A new study found that a volume decrease in certain parts of the hippocampus, a brain region known for mood and memory processing, is linked to bipolar disorder. The findings are published in the journal Molecular Psychiatry.
“Our study is one of the first to locate possible damage of bipolar disorder in specific subfields within the hippocampus,” said Bo Cao, Ph.D., first and corresponding author and a postdoctoral fellow in the Department of Psychiatry and Behavioral Sciences at McGovern Medical School at the University of Texas Health Science Center at Houston (UTHealth).
“This is something that researchers have been trying to answer. The theory was that different subfields of the hippocampus may have different functions and may be affected differently in different mood disorders, such as bipolar disorder and major depression disorder.”
It is estimated that approximately six million Americans suffer from bipolar disorder. Bipolar I disorder is characterized by mood changes that can swing from a high-energy, manic state to a low-energy, depressive state. Patients with bipolar II disorder do not experience the full-blown manic episodes, but may have a less severe high-energy state.
The disorder can interfere with a person’s ability to work and perform daily living activities, sleep, think clearly and could lead to suicide attempts.
Cao hopes the study will pave the way for more research that specifically investigates details in the hippocampus as markers for bipolar disorder. He believes this may lead to the development of better methods for diagnosis as well as more effective treatments.
For the study, the research team used a combination of magnetic resonance imaging (MRI) and a unique segmentation approach to discover differences in the volumes of subfields of the hippocampus, a seahorse-shaped region in the brain. Participants with bipolar disorder were compared to both healthy participants as well as those with major depressive disorder.
The findings revealed that people with bipolar disorder had reduced volumes in specific areas of the hippocampus: subfield four of the cornu ammonis (CA), two cellular layers and the tail portion of the hippocampus. The reduction was more profound in subjects with bipolar I disorder than it was in the other mood disorders investigated.
Further, as the illness worsened in patients with bipolar I disorder, the volumes of certain areas in the hippocampus decreased, including the right CA 1. Volumes of other CA areas and the hippocampal tail were more reduced in the brains of people who experienced more manic episodes.