Depression May Affect the Brain, but Its Course Matters

Depression can affect the brain, although its effects are not identical for every person.

A 10-year study indicates that the key factor may be less about whether a person has depression and more about the way the condition develops over time.

There is also a positive message: participants whose depression took a more favourable course had comparatively stable brain structure.

The results question the notion that depression unavoidably produces permanent damage. Instead, they indicate that the brain may take different routes according to how long depression continues, how frequently it recurs and how severely it affects everyday life.

Researchers in Germany tracked 206 people for as long as a decade. Of these, 57 had major depressive disorder - the clinical term for depression severe enough to substantially disrupt daily functioning - and 149 were healthy controls.

Every participant received between three and six MRI scans at intervals of roughly two years. In total, the researchers examined all 791 brain scans.

That extended timeframe is especially important.

Many brain-imaging studies of depression resemble snapshots, comparing people with and without depression at a single point. One image cannot establish whether a brain difference existed beforehand, emerged during a severe episode or gradually developed over several years.

This research, by contrast, was more like a film.

The team observed changes in each participant's brain while documenting the progression of their illness.

Depression over time and brain scans

They examined three brain areas frequently associated with depression: the hippocampus, insula and dorsolateral prefrontal cortex.

The hippocampus is involved in forming memories and processing emotions. The dorsolateral prefrontal cortex contributes to planning, decision-making, attention and emotional regulation. The insula assists the brain in making sense of emotions and signals originating within the body.

To assess depression's long-term burden, the researchers brought together four factors: the length of time each participant had lived with the condition, their number of depressive episodes, the amount of time spent depressed and how often they had been admitted to hospital.

Participants with a greater accumulated burden across the years generally experienced more rapid reductions in grey matter within the hippocampus and dorsolateral prefrontal cortex.

Grey matter includes many of the brain cells and connections used to process information. A measured change in its volume does not necessarily mean brain cells have died or that someone has experienced irreversible brain damage.

Crucially, a diagnosis of depression alone did not predict the same pattern of brain changes for everybody.

In the primary analysis, acute symptoms were significantly associated with hippocampal change, but this inconsistent pattern was not replicated.

Rather than the diagnosis or a short-term increase in symptoms, the broader course of the condition seemed to matter more.

Why depression can follow different brain paths

This could help account for the inconsistent findings from earlier research that compared groups at one time point only. Depression is not a single, uniform experience occurring in millions of brains.

Some people recover and stay well, while others have repeated episodes or live with symptoms for prolonged periods. Grouping everyone with the same diagnosis together may conceal these differing trajectories.

The study cannot establish that persistent or recurrent depression caused the observed brain changes.

It may be that pre-existing brain differences made certain participants more susceptible to a severe course. Stress, physical health, living circumstances, medication and therapy may likewise affect both depression and the brain.

The researchers accounted for participants' overall medication use, but they were unable to fully distinguish the effects of particular medicines or psychotherapy.

Study limitations and what remains unknown

The research had further limitations. The depression group was relatively small, every participant was of Western European ancestry and the study took place at a single centre.

Certain findings - especially those concerning the hippocampus - varied according to the data and statistical approaches used. A separate replication analysis delivered mixed results: the prefrontal cortex displayed a comparable pattern, but this was not statistically significant.

The changes identified were limited to small brain regions as well. Larger research projects including more diverse populations will be required to verify them.

Even so, repeatedly scanning the same individuals provides an unusually detailed picture of depression over time.

The findings do not portray a brain that is simply damaged at the point of diagnosis. They instead show several possible paths - from declining grey matter among people with a greater and more prolonged illness burden to relative stability among those with more favourable courses.

Researchers still do not know whether effective treatment can safeguard these regions or reverse the changes. However, the fact that decline was not inevitable keeps that important question open.

Depression may affect the brain, but this study indicates that the outcome is not determined at diagnosis.

The study appeared in JAMA Network Open.

This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. Although we take pride in our process, we are only human. If you notice an error, please let us know.