A new study reveals that in people who are depressed or have bipolar disorder, the left hypothalamus was on average 5 percent larger than that of their healthy counterparts.
It has long been known that people more predisposed to depression show a dysregulation of the endogenous stress response system, otherwise known as the hypothalamic-pituitary-adrenal axis (HPA axis), which is normally triggered when we are faced with a stressful situation.
This response increases the amount of cortisol, providing the body with more energy when faced with a potential threat or challenge. Once the challenging situation has passed, several control mechanisms in the HPA axis normally ensure the system returns to a balanced state, researchers explain.
But for people who suffer with depression or who are more predisposed, this is not the case. Instead, a malfunction of the feedback mechanism results in a stress response operating at full throttle, even when there is no apparent stressful situation, according to the researchers.
Until now, the underlying reason for this hyperactive stress response system and the role of the hypothalamus as its overall control unit has remained unclear.
In a recent study with 84 participants, scientists at the Max Planck Institute for Human Cognitive and Brain Sciences and the Department of Psychiatry and Psychotherapy of the University Clinic in Germany discovered that in people with an affective disorder, the left hypothalamus was on average 5 percent larger than that of their healthy counterparts.
“We observed that this brain region is enlarged in people with depression, as well as in those with bipolar disorder, two types of affective disorders,” said Stephanie Schindler, a PhD student at both research institutes involved in the study and first author of the study, which was published in the scientific journal Acta Psychiatrica Scandinavica.
The scientists also found that more severe the depression, the larger the hypothalamus was. Medication did not have any effect on the size of the hypothalamus, they added.
For the study, the researchers used a high-resolution 7-Tesla MRI scanner on the study participants. The severity of disorders was measured using standardized questionnaires and interviews, according to the researchers.
Although studies have shown this brain structure to be more active in people with depression or bipolar disorder, it is not yet known what role a larger hypothalamus plays, the researchers add.
“Higher activity could lead to structural changes and thus to a larger volume of the hypothalamus normally the size of a one cent coin,” said Dr. Stefan Geyer, one of the study’s principal investigators and head of the research group Anatomical Analysis of the Organization of the Human and Non-Human Primate Brain at the Max Planck Institute for Human Cognitive and Brain Sciences.