If you’re a regular reader of Cordula’s Web, chances are high that you’re also experiencing more or less severe forms of depression, and seeking solace and a quiet place. Whatever the causes (PTSD, a broken heart, mourning, burnout, …), you probably realize that those are just psychological triggers. So what are the real physiological root causes of depression?
As if dwelling in the dark hole of despair wasn’t painful enough already, society, mental health therapists, and counselors often add insult to injury by insinuating that depression were some kind of mental health problem. Since pronounced feelings of guilt are among typical symptoms of depression, this only exacerbates the anguish by inducing unnecessary shame and additional self-loathing. But what if depression was actually a natural reaction, and quite useful for the survival of the species?
That’s exactly the question that scientists Paul W. Andrews and J. Anderson Thomson, Jr. rose in a paper published in Psychological Review 116(3), 620-654 with the title “The bright side of being blue: Depression as an adaptation for analyzing complex problems” (draft here). This paper has been showcased and explained to the general public by the authors in a three page Scientific American blog post titled Depression’s evolutionary roots.
Basically, the authors report that one physiological cause of depression may be the prevalence of 5-HT1A receptors in the brain of depressed animals. Since 5-HT1A binds to serotonin, they effectively reduce the amount of serotonin available to other receptors, thus inducing the typical depression symptoms. To quote the blog post:
One reason to suspect that depression is an adaptation, not a malfunction, comes from research into a molecule in the brain known as the 5HT1A receptor. The 5HT1A receptor binds to serotonin, another brain molecule that is highly implicated in depression and is the target of most current antidepressant medications. Rodents lacking this receptor show fewer depressive symptoms in response to stress, which suggests that it is somehow involved in promoting depression.
That may explain how depression works under the hood, but it doesn’t yet tell us why it is important from an evolutionary perspective. And this is where it gets interesting:
When scientists have compared the composition of the functional part rat 5HT1A receptor to that of humans, it is 99 percent similar, which suggests that it is so important that natural selection has preserved it. The ability to “turn on” depression would seem to be important, then, not an accident.
If evolution preserved the molecular trigger that causes depression, then for some good reason. There’s one common behavior among us depressed people: we tend to think intensely about complex problems. These ruminations are characterized by the fact that the brain needs to isolate itself from surrounding stimuli for extended periods of time so as not to be distracted. And this is where depression comes into play.
Psychologically, a depressed person tends to ignore external stimuli, because she cares less about her surroundings. But this is just the symptom. Physiologically, there’s a region in the brain, called ventrolateral prefrontal cortex (VLPFC) that is responsible for enabling concentrated thinking. The neurons in this region have to fire continuously during those periods of rumination. This task is very energy consuming. Moreover, continuously firing neurons eventually break down and temporarily cease to function. So there are obviously built-in limits to ruminations: one has to go back to real life instead of brooding, right?
But how can depressed people extend the period of time they dedicate to intense thinking? This is where 5-HT1A receptors come into play. Those receptors not only prevent the VLPFC neurons from breaking down, they also provide them with the additional energy necessary for them to sustain the firing mode over extended periods of time.
From an evolutionary perspective, depression isn’t the obstacle to but rather the enabler of deep thinking!
The authors come to the following conclusion:
But depression is nature’s way of telling you that you’ve got complex social problems that the mind is intent on solving. Therapies should try to encourage depressive rumination rather than try to stop it, and they should focus on trying to help people solve the problems that trigger their bouts of depression.
So next time someone tries to make you feel bad about you’re being depressed, just remember: this isn’t an illness to be ashamed of. Rather than that, it is a natural reaction, and it is necessary for the survival of our species. Let’s be proud of it, we’re in good company.
May 31st, 2010 at 5:06 pm
Just want to say what a great blog you got here!
I’ve been around for quite a lot of time, but finally decided to show my appreciation of your work!
Thumbs up, and keep it going!
Cheers,
Christian.