• Expanded frontostriatal salience network could be risk factor for developing condition

Researchers have gained new insight into how and why some people experience depression after finding that 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 a co-author of the research from Weill Cornell Medicine in New York, United States, Dr. Charles Lynch. He added that the expansion meant the size of other, often neighbouring, brain networks, was 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 functional magnetic resonance imaging (fMRI) scans from 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 73% on average in participants with depression compared with the 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 that 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 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 that this suggested that an expanded brain network could be a risk factor for developing depression, rather than a consequence of the condition. However, they said that it was unclear as 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, another author from Weill Cornell Medicine, Prof. Conor Liston said that 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 the risk for their depression, 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 that it was surprising that the study did not touch on the amygdala – a brain area at the core of depression research for decades. However, she said that the new work raised the question of whether it is possible to reverse an expanded frontostriatal salience network with early intervention. Klein-Flügge said that 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 that 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.

(The Guardian)