The left side of the hypothalamus was revealed to be 5 percent larger in a new study of people with affective disorders such as depression and bipolar.
Functional MRI and other new imaging techniques have allowed researchers to locate several brain areas and networks that are at play in affective disorders. For instance, in the case of depression, studies have found treatment-resistant depression is associated with decreased hippocampal volume and a smaller amygdala.
The hippocampus is a region area heavily involved in memory formation and learning, whereas the amygdala is a small brain structure involved in emotional processing and the response to what is perceived as danger or stress.
In fact, the entire endocrine stress response system, or “HPA-axis,” is disrupted in people who have depression. The axis between the hypothalamus, the pituitary gland, and the adrenal glands is overactive, which previous research established as a “core neurobiological feature of major depression.”
Normally, the HPA-axis raises levels of the stress hormone cortisol to ensure that the body is better equipped to handle a situation perceived as dangerous or threatening.
After the threat passes, the HPA-axis is also responsible for lowering cortisol and diminishing other stress responses back to normal levels.
However, in the case of individuals with depression, these structures are in “overdrive” even in the absence of objective danger. New research aimed to clarify the role of the hypothalamus in this hyperactive chain reaction.
They used MRI to study the participants’ brains and high‐precision volumetry to determine the size of their hypothalami.
Overall, they saw that people with an affective disorder had a 5 percent increase in the volume of the left side of their hypothalamus, on average.
“We observed that this brain region [the hypothalamus] is enlarged in people with depression as well as in those with bipolar disorder, two types of affective disorders.”
Importantly, in the case of people with depression, hypothalamus size correlated directly with the severity of the condition.
Medication did not affect the size of the brain region. The researchers warn that beyond the links they found, not much can be inferred on the causality underlying the findings.
“Higher activity could lead to structural changes and thus to a larger volume of the hypothalamus normally the size of a one-cent coin,” explains study co-author Stefan Geyer.
The authors write, “Supported by emerging evidence that the stress response may be related to structural and functional asymmetry in the brain, our finding suggests a crucial role of the hypothalamus in mood disorders.”