New Research Reveals A Brain Network That's Larger In People With Depression

This single part of the brain is over twice as large in people with depressive disorders. Here's how it was discovered.

By Mark Travers, Ph.D. | November 07, 2024

For many years, psychological research regarding the depressed brain often overlooked individual differences, relying heavily instead on group averages. Most often, these studies took a "snapshot" approach; they captured brain activity at a single point in time, without follow-ups or comparisons.

While this one-size-fits-all approach has taught us much about depression, it lacks the depth necessary to capture its highly varied nature. However, a September 2024 study from Nature has addressed this gap in literature—and its results are incredible.

Here's how researchers Charles Lynch and Conor Liston discovered an entire brain network that was doubled in size in individuals with depression—namely, the "salience network"—and what it means for those who suffer with it.

The "Salience Network" Is Twice As Large In Individuals With Depression

"Depression is an episodic condition, meaning symptoms come and go over time," explains Lynch in an interview with PsyPost. He continues, "However, most brain imaging studies to date acquire a single brain scan at one point in time (a cross-sectional approach)."

Thus, by means of fMRI scans, Lynch and Liston took a unique approach to researching the link between neurology and depression. Specifically, they focused on blood flow changes, as these are capable of revealing real-time patterns of brain activity. Additionally, they focused on these changes at the individual level, as opposed to averaging findings across groups—allowing for a unique fingerprint-like map of each participant's brain.

After scanning six participants with a formal diagnosis of major depressive disorder (MDD)—along with 37 healthy individuals with no prior mental health conditions in the control group—Lynch and Liston managed to capture changes and patterns in the brain that developed gradually. Across 22 separate sessions, they scanned participants for around 621.5 minutes ( around 10 hours), providing them ample imagery of each brain.

Their most pertinent finding was, in four of the six depressed individuals, that the salience network was over double the size of those in the healthy control group. This enlargement was most prominent in brain regions associated with emotional and cognitive processing—specifically ones that are well known to play a role in how people process emotions and assess rewarding or meaningful experiences.

The extent of these expansions of the salience network were remarkable. On average, the salience network occupied approximately 73% more of the brain's outer layer—far more than the people without depression. To put this into perspective, the salience network usually covers around 3.17% of this layer in a healthy brain; in people with depression, it occupies approximately 5.49% on average.

How A Larger "Salience Network" Impacts Individuals With Depression

Lynch and Linton note that the salience network is instrumental in switching the brain between the two other key networks: the externally focused central executive network and the internally focused default mode network. This could mean that the increased size of the salience network in depressed individuals might result in dysfunctional use of the default mode network—which is linked to behaviors such as self-reflection, daydreaming, mind wandering and depressive rumination.

In simpler terms, the salience network plays a key role in filtering and prioritizing stimuli; it essentially helps the brain decide what's most important in any given moment. If it's larger in people with depression, it could mean their brains are more intensely attuned to certain internal cues—like negative thoughts, memories or emotions—and have a harder time shifting focus outward, or disengaging from them at all.

In the researchers own words, these findings greatly contribute "to understanding the brain areas and networks responsible for individuals with depression transitioning between periods of relative wellness vs. periods of severe illness, in addition to identifying features of how these brain networks are organized spatially (for example, their size) that may confer risk for depression."

The Bottom Line

Whether you're familiar with neuroscience or not, the implications of these findings could potentially make sense of a wide variety of depressive symptoms—particularly in terms of rumination and anhedonia.

Anhedonia—that is, the loss of interest or pleasure in typically enjoyable activities—often stems from an impaired ability to find things meaningful or engaging. And if the salience network is overactive, it could keep shifting the person's focus away from what's happening in the moment to their own inner dialogue. This means that even if they're doing something they used to enjoy, their mind might constantly wander—picking apart thoughts or memories rather than engaging with the pleasure of the activity.

Likely, a larger salience network could reinforce anhedonia by "locking" attention onto certain internal states—especially negative or self-critical ones, which can disrupt the brain's ability to engage with rewarding experiences.

The same goes for cycles of rumination—where the brain keeps "zooming in" on the same negative themes. With an extra-sensitive salience network, negative thoughts might feel particularly compelling; it can create an unfortunate self-reinforcing loop—one that's incredibly hard to break out of. This overactive network can become something like a magnet for negative thoughts: it keeps you locked in cycles that drain your energy and sense of pleasure over time.

Lynch and Linton's findings offer a new lens through which we can view depression, and they may bring a sense of clarity—or even relief—for individuals who experience its weight daily. Persistent negative thoughts, compounded by a lack of pleasure in once-enjoyable activities, can be unimaginably isolating and confusing; it can leave people feeling disconnected from their surroundings, as well as their very own sense of self. But knowing there may be a neurological source for these symptoms—a physical reason behind these mental experiences—can open up new ways to understand and manage them.

If you're battling depression, the next time you find yourself "stuck" on a difficult or disturbing thought, it might help to remember that this response could be the brain's way of redirecting your attention inward. Doing your best to recognize this mechanism might offer a moment of self-compassion and the courage to refocus—even if just a little—on the world around you. Over time, these little shifts in focus could help to create space for other experiences and, most importantly, for healing.

Do you often get "stuck" on disturbing or difficult thoughts? Take this science-backed test, and find out if you have a problem with rumination: Mistake Rumination Scale

A similar version of this article can also be found on Forbes.com, here.