Why do people with schizophrenia hear voices? A groundbreaking study suggests the brain misinterprets inner speech. Discover how EEG reveals this neural mix-up.
A recent study conducted by UNSW Sydney offers strong evidence that hearing voices may result from the brain misinterpreting its own internal thoughts as external sounds in people with schizophrenia. In simpler terms, thoughts that are usually silent inside the mind can be mistaken for actual sounds coming from outside.
This research could also help identify biological markers for schizophrenia, which currently lacks a unique blood test, brain scan, or laboratory-based indicator. It was published in the journal Schizophrenia Bulletin.
Inner Voice
Inner speech is the quiet voice that runs through your mind, narrating your thoughts, plans, or observations. For most people, the brain recognizes these thoughts as being self-generated. When we speak, even silently, the brain predicts the sound of our own voice and reduces activity in areas that process external sounds. However, in people who experience auditory hallucinations, this prediction system seems to fail, causing the brain to react as if the inner voice is coming from outside.
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Testing a Theory
The study supports a longstanding theory that hallucinated voices may be the result of a person's own thoughts being misidentified as external sounds. Until now, testing this idea has been challenging because inner speech is private. The researchers used EEG (electroencephalography) to measure brain activity and found that in healthy brains, there is a reduced response when the imagined sound matches the one played. In contrast, people who hear voices showed increased brain activity, as though the sound was coming from someone else.
To explore this further, participants were divided into three groups: those with schizophrenia who had recently experienced hallucinations, those with schizophrenia who had not, and healthy individuals. While wearing EEG caps, participants were asked to imagine simple sounds like “bah” or “bih” while listening to the same sounds through headphones.
Opposite Responses
In healthy participants, brain activity decreased when the imagined sound matched the one played. In contrast, participants who experienced hallucinations showed increased brain activity in the same situation, suggesting their brains treated the inner voice as if it were coming from outside. Those with schizophrenia who had not recently experienced hallucinations showed responses that were between the other two groups.
Future Impact
These findings offer the clearest evidence to date that auditory hallucinations may arise from the misinterpretation of inner speech. The researchers hope that measuring this specific brain response could help identify individuals at risk of psychosis earlier. Understanding these biological mechanisms is seen as a crucial step towards developing new and more effective treatments for schizophrenia.
