eurekalert.org/news-releases/1059425

Scientists Identify Brain Signal Disruptions Behind Voices in Schizophrenia : ScienceAlert
https://www.sciencealert.com/scientists-identify-brain-signal-disruptions-behind-voices-in-schizophrenia

Fuyin Yang, a neuroscientist at Shanghai Jiao Tong University School of Medicine in China, and his colleagues conducted a study to investigate the mechanism by which schizophrenia patients hear auditory hallucinations. They examined the brains of 20 schizophrenia patients with auditory hallucinations and 20 schizophrenia patients without auditory hallucinations.

All subjects with schizophrenia were taking antipsychotic medication and were in a stable condition during the study. The researchers also used previously collected data from people without schizophrenia as a control group.

In the experiment, subjects were asked to listen to short syllables and then speak the same sounds. The brain activity data of the subjects during this process was analyzed to see what differences there were between subjects with auditory hallucinations and those without.

The analysis revealed clear differences between people without schizophrenia, schizophrenia patients without auditory hallucinations, and schizophrenia patients with auditory hallucinations.

After the subject's brain processes the sensory stimulus of 'hearing a sound,' it prepares to make the sound. In people without schizophrenia, the brain produces a signal called a '

corollary discharge ' that suppresses recognition of the sound they are about to make, and an ' efference copy ' that instructs the body to make the sound.

However, in all schizophrenia patients, the 'concomitant discharge' that suppresses the recognition of the sounds they make was lost. This makes it easier for schizophrenia patients to recognize the sounds they make as 'sounds heard from outside.' This phenomenon has also been confirmed in

schizophrenic mice . However, in schizophrenia patients without auditory hallucinations, the efference copy functioned normally.

On the other hand, in schizophrenia patients with auditory hallucinations, the efference copy was stronger than normal, even for 'internal speech' that was not intended to be produced by the patient's own mouth. The combination of this reduced contingent discharge and the strengthening of the efference copy may make it easier for schizophrenia patients to mistake their 'internal speech' for sounds heard from outside, which may be the cause of the 'auditory hallucinations,' the research team concluded.

'People suffering from auditory hallucinations are able to 'hear' sounds without any external stimuli. Disruption of the functional connections between the motor and auditory systems in the brain leads to a loss of the ability to distinguish fantasy from reality,' the researchers said.