In an article published in the journal Schizophrenia Bulletin, scientists linked these hallucinations to a malfunction in the brain mechanism that normally helps distinguish inner speech from external sounds.
Professor Thomas Whitford, who led the study, said that internal monologue is a "voice in our heads" that comments on our actions and thoughts. According to him, under normal circumstances, the brain identifies the source of the sound and reduces the response of the auditory cortex. But if this identification process malfunctions, a person may believe that their own thoughts in their head are intrusive voices coming from outside.
The study included 142 people divided into three groups: patients with schizophrenia and recent auditory hallucinations, patients with the same diagnosis but without hallucinations in recent days, and healthy volunteers. All participants were given specific tasks, during which their brain activity was recorded using electroencephalography (EEG). During the test, participants had to repeat the syllables "ba" or "b" to themselves while the same syllables were played through headphones. The matching between the internal and external audio was randomly selected.
In healthy participants, when internal and external sounds coincided, activity in the auditory cortex—where the brain recognizes its own voice—decreased. In people who had recently hallucinated, the opposite pattern was observed: Instead of being suppressed, the response was enhanced, as if the sound were coming from outside.
According to Professor Whitford, this indicates a breakdown in the brain's prediction function, causing internal speech to be mistakenly attributed to an external source.
The study's authors believe the results provide the most convincing confirmation of the hypothesis that "voices" in schizophrenia arise from distorted recognition of the patient's own speech.
This idea has been discussed for decades, but it has been difficult to test and verify because inner speech is a highly individualized process. Now, a direct physiological indicator has been provided. Researchers hope this technique will one day become a biomarker for early detection of psychosis and risk assessment.
