322 million people in the world are affected by depression, which represents no less than 4.4% of the world's population. By noting, in depression, that the area of the brain dedicated to controlling stress is more voluminous, this team from the Max Planck Institute, identifies a new diagnostic marker for depression but also encourages us to better understand why this cerebral structure is more active in people with depression or bipolar disorder.
In these depressed patients, the areas of the hypothalamus (in red on the visual) are more developed than in their healthy counterparts. The researchers suggest that this "hypertrophy" could result either from a predisposition or from exposure to environmental stressors. We already knew that people more predisposed to depression have a dysregulation of the endogenous stress response system or hypothalamic-pituitary-adrenal axis.(HPA axis), which is normally triggered in the event of a stressful situation. This response increases cortisol levels, providing the body with more energy when faced with a threat or challenge. Once the difficult situation has passed, several control mechanisms of the HPA axis normally guarantee a return to equilibrium of the system.
Malfunction of the HPA axis feedback mechanism: In people with a depressive disorder or predisposed to depression, this is not the case. The dysfunction of the feedback mechanism results in a stress response operating at full speed, even in the absence of apparent stress. Until now, the underlying reason for this overactive stress response system and the role of the hypothalamus in this process remained poorly understood. The study conducted using a high-resolution MRI scanner with 84 participants reveals that:
- the left hypothalamus is on average 5% higher in depressed patients vs their healthy counterparts;
- this observation is also made in patients suffering from bipolar disorder;
- finally, in a group of participants suffering from depression, the more severe the depression, the more the hypothalamus is enlarged;
- finally, antidepressant treatments had no effect on the size of the hypothalamus.
Although previous studies have shown that this brain structure is more active in people with depression or bipolar disorder, it is not yet clear what role this larger hypothalamus plays.
The researchers here suggest that its higher activity in these patients could mechanically lead to structural changes and therefore greater volume. Anyway it is an interesting marker for the detection of depression.
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