Researchers have gained new insight into how and why some people experience depression after finding a particular brain network is much larger in people living with the condition.
The surface of the brain is a communication junction box where different areas talk to each other to carry out specific processes. But there is a limited amount of space for these networks to share.
Now researchers say that in people with depression, a larger part of the brain is involved in the network that controls attention to rewards and threats than in those without depression.
“It takes up more real estate on the brain surface than what we see is typical in healthy controls,” said Dr. Charles Lynch, a co-author of the research, from Weill Cornell Medicine in New York. He added that expansion means that the size of other – often neighboring – brain networks is smaller.
Write in the journal NatureLynch and colleagues report how they used precision functional mapping, a new approach to brain imaging that analyzes an army of fMRI (functional MRI) scans of each individual.
The team applied this method to 141 people with depression and 37 people without it, enabling 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 expanded 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 had certain symptoms of depression, with these changes also related to the severity of future symptoms.
The team added that an analysis of brain scans from 57 children who developed depression as adolescents revealed that this brain network was expanded years before their symptoms developed, while it was also expanded in adults with late-onset depression.
The researchers said this suggests that an expanded brain network may be a risk factor for developing depression, rather than a consequence of the condition.
However, they said it is unclear to what extent this enlarged network is the result of genetics or experiences, and whether the association with depression arose from this enlargement or from other brain networks that are consequently smaller.
The team added that their results could provide a way to investigate whether certain people are at greater risk of developing depression, and could help develop 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’s something identifiable in the brain that’s associated with their depression and potentially putting them at risk for their depression, I think in itself is very reassuring for some people,” he said.
Dr Miriam Klein-Flügge, from the University of Oxford, who was not involved in the work, said it was surprising that the study did not touch on the amygdala – a brain area that has been at the heart of depression research for decades.
However, she said, the new work was robust, important and exciting, adding that it raises the question of whether it is possible to reverse an extensive frontostriatal salience network with early intervention.
Klein-Flügge said further work would be needed to investigate whether the size of this network could indeed be used to predict an individual’s risk of developing depression, adding that it was unlikely to be the only useful marker to predict depression.
“But this is one useful step on the way to offering patients interventions that can be delivered on a faster timescale and that can be targeted to their individual needs,” she said.
