Scientists have uncovered differences in the brains of people with schizophrenia who do and do not have hallucinations.
Dr. Jon Simons and colleagues at Cambridge University, UK, looked at structural MRI (magnetic resonance imaging) scans of 153 individual brains: 113 scans were from people with schizophrenia and 40 from similar participants without schizophrenia. Among the schizophrenia patients, 78 had a history of hallucinations and 34 did not.
The team measured the length of the paracingulate sulcus (PCS), a fold toward the front of the brain, in each scan. This indicated a link between length of the PCS and the tendency to hallucinate.
On average, the patients suffering hallucinations had a PCS that was about two centimeters shorter than those without hallucinations, and three centimeters shorter than the non-schizophrenic group.
This suggests that a one centimeter reduction in the fold’s length is linked to a 20 percent rise in the chance of hallucinations. The association applied to both auditory and visual hallucinations.
Dr. Simons explained that the team selected patients to put into each group such that those two groups were as directly comparable as possible. Factors such as age, sex, medication, and even whether participants were left- or right-handed were all taken into account.
“So as close as we can get it,” Dr. Simons said, “the only difference between those two groups is that one group experiences hallucinations and the other one doesn’t.”
The team says this is consistent with an explanation based on “reality monitoring.” The PCS is thought to play a role in distinguishing self-generated information from that perceived in the outside world.
Details are published in the journal Nature Communications.
In scans of healthy people, Dr. Simons has previously found that variation in the length of the PCS was linked to reality monitoring.
He says, “Schizophrenia is a complex spectrum of conditions that is associated with many differences throughout the brain, so it can be difficult to make specific links between brain areas and the symptoms that are often observed.
“By comparing brain structure in a large number of people diagnosed with schizophrenia with and without the experience of hallucinations, we have been able to identify a particular brain region that seems to be associated with a key symptom of the disorder.”
Changes in other areas of the brain are likely also important in generating the complex phenomena of hallucinations, he adds.
If further work shows that the difference can be detected before the onset of symptoms, it might be possible to offer extra support to people who face that elevated risk.
But hallucinations are just one of the main symptoms of schizophrenia, and patients are diagnosed on the basis of other irregular thought processes.
Researcher Dr. Jane Garrison says the PCS is one of the last structural folds to develop in the brain before birth, and varies in size between individuals.
She adds, “We think that the PCS is involved in brain networks that help us recognize information that has been generated ourselves. People with a shorter PCS seem less able to distinguish the origin of such information, and appear more likely to experience it as having been generated externally.
“Hallucinations are very complex phenomena that are a hallmark of mental illness and, in different forms, are also quite common across the general population. There is likely to be more than one explanation for why they arise, but this finding seems to help explain why some people experience things that are not actually real.”
The team concludes that, “To be able to pin such a key symptom to a relatively specific part of the brain is quite unusual.”
Commenting on the work, Professor Stephen Lawrie of the University of Edinburgh, UK, states, “There’s quite a strong literature showing that auditory hallucinations are related to dysfunction or structural disruption in language areas of the brain.
“I think the value of this is that it probably helps us think slightly more broadly about hallucinations in schizophrenia, in terms of it not just being about language areas of the brain, but involving a more distributed network of regions, and implicating, in particular, cognitive control or higher-order cognitive functioning.”
Professor Lawrie has also studied brain structure in relation to schizophrenia and hallucinations.
He says the form and content of hallucinations can vary considerably between patients and believes that different brain changes may reflect these different processes. His work has found indications for a role for the lateral temporal cortex in hallucinations.
This type of investigation “may have relevance for the understanding of the biological basis of the disorder,” he concludes.
Garrison, J. R. et al. Paracingulate sulcus morphology is associated with hallucinations in the human brain. Nature Communications, 17 November 2015 doi: 10.1038/NCOMMS9956
Whalley, H. C. et al. Correlations between fMRI activation and individual psychotic symptoms in un-medicated subjects at high genetic risk of schizophrenia. BMC Psychiatry. 29 October 2007 doi: 10.1186/1471-244X-7-61
MRI of the brain photo by shutterstock.