Acoustic hallucinations, imaginary voices that are perceived as real, originate from an alteration in brain connectivity between the areas of sensory and cognitive processing.
In a recent study, scientists at the University of Geneva have elucidated the cerebral origin of auditory hallucinations, a phenomenon that, in addition to appearing as a symptom in different mental pathologies, also frequently worries many people, who at some point in their lives think they hear voices or sounds without correlation in reality.
It is estimated that between 3% and 5% of the population of western industrialized countries have ever suffered episodes of acoustic hallucinations, well known to historical figures such as Socrates, Joan of Arc, or Carl Jung.
Swiss specialists have found an explanation, within the brain function, for a question that until now has been an unknown to science: auditory hallucinations would have their origin in an excessive increase in the connections established between the brain areas linked to the senses and those intended for linguistic processing.
This type of hallucination, in which voices or sounds suddenly appear without any kind of external stimuli, are in recurrent cases a symptom of schizophrenia, psychosis, and other neurological and psychiatric diseases. Until now the brain cause of these manifestations was unknown, which even some healthy people say they experience in isolation and occasionally.
Experts conducted a study using MRI images to collate reactions in about 100 healthy people and a similar number affected by so-called deletion syndrome, a disorder on chromosome 22 that increases markedly the risk of suffering sensory hallucinations and developing schizophrenia.
The team led by Stephan Eliez focused on checking if there were differences between both groups of people in the connections established between the thalamus and other areas of the brain. The thalamus plays a vital role in our sensory experiences since it is precisely the sector through which the information collected by the senses enters the brain.
Previous studies indicated that patients with schizophrenia had abnormal thalamic growth, but insufficient progress had been made in the thalamic nuclei and language-related brain sectors.
The finding of hyperconnectivity
The results of the comparisons yielded some strong data, such as that in people with deletion syndrome there was hyperconnectivity between the auditory cortex, the areas of the brain destined for language processing (mainly the Wernicke area), and some nuclei of the thalamus oriented to the transmission of auditory information.
The existence of these closer connections could then explain the appearance of recurrent auditory hallucinations in this type of pathology. Furthermore, scientists believe that by studying the relationship between the thalamus and the auditory cortex, it is possible to find new therapeutic strategies to improve the treatment of a large number of neuropsychiatric diseases.