A general theory of mental illness
Back when I was attending classes to help me cope with depression, one of the most surprising things I learned was just how common mental illness really is. According to one study of 9,000 people in the US, depression affects somewhere between 15–17% of the population — and that’s just depression, sometimes called the “common cold” of mental illness due to its frequency. We’re not even considering the numerous other illnesses recognized by psychiatry, from anorexia to schizophrenia.
While I do think it’s strange that we don’t readily talk about something affecting so many people, that’s not the point I want to make here. I’m interested in trying to figure out why mental illness is so common.
After mulling it over for a while, I came up with a conceptual theory, and I’m curious what others think of it: Perhaps the prevalence of mental illness is an inevitable consequence of having an extraordinarily complex brain.
To describe this theory, I want to use an analogy to machinery. First, let’s consider simple machines. There are six of them: Screw, wedge, inclined plane, pulley, lever, and wheel and axle. Their function is, well, simple. They change the direction or strength of a force.
Now let’s contrast simple machines with something more complex. One example I like to think of is the automobile, since it’s a complicated machine most of us interact with on a regular basis. I don’t know a whole lot about how cars work, so if I’m oversimplifying or misunderstanding, please forgive me!
Conceptually, an automobile is numerous subsystems — such as engine, transmission, steering, and so forth (and you could subdivide those even further if you want) — working in concert to move people and cargo from one place to another. Ideally, the entire system does so safely, comfortably, and maybe even stylishly!
Each subsystem itself is composed of numerous simple machines. After all, a mere screw qualifies as a simple machine, and imagine how many of those go into a typical car! My point here is, for a car to operate as intended, hundreds of simple machines need to be in the right places at the right times, and they must work properly. If any one of those simple machines isn’t working right, the car as an entire system will exhibit unexpected behavior.
That’s not to say the car will necessarily stop functioning entirely. You might end up with something more along the lines of an inconvenience: Perhaps the door locks won’t close at the mere push of a button, or you won’t be able to stay cool on a hot day with the luxury of air conditioning. It’s annoying, yes, but provided the engine and such are OK, the car’s core function remains intact. It can still get people and stuff from point A to point B.
To summarize, complicated machinery has all sorts of failure modes, and the manifestation of failure isn’t a simple binary working/not working; rather, there’s a spectrum of function. Even if minor things go wrong, the machine as a whole might still be able to keep going, but the effectiveness or quality of experience will be impaired. It’s only when critical components break do you end up with complete failure to function.
With that thought in mind, let’s turn the discussion to brains. Experts in neurology believe our brains, composed of billions of neurons — cells that process and transmit information through electrochemical signals — are one of the most complicated structures in the known universe. We still have a poor understanding of how our brains even work, but they’re certainly way more complicated than any car!
Somewhat analogous to a car, different parts of the brain handle different functions. Exactly what those sections are and what they do is far beyond my understanding, but for one to do the things we consider uniquely human— planning, generalizing, and so forth — all the subsystems have to work together.
As you would expect with an enormously complicated organ, there are plenty of things that can go wrong with our brains. While they do exhibit a surprising ability to recover from trauma by “rerouting” around damage — a fascinating phenomenon called neuroplasticity — there’s only so much stuff in our skulls to work with. Sufficient disturbance can still impair the brain’s ability to keep everything chugging along.
For one specific example, research cited by well-known neurologist and author Robert Sapolsky regarding the pathology of depression suggests damage to a part of the brain called the hippocampus is related (and incidentally, this also purports to explain some of the symptoms associated with depression, such as memory loss and decreased cognitive ability).
When neurologists performed MRI scans of a handful of brains, including some from people with histories of chronic depression, they found that the volumes of the hippocampi were significantly smaller in those who had suffered from depression. Why might that be?
My understanding is the exact mechanism behind this change in hippocampal volume is still unclear, but there is a theory: Being under stress releases certain hormones — cortisol, secreted by the adrenal gland, is the main suspect here — which destroy certain cells in the hippocampus with prolonged exposure. On the bright side, the damage is somewhat reversible in time, provided the stress hormones stop pouring into the brain. Certain antidepressants appear to help accomplish that.
Similar to how a car with, say, a broken air conditioner can still transport you places, a brain with a damaged hippocampus doesn’t cease functioning entirely. A person suffering from depression can still think, reason, generalize, plan, and so on, but quality of life is undoubtedly diminished.
Think about it this way: You can drive a Depression™ brand car, but the experience is miserable. The radio constantly screams, “You’re worthless!” and you can’t shut it off. The car will get you where you need to go, but you won’t be happy about it.
I haven’t read anything about the pathology of other mental illnesses, but I don’t think it would be completely outrageous to suggest different conditions stem from damage to different parts of the brain. Maybe if you mangle the medulla, you end up with mania, or if you sever the cerebellum, you get cyclothymia.
At first blush, it might seem strange that mental illness would be so common, but if you think about our brains as analogous to some kind of machine, it makes a lot more sense. Complicated machines can be damaged and still technically function, although they may not perform as well as would otherwise be expected; I think such is the case with our brains, too. Mental illness arises from damage to the complex contraptions in our crania.