Depression and the shrinking seahorses in the brain

Seahorses are beautiful creatures. The biologists convince us that seahorses are fish, even if they don’t look anything like fish. They also tell us, intriguingly, that seahorses are monogamous and the males do the childbearing.

By © Hans Hillewaert, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=22106851
By © Hans Hillewaert, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=22106851

But why is a neurologist talking about seahorses. It’s all in the name. The Latin name for seahorse is hippocampus , derived from hippos for horse, and kampos for sea monster. Where biologists saw fish, the ancients saw monsters. And you really can’t blame them…take a closer look

By Gervais et Boulart - Les poissons Gervais, H., Public Domain, https://commons.wikimedia.org/w/index.php?curid=19157222
By Gervais et Boulart – Les poissons Gervais, H., Public Domain, https://commons.wikimedia.org/w/index.php?curid=19157222

Deep in the brain is a structure also called the hippocampus, one on each side. The hippocampus plays a central role in memory, and it is considered by some to be the brain’s emotional centre.

By Images are generated by Life Science Databases(LSDB). - from Anatomography, website maintained by Life Science Databases(LSDB).You can get this image through URL below. 次のアドレスからこのファイルで使用している画像を取得できますURL., CC BY-SA 2.1 jp, https://commons.wikimedia.org/w/index.php?curid=7887124
By Images are generated by Life Science Databases(LSDB). – from Anatomography, website maintained by Life Science Databases(LSDB).You can get this image through URL below. 次のアドレスからこのファイルで使用している画像を取得できますURL., CC BY-SA 2.1 jp, https://commons.wikimedia.org/w/index.php?curid=7887124

It is no mystery why neuroanatomists name this important part of the brain after the seahorse, the resemblance is eerily striking.

By Hippocampus_and_seahorse.JPG: Professor Laszlo Seressderivative work: Anthonyhcole (talk) - Hippocampus_and_seahorse.JPG, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9451294
By Hippocampus_and_seahorse.JPG: Professor Laszlo Seressderivative work: Anthonyhcole (talk) – Hippocampus_and_seahorse.JPG, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9451294

Neurologists are passionate about the hippocampus for various reasons. In people with memory complaints, for example, hippocampal atrophy may predict the development of Alzheimer’s disease . A shrunken hippocampus is also seen in some forms of epilepsy. Neurologists therefore endlessly harangue their neuroradiology colleagues to look closely at their patients’ brain MRI scans, and to tell them that the hippocampus is shrunken…even if it’s just a little bit smaller. Unfortunately for the neuroradiologists, the MRI scans do not come colour-coded as in the illustrative scan below.

By Amber Rieder, Jenna Traynor - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=16393748
By Amber Rieder, Jenna Traynor – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=16393748

This blog post is however about major depression, and not about epilepsy or dementia. Depression, that bad feeling we all feel every now and then is frustrating, but major depression is devastating. And we now know that it is accompanied by major alterations in the structure of the brain. And, yes, the changes are in the hippocampus. I got interested in this subject when I came across a piece in Neurology News reporting that people with depression have a smaller hippocampus. 

depression-242024_1280

The association of depression with hippocampal atrophy is however an old one. Proceedings of the National Academy of Science (PNAS) reviewed the relationship in an editorial from 2011 titled Depression, antidepressants, and the shrinking hippocampus. The author addressed the unresolved puzzle…which of the two came first. Reminiscent of the chicken and egg scenario, it is not clear if the hippocampal atrophy causes depression, or vice versa. To add to the puzzle, the paper conjectured the possibility of a third, unknown agent, causing both the depression and the small hippocampus.

Depression. Shattered.art66 on Flikr. https://www.flickr.com/photos/shattered_art/3369289879
Depression. Shattered.art66 on Flikr. https://www.flickr.com/photos/shattered_art/3369289879

This question was the focus of a meta-analysis published in Molecular Psychiatry this year. It reviewed the brain imaging data of 15 studies, involving about 1700 people with major depression. Titled Subcortical brain alterations in major depressive disorder, the authors confirmed the link between depression and hippocampal atrophy, and also showed that the shrinkage is worse in those who developed depression at an early age, and in those who have had frequent episodes of depression.

5 stages of grief (Depression) #4. COCOMARIPOSA on Flikr. https://www.flickr.com/photos/8463160@N08/1790592784
5 stages of grief (Depression) #4. COCOMARIPOSA on Flikr. https://www.flickr.com/photos/8463160@N08/1790592784

Does depression lead to hippocampal atrophy? The meta-analyses hinted so, but there were too many caveats for the authors to arrive at a definitive conclusion. They admit that more needs to be done to unravel depression….leaving the mystery of the shrinking seahorses to continue to another day.

 

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