Here is why some schizophrenics hear voices

Hearing voices often seems strange. What is actually happening in the brain of people with schizophrenia when they perceive these sounds? Researchers may have finally found an explanation.

A new study reveals that the voices heard by schizophrenic patients may be caused by very specific brain dysfunctions. These anomalies seem to play a key role in the confusion between internal and external sounds.


Two brain processes are implicated: corollary discharge and efference copy. The main function of the former is to attenuate the perception of self-generated sounds, such as an individual's own voice. Normally, it prevents a person from hearing their own voice intrusively. However, in patients with schizophrenia, this mechanism does not work properly. Instead of reducing the impact of these internal sounds, it amplifies them, making their own voice much louder and more present.

The efference copy, on the other hand, is an internal signal the brain uses to anticipate the sounds it is about to produce, especially during speech. It plays a crucial role in preparing the auditory system to receive these anticipated sounds, thus allowing a distinction between internal and external sounds.

However, in schizophrenic patients, this mechanism is profoundly altered. This signal is not only amplified but also distorted, making the anticipated internal sounds far louder and more "real" than they should be. This exaggeration of brain-generated sounds causes confusion between internal thoughts and voices perceived as coming from the outside, leading to the auditory hallucinations characteristic of schizophrenia.

Researchers at New York University in Shanghai conducted a study to observe brain dysfunctions in schizophrenic patients, whether or not they experienced auditory hallucinations. The sample included 40 participants, divided into two groups: 20 patients with hallucinations and 20 others without symptoms. Brain activity was measured by electroencephalogram (EEG).

The results showed significant anomalies in corollary discharge and efference copy in patients with hallucinations, while these dysfunctions were less pronounced in those without hallucinations. These results confirm the direct role of these mechanisms in the perception of voices.

These findings open the door to potential new treatments. By targeting these failing mechanisms, it might be possible to reduce the intensity or frequency of auditory hallucinations in people with schizophrenia. It also appears that dysfunctions in the connections between the brain's motor and auditory systems play a key role.

This suggests new therapeutic approaches, focusing on these neural links rather than solely on the auditory system.