How Do Brains Create Auditory Hallucinations? Novel Robotic Procedure Can Induce Hearing Voices That Are Not Real

Researchers at école Polytechnique Fédérale de Lausanne and the University Savoie Mont Blanc have discovered that it's possible to induce auditory hallucinations in mentally healthy individuals under specific conditions. Their experiments used robotic assistance to induce auditory-verbal hallucinations in volunteers, shedding light on how the brain can create such experiences.

Their findings provide fascinating insights into the human brain's capacity to generate hallucinations in healthy individuals. The study, published in Psychological Medicine, reveals the potential for a robotic procedure to induce auditory-verbal hallucinations (AVH) in a controlled experiment.

Inducing Auditory-Verbal Hallucinations

The study explored the triggers of AVH, the perception of voices or sounds without an external source, which are associated with various psychiatric disorders. Previous research linked these hallucinations to disruptions in self-monitoring processes in the brain, where internal actions or thoughts are misattributed as externally generated, resulting in perceived voices.

Overcoming methodological challenges in studying hallucinations, the research aimed to induce them in a controlled laboratory environment in real-time, repeatedly, and within a short duration.

This focused investigation specifically on "hearing voices," a common and distressing psychotic symptom, addressing the limitations of prior studies conducted primarily on patients and differentiating hallucination effects from those of other clinical conditions.

To explore the induction of AVH in a controlled laboratory environment, the team developed a new method integrating voice perception and sensorimotor stimulation.

Building on a prior technique where participants pressed a button, and a robotic arm poked them in the back, this experiment involved 48 participants experiencing variable poke delays while wearing headphones playing a combination of "pink noise" akin to waterfall sounds and occasional voice snippets, including their own and others'.

During the experiments, some participants not only reported a sense of presence due to the poking but also claimed to hear voices through the headphones, despite the absence of actual voices. The phenomenon of hearing voices was more common when participants heard another person's voice before their own and when there was a delay between button pressing and arm poking.

These findings lend support to both hypotheses about the triggers of hallucinations, indicating that participants had difficulty accurately monitoring their surroundings and were influenced by their strong beliefs about ongoing events.

Additionally, the frequency of hearing hallucinated voices increased as the experiments continued, making participants more likely to experience phantom sounds as the session progressed.

More About Auditory Hallucinations

Auditory hallucinations, the perception of sounds or voices without an external source, can vary in frequency and character, occurring both in individuals with mental health conditions and those without. Approximately 5% to 28% of people in the United States experience auditory hallucinations, making them the most common type of hallucination.

There are two primary forms: verbal (hearing voices) and hearing sounds or noises. Auditory verbal hallucinations can manifest differently from person to person and may come from various sources, including external sounds or internal mental events. They are most commonly associated with schizophrenia but can occur in individuals without mental health conditions.

Hearing sounds or noises represents another category of auditory hallucinations, encompassing diverse auditory experiences such as music, animal calls, or background noises. The volume of the perceived sounds can range from quiet to loud. The treatment for auditory hallucinations depends on their underlying cause.

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