Some people with severe mental illness, especially schizophrenia, hear “voices,” also known as auditory hallucinations.
This symptom, which is present in more than 80% of schizophrenics, is one of the most threatening. Hallucinations sound very realistic, usually upsetting and distracting the patient, and sometimes forcing him to commit suicidal or violent acts.
Disclosing the biological origin of auditory hallucinations is vital to reducing the risk of irreversible effects of the disease.
The team headed by researchers from the Ikana School of Medicine of Mount Sinai Center took on the task. Scientists have found that patients with schizophrenia experiencing auditory hallucinations have an abnormal tonotopic organization of the auditory cortex.
Tonotopy is an ordered representation of the frequencies of sound in the auditory cortex, which is laid in the womb and further in infancy, and does not depend on cognitive operations of a higher order.
“Since auditory hallucinations feel like real voices, we wanted to check if patients with such experiences have abnormalities in the auditory cortex – the area of the brain that processes real sounds from the external environment,” says Sofia Frangu, MD and professor of psychiatry at the School of Medicine Icana Mount Sinai.
The researchers gathered a small group of patients with schizophrenia and healthy people and used the 7-Tesla heavy-duty MRI scanner to obtain images of their brain activity with a high degree of resolution.
During the scan, study participants passively listened to tones ranging from very low to very high frequencies.
Sounds are processed in a very organized manner in a healthy brain: each frequency activates a certain part of the auditory cortex, forming a tonotopic map.
At the end of the session, the team of scientists received tonotopic maps of 16 patients with schizophrenia and a history of recurrent auditory hallucinations, as well as 22 healthy participants.
Schizophrenics have been found to show inadequately wide activation in response to most sound frequencies.
In addition, the mapping of most sound frequencies in the auditory cortex of patients with schizophrenia was completely chaotic. This suggests that the disease disrupts the normal processes of organized presentation of sound in the brain.
“Since the tonotopic map is installed in infancy and remains stable throughout life, our results mean only one thing – vulnerability to the development of“ voices ”is associated with an early deviation in the organization of the auditory system that occurs immediately after birth or even before birth. This is very interesting, because in this way it will be possible to identify potentially vulnerable people, for example, among children of patients with schizophrenia, ”says Dr. Frangu.
However, not only diagnosis, but also treatment is potentially possible. For example, some methods of neuromodulation of the auditory cortex could help people with pre-existing symptoms.
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