A new study suggests that a person’s vulnerability to hearing “voices” in schizophrenia may be established many years before symptoms begin, and possibly while still in the womb.
The findings are published in NPJ Schizophrenia, a Nature Partner Journal.
Hearing voices affects more than 80% of schizophrenia patients and is considered one of the most prevalent and distressing symptoms of schizophrenia. These auditory hallucinations, which usually begin in adolescence and young adulthood, sound very real to patients and can have a devastating impact on their quality of life, as the “voices” are typically distressing and distracting, sometimes compelling the person into suicidal or violent actions.
Uncovering the biological origins of auditory hallucinations is essential for reducing their contribution to the disease burden of schizophrenia.
To study the biological origins of hearing “voices” in patients with schizophrenia, a research team led by the Icahn School of Medicine at Mount Sinai used ultra-high field imaging to compare the auditory cortex of schizophrenia patients with healthy participants.
They found that schizophrenia patients who experienced auditory hallucinations had abnormal tonotopic organization of the auditory cortex. Tonotopy is the ordered representation of sound frequency in the auditory cortex, which is established in utero and infancy and which does not rely on higher-order cognitive operations.
The study findings suggest that the vulnerability to develop voices is probably established many years before symptoms begin.
“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,” said Sophia Frangou, M.D., Ph.D., Professor of Psychiatry at the Icahn School of Medicine at Mount Sinai. ”
Specifically, the researchers used an ultra-high field scanner with a powerful 7 Tesla magnet to produce high-resolution images of brain activity while participants listened passively to tones across a range of very low to very high frequencies.
In healthy brains, these sounds are processed in a very organized fashion; each frequency activates a specific part of the auditory cortex forming a tonotopic map.
The team obtained tonotopic maps from 16 patients with schizophrenia with a history of recurrent auditory hallucinations and 22 healthy participants. The team found that schizophrenia patients showed greater activation in response to most sound frequencies.
In addition, the mapping of most sound frequencies to parts of the auditory cortex appeared “scrambled” in patients with schizophrenia, suggesting that the normal processes for the organized representation of sound in the brain are disrupted in schizophrenia.
“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,” Frangou said.
“This is particularly exciting because it means that it might be possible to identify potential vulnerable individuals, such as the offspring of schizophrenia patients, very early on.”
According to the authors, in addition to helping doctors identify patients who are likely to experience hallucinations before the symptoms appear or become severe, the auditory cortex may be an area of consideration for novel treatment methods to help patients who already have symptoms.
Next, the team plans to repeat and expand the current observations in larger samples to determine their relevance to hallucinations across different diagnoses.