Researchers have gained new insight into how and why some people experience depression after finding a particular brain network is far bigger in people living with the condition. The surface of the brain is a communication junction box at which different areas talk to each other to carry out particular processes. But there is a finite 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’s taking up more real estate on the brain surface than 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 meant the size of other – often neighbouring – brain networks were smaller. Writing in the journal Nature, Lynch and colleagues report how they used precision functional mapping, a new approach to brain imaging that analyses a host of fMRI (functional MRI) scans from each individual. The team applied this method to 141 people with depression and 37 people without it, enabling them to measure accurately 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 73% on average in participants with depression compared with 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 synchronised when participants had certain symptoms of depression, with these changes also associated with the severity of future symptoms. The team added that an analysis of brain scans from 57 children who went on to develop depression as adolescents revealed 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 suggested an expanded brain network could be a risk factor for developing depression, rather than a consequence of the condition. However, they said it was unclear to what extent this enlarged network was the result of genetics or experiences, and whether the association with depression arose from this expansion or from other brain networks consequently being smaller. The team added that their results could offer a way to explore whether certain people may be at increased risk of developing depression, and could help develop personalised treatments. But Prof Conor Liston, another author from Weill Cornell Medicine, said the results could benefit people with depression more widely. “Having that information, that there’s something identifiable in the brain that is associated with their depression and may be conferring risk for their depression, I think is, by itself, really reassuring for some people,” he said. Dr Miriam Klein-Flügge, of the University of Oxford, who was not involved in the work, said it was surprising the study did not touch on the amygdala – a brain area at the core of depression research for decades. However, she said, the new work was robust, important and exciting, adding it raised the question of whether it was possible to reverse an expanded frontostriatal salience network with early intervention. Klein-Flügge said further work would be needed to explore whether the size of this network could indeed be used to predict an individual’s risk of developing depression, adding it was unlikely to be the only helpful marker for predicting depression. “But it is one useful step on the road towards offering patients interventions that can be delivered at a faster timescale and that can be targeted to their individual needs,” she said.