Healthcare (Commonwealth Union) – Research carried out recently by psychologists at UNSW Sydney offers the most compelling evidence to date that auditory verbal hallucinations—commonly described as “hearing voices”—in schizophrenia may result from a disruption in the brain’s ability to recognize its own inner dialogue.
Appearing recently in Schizophrenia Bulletin, the study’s authors suggest that this discovery could mark an important step toward identifying biological markers that signal the presence of schizophrenia. This is particularly notable because, at present, there are no blood tests, brain scans, or other laboratory-based indicators that specifically identify the disorder.
Professor Thomas Whitford of the UNSW School of Psychology has long investigated how inner speech influences cognition in both healthy individuals and those with schizophrenia spectrum disorders.
He indicated that inner speech is essentially the voice inside your head that quietly narrates your thoughts—what you are doing, planning, or noticing and most individuals experience inner speech regularly, often without knowing it, though there are some who have no experience of it at all.
Professor Whitford further pointed out that their research demonstrates that when we speak – even if is within our heads – the section of the brain that processes sound from the external world ends up being less active.
He indicated that this is due to the fact that the brain forecasts the sound of our individual voice, however for individuals who hear voices, this forecast seems to go end up in errors, and the brain responds to the way it would react to the voice is coming from another person.
Professor Whitford indicated that this finding supports a long-standing hypothesis among mental health researchers: that auditory hallucinations in schizophrenia might arise when a person mistakenly perceives their own inner thoughts as voices coming from outside themselves.
He highlighted the fact that this concept has existed for half a century, but testing it has been extremely challenging because inner speech is naturally private.
“How do you measure it? One way is by using an EEG, which records the brain’s electrical activity. Even though we can’t hear inner speech, the brain still reacts to it – and in healthy people, using inner speech produces the same kind of reduction in brain activity as when they speak out loud.
“But in people who hear voices, that reduction of activity doesn’t happen. In fact, their brains react even more strongly to inner speech, as if it’s coming from someone else. That might help explain why the voices feel so real.”
The researchers placed people into three categories. The first consisted of 55 individuals with schizophrenia-spectrum conditions who had heard voices (auditory verbal hallucinations, or AVH) within the previous week. The second group contained 44 people with schizophrenia who either had never experienced AVH or had not had them recently. The third group served as a healthy control sample of 43 people with no history of schizophrenia.
All volunteers were hooked up to an EEG (electroencephalography) machine to record brain activity while they listened to sounds through headphones. At the moment they heard either “bah” or “bih” played, they were asked to internally generate one of those same syllables in their mind. Crucially, they had no advance knowledge of whether the sound delivered to their ears would align with the one they were mentally rehearsing.
Among the healthy controls, whenever the played sound matched the syllable they were silently “saying,” the EEG showed decreased activity in the auditory cortex — the brain region responsible for handling speech and sound. This reduction implies the brain had predicted the incoming sound and muted its response, similar to what happens during spoken speech.
In contrast, the pattern was flipped in participants who had recently experienced AVH. Rather than showing suppression of activity when the imagined syllable matched the sound heard, their auditory cortex response increased.
