Enlarged hypothalamus linked to depression and bipolar disorder
Over the past decade, significant progress has been made in discovering and understanding the biological processes that can make a person more at risk for depression and bipolar disorder.
In particular, it is clear that those most predisposed to developing depression show a distinct issue with regulating the endogenous stress response system, referred to as the HPA axis. In a healthy person, this system is typically triggered when confronting dangerous or stressful situation, releasing cortisol to help energize the body to deal with threats.
In a person predisposed to depression, however, the system is often triggered even when there is no threat or stressful situation present.
Why this dysregulation occurs in those at increased risk for depression has remained a mystery to researchers until this month. Now, a team of researchers from the Max Planck Institute for Human Cognitive and Brain Sciences and the Department of Psychiatry and Psychotherapy of the University Clinic in Germany say they have found evidence that people with an affective disorder (such as, but not limited to, depression) have a left hypothalamus that is an average of 5% larger than healthy individuals.
The team believes the oversized hypothalamus is likely the culprit behind the over-functioning stress response mechanism.
Not only were those with depression or bipolar disorder likely to show an enlarged hypothalamus, but the researchers also say that those with more severe symptomology showed the largest hypothalamus regardless of whether the individual was taking medications.
“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,” wrote Stephanie Schindler in the journal Psychiatrica Scandinavica. Schindler is a Ph.D. student at both research institutes involved in the study and first author of the study.
To determine the size of the hypothalamus and assess the participants’ symptomology, the participants underwent high-resolution 7 Tesla MRI imaging as well as completing standardized mental health assessments.
The findings could potentially lead to a significantly more comprehensive understanding of how depression and bipolar disorder develop, but more work will have to be done to confirm the researchers’ belief that an oversized hypothalamus could trigger affective disorders. Currently, it is impossible to say with certainty exactly what role the hypothalamus plays in the disorders.
“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.