A new analysis, led by Janine Bijsterbosch at Washington University School of Medicine in St Louis, Missouri, involving more than 23,000 brain scans, has reportedly surprised researchers by revealing that depression does not, in fact, shrink the hippocampus, the brain’s primary memory center. This finding challenges a decade-long understanding, including a 2015 study of nearly 9000 people which concluded that recurrent depression led to smaller hippocampi. Bijsterbosch's team utilized modern imaging techniques, unavailable in 2015, across six large-scale datasets, including the UK Biobank.
The researchers were reportedly surprised to find no significant link between depression, assessed via questionnaires, and hippocampal volume. John Fleming, from Southern Colorado TMS Center, affirmed this finding. He emphasized the study's importance, suggesting a need to learn more about all brain regions and not “take hippocampal shrinkage as a given.”
Instead of the hippocampus, the team linked depression to reduced grey matter volume or cortical surface area in three distinct regions: the frontal cortex, the anterior cingulate, and the insula. These areas are critically involved in emotional regulation. Specifically, the frontal cortex governs judgment and self-control, the anterior cingulate impacts decision-making and motivation, and the insula aids in perceiving pain. Fleming observed that “all of these [traits and conditions] are disrupted in depressive symptoms,” positing that these reduced volumes may help account for common depressive manifestations such as brain fog and pain.
Bijsterbosch acknowledged that her team measured depression at a single time point, unlike previous research that tracked multiple episodes. She also noted that most participants in the study experienced mild to moderate symptoms, suggesting hippocampal shrinkage might still occur in recurrent or severe cases. Fleming suggested that if the effects of depression on the brain are further explored, it could inform understanding of the link between the mental health condition and dementia, noting a larger brain can protect against cognitive decline. He mentioned the potential for transcranial magnetic stimulation to increase brain volume, if future research robustly links shrinkage to depression.
Bijsterbosch concluded that a clearer understanding of depression's brain basis could “inform future work to understand individual differences and ultimately guide improvements in personalised treatment.” Researchers anticipate future studies will explore if feeling good corresponds with brain regions responsible for not feeling terrible.
