Hearing Voices and the Inner Monologue Can Get Mixed Up for Those with Schizophrenia

If you hear a voice when no one is speaking, then you may be experiencing an auditory verbal hallucination (AVH). These hallucinations are common in patients with schizophrenia, although the explanation of why and how these hallucinations occur has long perplexed scientists.

This week, an article published in the Schizophrenia Bulletin suggested that scientists have finally found an answer, having gathered clear evidence that AVH could arise from the mind’s misinterpretation of one’s own monologue or inner voice – the silent stream of internal thoughts involved in one’s ability to solve problems, make plans, reflect and self-regulate.

“Our research shows that when we speak – even just in our head – the part of the brain that processes sounds from the outside world becomes less active. This is because the brain predicts the sound of our own voice,” Thomas Whitford, study author and professor at the school of psychology at the University of New South Wales in Sydney, Australia, said in a statement released with the research. “But in people who hear voices, this prediction seems to be wrong and the brain reacts as if the voice was coming from someone else.”

Learn more: You might be hallucinating right now

React to internal voices

Historically, it has been theorized that schizophrenia patients with AVH have these hallucinations because their brain has difficulty identifying their internal voice, confusing it with the sound of an external speaker.

“This idea has been around for 50 years,” Whitford said in the release, “but it has been very difficult to test because inner speech is inherently private.”

To solve this problem, Whitford and his team turned to electroencephalography (EEG) as a method to measure people’s responses to their own internal monologues.

“Even though we can’t hear inner speech, the brain responds to it,” he added in the statement, suggesting the technology could clarify whether people with AVH regularly respond to their internal voices.

Measure the monologue

Bringing together a total of 142 participants, including participants without schizophrenia and AVH and with schizophrenia and AVH, among others, Whitford and his team set out to measure their inner vocal responses. By connecting each person to an EEG device, the scientists prompted the participants to imagine making a single-syllable sound, “bah” or “bih,” in their minds. Each time participants imagined making one of two sounds, they heard one through a pair of headphones, although it wasn’t always the same sound they imagined.

It is important to note that when imagined and heard sounds matched, participants without schizophrenia and AVH demonstrated decreased activity in their auditory cortex, suggesting that they were anticipating the sound (much like what would happen if they said something out loud), while participants with schizophrenia and AVH showed increased activity in this same area, suggesting that the sound startled them.

“Their brains responded more strongly to inner speech that matched the external sound,” Whitford said of the participants experiencing hallucinations in the release. “This reversal of the normal suppression effect suggests that the brain’s prediction mechanism may be disrupted in people currently experiencing auditory hallucinations, which could cause their own inner voice to be misinterpreted as external speech.”

Learn more: Scientists don’t know exactly how the inner voice works

A clear and conclusive test?

Taken together, the results seem to suggest that people with AVH perceive their internal voice as an external voice. “This has always been a plausible theory – that people were hearing their own thoughts spoken out loud,” Whitford said in the release. “But this new approach has provided the strongest and most direct test of this theory yet.”

In the future, Whitford and his team hope to discover whether this reversed response to self-talk could be a clear biomarker for schizophrenia, a disease for which currently lacks a conclusive biological indicator that could be measured with a simple brain or blood test.

“This type of measurement has great potential to become a biomarker,” Whitford added in the release. “Ultimately, I think understanding the biological causes of schizophrenia symptoms is a necessary first step if we hope to develop effective new treatments.”

Learn more: Do you have an inner voice? Science can’t agree if everyone agrees

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