New study confirms 50-year-old theory. The brain of those suffering from schizophrenia confuses inner and outer voices.
An old theory that seeks to explain why people with schizophrenia hear voices has finally been confirmed.
Researchers at the University of New South Wales have demonstrated that auditory hallucinations occur when the brain misinterprets inner speech as if it came from an external source.
The idea, proposed five decades ago, was difficult to prove because inner speech is an obviously private process, impossible to analyze directly. But under the leadership of psychologist Thomas Whitford, the team used electroencephalography (EEG) to monitor brain activity and examine how people with schizophrenia process internal and external sounds.
Normally, when a person speaks out loud or just mentally, the brain reduces activity in the areas responsible for processing external sounds, anticipating the sound of one’s own voice. But Whitford’s study revealed that in individuals who suffer from auditory hallucinations, this prediction mechanism fails. Instead, the brain reacts to inner speech as if it were produced by someone else.
The study involved 142 participants divided into three groups: people with schizophrenia who have had recent hallucinations, people with schizophrenia without recent hallucinations and a control group with no history of the illness. Participants listened to recorded syllables (“bah” or “bih”) while mentally repeating one of those same syllables. EEG measurements showed that those with recent hallucinations had significantly stronger brain reactions when their inner speech matched the sound they heard.
According to Whitford, this anomalous brain response may explain why hallucinated voices seem so real.
The conclusions of the investigation this Tuesday in Schizophrenia Bulletin not only validate a long-standing hypothesis, but also pave the way for new, innovative clinical benefits: identifying early neurological markers of psychosis could make it possible to detect and treat schizophrenia before severe symptoms emerge.
