Researchers have gained new insight into how and why some people become depressed, discovering that a particular brain network is much larger in people with the condition.
The surface of the brain is a communication junction box where different areas communicate with each other to carry out specific processes. But there is a finite amount of space that these networks can share.
Researchers now say that people with depression have a larger part of the brain involved in the network that controls attention to rewards and threats than people without depression.
“It takes up more space on the brain surface than we normally see in healthy controls,” said study co-author Dr. Charles Lynch of Weill Cornell Medicine in New York, adding that expansion meant that the size of other – often adjacent – brain networks was smaller.
To write in the journal NatureLynch and colleagues explain how they used precision functional mapping, a novel approach to brain imaging that involves analyzing a large number of functional MRI (fMRI) scans from each individual.
The team applied this method to 141 people with depression and 37 people without depression, allowing them to accurately measure the size of each participant’s brain networks. They then took the average size for each group.
They found that a part of the brain called the frontostriatal salience network was enlarged by an average of 73% in participants with depression, compared to healthy controls.
These findings were supported by an analysis of single brain scans previously collected from 932 healthy people and 299 with depression. The team said the size of this brain network in people with depression did not change with time, mood or transcranial magnetic stimulation treatment.
However, brain signals between different parts of the network became less synchronized when participants exhibited certain symptoms of depression. These changes were also associated with the severity of future symptoms.
The team added that an analysis of brain scans from 57 children who became depressed as adolescents showed that this brain network had been expanding for years before the first symptoms appeared. It was also expanded in adults with late-onset depression.
According to the researchers, this suggests that a more extensive brain network may be a risk factor for developing depression, rather than a consequence of the condition.
However, it is unclear to what extent this expanded network is the result of genetics or experience, and whether the link to depression arises from this expansion or from the fact that other brain networks become smaller as a result.
The team added that their findings could provide a way to investigate whether certain people are at increased risk of developing depression, and could also help in the development of personalized treatments.
But Prof Conor Liston, another author from Weill Cornell Medicine, said the results could benefit people with depression more broadly. “Having that information, that there is something identifiable in the brain that is associated with their depression and potentially poses a risk for their depression, is in itself quite reassuring for some people,” he said.
Dr Miriam Klein-Flügge of the University of Oxford, who was not involved in the research, said it was surprising that the study did not touch on the amygdala, a brain region that has been the focus of depression research for decades.
However, she said the new work was robust, important and exciting, and that it raised the question of whether it was possible to reverse an extensive frontostriatal salience network with early intervention.
According to Klein-Flügge, more research is needed to investigate whether the size of this network can actually be used to predict an individual’s risk of developing depression. He says it is unlikely that this is the only useful marker for predicting depression.
“But it is a useful step towards offering interventions to patients that can be delivered more quickly and that can be tailored to their individual needs,” she said.