Specific Regions of Hippocampus Linked to Bipolar Disorder
It has been clear for some time that the volume of the hippocampus, a brain region implicated in mood and memory processing, plays a role in bipolar disorder. A 2017 article by researcher Bo Cao and colleagues in the journal Molecular Psychiatry links loss of volume in specific sub-regions of the hippocampus with bipolar disorder.
The study by Cao and colleagues used magnetic resonance imaging (MRI) and a special segmentation technique to compare the volume of certain hippocampal sub-regions across people with bipolar disorder, people with major depression, and healthy control participants.
Participants with bipolar disorder had lower volumes in subfield 4 of the cornu ammonis, two cellular layers (the granule cell layer and the molecular layer), and the tail part of the seahorse-shaped hippocampus compared to the other subjects. Participants with bipolar I disorder had particularly severe volume loss in these areas.
Cao and colleagues also found that volume loss progressed along with the illness. The volumes of the right cornu ammonis, the molecular layer, and the subiculum decreased further in patients who had bipolar disorder for longer. As manic episodes increased, the volume of both sides of the cornu ammonis and the hippocampal tail decreased.