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A new study shows that patients with depression have unexpected habenula activity, something that researchers did not expect when the study was designed and started. University College of London researchers used high-resolution functional magnetic resonance imaging (fMRI) to study habenula activity in the brains of study participants, some with depression and some without this condition. Professor Jonathan Roiser was the senior study author, and he explained “A prominent theory has suggested that a hyperactive habenula drives symptoms in people with depression: we set out to test that hypothesis. Surprisingly, we saw the exact opposite of what we predicted. In people with depression, habenula activity actually decreased when they thought they would get a shock. This shows that in depressed people the habenula reacts in a fundamentally different way. Although we still don’t know how or why this happens, it’s clear that the theory needs a rethink.”

The study on depression and habenula activity showed that there was no difference in the size of this brain region between those with depression and study participants who had never been depressed. According to Dr. Rebecca Lawson, the lead study author, “The habenula’s role in depression is clearly much more complex than previously thought. From this experimental fMRI study we can draw conclusions about the effects of anticipated shocks on habenula activation in depressed individuals compared with healthy volunteers. We can only speculate as to how this deactivation is linked to symptoms, but it could be that this ancient part of the brain actually plays a protective role against depression. Animal experiments have shown that stimulating the habenula leads to avoidance, and it is possible that this occurs for mental as well as physical negative events. So one possible explanation is that the habenula may help us to avoid dwelling on unpleasant thoughts or memories, and when this is disrupted you get the excessive negative focus that is common in depression.”