Depression leaves its imprint on the brain

Depression, a common mood disorder that causes a persistent feeling of sadness, affects one in 20 Indians. Unlike most other health conditions, there are no clinical diagnostic tests, like blood tests or scans, for doctors to look at and diagnose depression. Instead, they rely on subjective questionnaires that try to understand an individual’s self-reported mood changes over time. But that could soon change for the better with a new neurological discovery of depression ‘signatures’ in the brain. 

In the biggest neurological study of its kind, scientists used functional Magnetic Resonance Imaging (fMRI)—an imaging technique that lets them study the brain’s neurons and measure the synapses that pass through the nerve cells—over a period of time in people with and without depression. Then, they compared brain scans to spot the differences, not only between individuals diagnosed with the condition and those who were not, but also between an individual’s growing adolescent brain before the depression diagnosis and the adult brain after the diagnosis. 

The scans revealed a remarkable ‘biomarker’ or ‘signature’. The brains of individuals who were diagnosed with depression showed a marked increase in a part of the brain called the salience network, which has a bunch of neurons involved in switching the brain between creating working memory and being internally aware and helps the brain decide which of the external stimuli and internal emotions it needs to respond to. The salience network in the brains of people with depression was twice as large. This increase appeared much before the person was diagnosed with depression and persisted even when the person was not currently depressed.

While the scientists are yet to figure out what causes the enlargement, they believe their findings point to an ‘early warning system’ in the brain for depression. This first-ever biomarker of a permanent change in the brain’s network can, someday, help identify who is at risk of developing depression and needs intervention through therapy, much before symptoms begin to show up.