Selective Sound

Why do some people with schizophrenia hear voices?

- Hannah Seo

HEARING IMAGINARY VOICES is a common but mysterious feature of schizophrenia spectrum disorders. Up to 80 percent of people with these conditions experience auditory hallucinations, hearing speech or other sounds when there are none. Now research has gotten us closer to unraveling the brain mechanisms behind this phenomenon.

Experts have long thought auditory hallucinations arise from a person’s perception of their inner thoughts as real voices coming from the outside world. When people without schizophrenia speak or prepare to speak, the brain region that plans movements suppresses signals in the auditory cortex, the part of the brain that processes sound. This action helps people distinguish their own speech from external noise. Researchers theorized this mechanism could apply to healthy people’s inner speech as well—although that has been difficult to study and verify. Dysfunction in the activity between these brain regions might lead to hearing voices.

In a study published in Schizophrenia Bulletin, researchers demonstrated that inner speech indeed suppressed the brain’s auditory cortex in adults without schizophrenia. But in people with the condition who experienced auditory hallucinations, they found, inner speech boosted the auditory cortex’s response.