Hearing voices, or auditory hallucinations, is a common, distressing symptom of schizophrenia, a chronic brain disorder. New research published in NPJ Schizophrenia suggests these hallucinations are caused by an irregularity of the auditory system that develops during infancy.

“This is particularly exciting because it means that it might be possible to identify potentially vulnerable individuals, such as the offspring of schizophrenia patients, very early on,” Dr. Sophia Frangou, MD, PhD, a professor of psychiatry at the Icahn School of Medicine at Mount Sinai, in New York, said in a statement.

Schizophrenia, according to the American Psychiatric Association, is an incurable mental disorder with symptoms like “delusions, hallucinations, trouble with thinking and concentration, and lack of motivation.”

Auditory hallucinations affect more than 80% of schizophrenic patients and begin during adolescence. The voices that patients hear during these hallucinations sound very real to them and cause a severely negative impact on their quality of life — occasionally even pushing the patient towards self-harm, suicidal and violent actions. Researchers believe that beyond just identifying patients early, further research could shed more light upon methods like neuromodulation (altering nerve activity with stimuli like electricity and chemicals) to help patients experiencing these symptoms.

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The researchers used ultra-high-field imaging to compare the auditory cortex of people with schizophrenia and people without schizophrenia. Participants listened to tones ranging from very low to very high frequencies, and their brain activity was mapped by a powerful scanner. According to these brain activity maps, a healthy brain processed these sounds in a very organized manner — with each frequency activating a specific part of the auditory cortex. The map of these sounds in schizophrenic brains, however, appeared scrambled.

“Since auditory hallucinations feel like real voices, we wanted to test whether patients with such experiences have abnormalities in the auditory cortex, which is the part of the brain that processes real sounds from the external environment,” Dr. Fragnou said.

According to the researchers, these results meant that patients with schizophrenia who experienced auditory hallucinations could not properly process sound. This function, known as tonotopy, is established before an individual is born (in-utero) and during infancy.

“Because the tonotopic map is established when people are still infants and remains stable throughout life, our study findings suggest that the vulnerability to develop ‘voices’ is linked to a deviance in the organization of the auditory system that occurs during infancy and precedes speech development and the onset of psychotic symptoms by many years,” Dr. Fragnou said.