After years of controversy among researchers, the results finally determined that persistent depression causes brain damage, and not the other way around.
Neurologists previously had hypothesized that brain damage was a predisposing factor for chronic depression, but a new study published in Molecular Psychiatry sheds a different light on the subject.
The study, which consisted of 9,000 individual samples, collected from the ENIGMA group, succeeded in definitively proving a causal relationship between persistent depression and brain damage. Magnetic resonance images (MRIs) showed evidence of shrinkage of hippocampus in 1,728 patients diagnosed with chronic depression compared to the 7,199 healthy individuals who participated in the study.
Specifically, the study found that those patients diagnosed with major depressive disorder, “showed robust reductions in hippocampal volume (1.24%) in MDD(Major Depressive Disorder) patients compared with healthy controls.”
What is the hippocampus?
The hippocampus is a small area of the brain that is located in the medial temporal lobe of the brain. It is comprised of two halves, one which resides on each hemisphere of the brain. It plays an important role in the limbic system.
The main functionality of the hippocampus encompasses the creation of new memories, the formation of long term memory, and spatial navigation. It also plays a significant role in storage and of new memories and associating emotions to these memories.
Inside the hippocampus resides the amygdala. This part of the brain plays the most crucial part in the processing of emotions, comprehending emotional expressions in others and also connecting emotions to certain memories. Amygdala forms a part of the limbic system too.
Amygdala was previously linked with depression. Studies in the past have suggested a direct relationship between a shrinkage in the hippocampus and depression, but the sample size of previous studies hasn’t been large enough to yield reliable results.
The hippocampus and depression
Researchers have found that in addition to its importance in forming and maintaining memories, the hippocampus is also pivotal in controlling emotions. Professor Ian Hickie, a co-author of the study and a renowned mental health campaigner, explains the hippocampus’ relationship to depression, “Your whole sense of self depends on continuously understanding who you are in the world – your state of memory is not about just knowing how to do Sudoku or remembering your password – it’s the whole concept we hold of ourselves”
Professor Hickie further elaborates on the relationship between a shrinkage in the hippocampus and changes in behavior observed in animals from the past, “We’ve seen in a lot of other animal experiments that when you shrink the hippocampus, you don’t just change memory, you change all sorts of other behaviors associated with that – so shrinkage is associated with a loss of function.”
Those who suffer from depression usually have low self-esteem and lack of motivation in completing even day to day self-care activities like bathing, eating, combing one’s hair or dressing. It is common for those suffering from depression to also have a deflated self-confidence, which simply refers to their negatively distorted self-image.
This could potentially affect how one forms memories, and how they view themselves in the past and thus project themselves in the future.