Are Auditory Hallucinations Just Amplified Inner Voices?

The brain reacts to new sensory input with an evoked potential, seen the spike on the EEG above

Hallucinations may stem from our own inner voice

STUDY: Whitford TJ et al, Schizophrenia Bulletin 2025

STUDY TYPE: Case-control study (electrophysiological/EEG)

FUNDING: Public research councils in Australia, Hong Kong, and the US

Background

Researchers have long wondered if auditory hallucinations are caused by people with schizophrenia mistaking their own inner voice for external ones. Normally the brain quiets its response to self-generated speech, a pattern seen in EEG studies. This is the first study to use that technology in patients with active hallucinations.

The Study

• Participants silently produced a syllable (“baaa”) in their mind. EEG recorded brain activity in three situations: The inner voice on its own, the inner voice paired with the same sound (made externally by speakers), or the inner voice paired with a mismatched external sound.
• Three groups: 55 with schizophrenia-spectrum disorder and current hallucinations, 44 with the same diagnosis but no active hallucinations, and 43 healthy controls.

Results

To understand the results, you’ll need to know that the brain produces an evoked potential when it hears a novel sound (the up-down wave in the image below). The louder the sound, the larger the wave on EEG.

My first job in psychiatry was writing computer programs at NIMH to analyze these evoked potentials, circa 1993

When healthy controls made an internal sound that matched an external sound, their evoked potential was dampened. That’s the expected pattern. It is as if their brain is saying, “don’t pay attention to this, it’s just the voice in your head.”

Those with active hallucinations showed the opposite pattern. Their brain exaggerated its response when the inner voice was paired with the same external sound. In other words, they reacted to their inner voice as though it was part of the external sound, producing an exaggerated response just as they would if the volume was turned up on the speakers.

The more severe their clinical hallucinations, the more their brain amplified its response to the inner voice.

Patients without current hallucinations fell in between the two groups.

Limitations

Testing spanned two sites with different EEG systems. Sample size didn’t allow separating hallucination subtypes.

Practice Implications

1. There are probably multiple pathways to hallucinations. Earlier work showed that people with schizophrenia are unable to filter out irrelevant sounds. Without that filter, they may perceive patterns in outside noise, interpreting them as hallucinations.
2. This type of study may help some patients understand hallucinations as a signal-processing glitch, but that is difficult work.

—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report

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