Hallucinations and delusions are common among schizophrenics, but now a new body of research reveals those who hear voices are susceptible because of a genetic malfunction. Researchers at St. Jude Children’s Hospital have discovered the reason behind hallucinating and hearing voices, a common symptom of schizophrenia patients. The study, which was published in the journal Science reveals, for the first time, how a specific circuit in the brain has been linked to hallucinations and delusions, which also explains why the drugs prescribed to treat schizophrenia work so well.
"We think that reducing the flow of information between these two brain structures that play a central role in processing auditory information, sets the stage for stress or other factors to come along and trigger the 'voices' that are the most common psychotic symptom of schizophrenia," said Dr. Stanislav Zakharenko, the study's co-author and associate member of the St. Jude Department of Developmental Neurobiology, in a press release.
Schizophrenia is considered a severe brain disorder that causes people to interpret reality through a defective filter. It often results in a combination of symptoms that include hallucinations, delusions, and a dysfunctional interpretation of thinking and behaviors of themselves and others, according to Mayo Clinic. It’s a serious, life-altering, chronic condition that requires lifelong treatment.
The defective neural circuits were observed in mouse models with genetic disorder 22q11 deletion syndrome, which occurs when part of chromosome 22 is missing. A healthy person usually has two chromosome 22 genes, but when one is missing there is a 30 percent chance that person will develop schizophrenia. This makes the missing chromosome the strongest risk factors for the disease.
Researchers looked at the auditory thalamus, which is what causes the hallucinatory voices. Antipsychotic drugs work well to bind with the D2 dopamine receptor (Drd2), which blocks the chemical messenger that causes the voices. However, it wasn’t clear until now exactly how or why the voices were triggered, they do know auditory messages travel through the brain using the primary auditory pathway, which links to the thalamus.
Mice with and without the missing chromosome 22 were observed. Researchers found stronger nerve impulses in the auditory thalamus of normal mice, compared to mice missing chromosome 22. Nerve impulses in the auditory thalamus were enhanced by antipsychotics for mice with a chromosome deletion. In a similar way, schizophrenic patients would have the "voices" calmed or muted inside their heads.
"These findings also integrate several competing models regarding changes in the brain that lead to this complex disorder," Zakharenko said.
Source: Chun S, Westmoreland JJ, Bayazitov IT, et al. Specific disruption of thalamic inputs to the auditory cortex in schizophrenia models. Science. 2014