Summary: People with schizophrenia who experience auditory hallucinations show increased activation in parts of the auditory cortex and a disrupted, or “scrambled,” mapping of sound frequency. Because the tonotopic map of the auditory cortex is formed in infancy and remains largely stable across life, these findings suggest that the vulnerability to develop auditory hallucinations may originate from atypical auditory system organization established during early development—well before speech emerges and long before psychiatric symptoms appear.
Source: Mount Sinai Hospital
Overview: Auditory hallucinations—commonly described as “hearing voices”—affect a large majority of people with schizophrenia and are among the most distressing and disruptive symptoms of the illness. These experiences typically begin in adolescence or young adulthood, and the voices can feel indistinguishable from real external sounds. They often interfere with daily life and can contribute to serious outcomes, including risk of self-harm or aggression. Identifying the biological origins of these hallucinations is essential to improve diagnosis, prevention, and treatment.
To explore whether abnormalities in the brain’s early auditory processing contribute to the perception of voices, researchers at the Icahn School of Medicine at Mount Sinai used ultra-high field magnetic resonance imaging to examine the auditory cortex of people with schizophrenia compared with healthy controls. The study focused on tonotopy—the organized mapping of sound frequency across the auditory cortex. Tonotopic organization develops very early, beginning prenatally and during infancy, and reflects basic sensory representation rather than higher-order cognitive activity.
The research team used a 7 Tesla MRI scanner to achieve high-resolution functional images while participants passively listened to a series of tones spanning very low to very high frequencies. In typical brains, different sound frequencies consistently activate specific regions of the auditory cortex, producing a clear tonotopic map. The study collected tonotopic maps from 16 people with schizophrenia who had a history of recurrent auditory hallucinations and 22 healthy participants.
Compared with controls, participants with schizophrenia showed greater overall activation in response to most frequencies. More notably, the normal orderly mapping of frequencies across the auditory cortex appeared disrupted in many patients—frequencies that should activate particular cortical locations were instead mapped irregularly. In other words, the tonotopic map appeared “scrambled,” indicating a breakdown in the auditory cortex’s usual organized representation of sound.
Because tonotopy is established in infancy and remains stable through life, these results point to a model where the risk for auditory hallucinations may be rooted in atypical auditory cortex organization early in development. This deviance would precede both the development of speech and the emergence of psychotic symptoms by many years. Identifying such early markers could make it possible to detect individuals at elevated risk—such as children of people with schizophrenia—long before hallucinations begin.
The investigators note two important implications. First, tonotopic disruption in the auditory cortex could serve as an early biomarker to identify individuals more likely to develop auditory hallucinations. Second, the auditory cortex itself might be a target for future therapeutic approaches, including neuromodulation techniques aimed at restoring more typical auditory processing for people who already experience hallucinations.
Future work from Dr. Sophia Frangou’s team will seek to replicate and extend these observations in larger, more diverse samples. Planned studies aim to determine whether similar tonotopic abnormalities are present across diagnostic categories that include auditory hallucinations and to relate the degree of tonotopic disruption to auditory cortical activation and connectivity during actual hallucinatory episodes.
Study details: The study used passive listening to tones across the range 88–8000 Hz and took advantage of the high spatial resolution provided by 7 Tesla functional imaging to reveal both increased activation and altered tonotopic organization in the auditory cortex of schizophrenia patients with recurrent hallucinations.
Funding: This research was supported by the National Institutes of Mental Health, the National Cancer Institute, The Netherlands Organisation for Health Research and Development, the Stanley Foundation, and the Brain and Behavior Research Foundation.
Source:
Mount Sinai Hospital
Media Contacts:
Elizabeth Dowling – Mount Sinai Hospital
Image source:
The image is in the public domain.
Original Research: Open access — “Abnormal auditory tonotopy in patients with schizophrenia”. Authors: Gaelle E. Doucet, Maxwell J. Luber, Priti Balchandani, Iris E. Sommer & Sophia Frangou. NPJ Schizophrenia. DOI: 10.1038/s41537-019-0084-x.
Abstract (concise): Auditory hallucinations are common and distressing in schizophrenia. Using ultra-high field 7 Tesla imaging, the study found that patients with recurrent hallucinations show abnormally increased auditory cortical activation and altered tonotopic maps during passive listening to tones (88–8000 Hz). These findings suggest that predisposition to hearing voices may reflect early-development alterations in auditory cortex organization and point to potential biomarkers for early identification of vulnerable individuals.