A new study finds a connection between damage to networks at the back of the brain and common mental illnesses
"We found that lesions to those regions [anterior cingulate and insula] were correlated with less psychiatric illness, not more, so atrophy in that cingulate and insula may be a consequence or a compensation for psychiatric illness rather than a cause of it,” he said. Dr Joseph Taylor, associate psychiatrist, Brigham’s Department of Psychiatry
Disturbances to one network of brain regions may be involved in the onset of six mental health conditions, according to an analysis of existing collections of medical data.
In the past, studies that involved scanning the brain have suggested links between several different areas of the brain and certain mental health conditions, but the results were inconsistent. Dr Joseph Taylor, an associate psychiatrist, and his colleagues at Brigham and Women’s Hospital in Boston wondered if that was because different regions in a single network could all play a role.
The research, published in Nature Human Behaviour, involved carrying out a meta-analysis of 193 brain-scanning studies involving nearly 16,000 people. This showed that individuals with any one of six mental health conditions (depression, anxiety, schizophrenia, bipolar disorder, addiction or obsessive-compulsive disorder) tended to have shrunken tissue in the regions at the front.
The team compared its findings with an existing map of brain connections, known as a connectome, to test whether grey matter changes in psychiatric illness more effectively mapped to a common brain network than to common brain regions. (Whereas a brain region is a self-contained area, a brain network involves several regions working together.) This showed that when the identified regions at the back of the brain have low activity, the ones at the front tend to have high activity, and vice versa.
They then looked at the health records and brain scans of 194 Vietnam war veterans, some of whom had a penetrating head trauma. They found that the veterans were more likely to be diagnosed with one of the six mental illnesses if the injury had occurred in regions towards the back of the brain, in particular in the posterior parietal cortex, which is linked with spatial perception.
They were less likely to have such a diagnosis if they had been injured near the front of the brain, including in the anterior cingulate, a region associated with emotions, and the insula, which is linked with self-awareness.
The two sets of findings – from the meta-analysis and the analysis of the veterans’ brain scans – suggest that in people without any mental health condition, the back regions of the brain inhibit the front regions, while in people with damage to the back regions, the front regions become too active, which may lead to mental illness and tissue shrinkage.
Taylor said that the team’s findings challenged the idea that grey matter decreases in anterior cingulate and insula are causally related to psychiatric illness. “We found that lesions to those regions were correlated with less psychiatric illness, not more, so atrophy in that cingulate and insula may be a consequence or a compensation for psychiatric illness rather than a cause of it,” he said.
He and his colleagues refer to the circuit as the “transdiagnostic network” because it seems to be involved in so many different psychiatric diagnoses. He is planning to boost brain activity in the posterior regions by using a technique called transcranial magnetic stimulation as a potential treatment for mental illnesses.
This is an interesting piece of research that shows the value of analysing medical scans in tandem with patient records. The finding that damage to the back of the brain is more likely to be correlated with particular mental illnesses is potentially groundbreaking and may lead to better treatment in future. We do need to be cautious about jumping to conclusions, however – the relationship between damage to the brain and mental illness is complex, and more research is needed.