Mental illness is different from physical illness.

Post 311 Oct 13 JDN 2458770

There’s something I have heard a lot of people say about mental illness that is obviously well-intentioned, but ultimately misguided: “Mental illness is just like physical illness.”

Sometimes they say it explicitly in those terms. Other times they make analogies, like “If you wouldn’t shame someone with diabetes for using insulin, why shame someone with depression for using SSRIs?”

Yet I don’t think this line of argument will ever meaningfully reduce the stigma surrounding mental illness, because, well, it’s obviously not true.

There are some characteristics of mental illness that are analogous to physical illness—but there are some that really are quite different. And these are not just superficial differences, the way that pancreatic disease is different from liver disease. No one would say that liver cancer is exactly the same as pancreatic cancer; but they’re both obviously of the same basic category. There are differences between physical and mental illness which are both obvious, and fundamental.

Here’s the biggest one: Talk therapy works on mental illness.

You can’t talk yourself out of diabetes. You can’t talk yourself out of myocardial infarct. You can’t even talk yourself out of migraine (though I’ll get back to that one in a little bit). But you can, in a very important sense, talk yourself out of depression.

In fact, talk therapy is one of the most effective treatments for most mental disorders. Cognitive behavioral therapy for depression is on its own as effective as most antidepressants (with far fewer harmful side effects), and the two combined are clearly more effective than either alone. Talk therapy is as effective as medication on bipolar disorder, and considerably better on social anxiety disorder.

To be clear: Talk therapy is not just people telling you to cheer up, or saying it’s “all in your head”, or suggesting that you get more exercise or eat some chocolate. Nor does it consist of you ruminating by yourself and trying to talk yourself out of your disorder. Cognitive behavioral therapy is a very complex, sophisticated series of techniques that require years of expert training to master. Yet, at its core, cognitive therapy really is just a very sophisticated form of talking.

The fact that mental disorders can be so strongly affected by talk therapy shows that there really is an important sense in which mental disorders are “all in your head”, and not just the trivial way that an axe wound or even a migraine is all in your head. It isn’t just the fact that it is physically located in your brain that makes a mental disorder different; it’s something deeper than that.

Here’s the best analogy I can come up with: Physical illness is hardware. Mental illness is software.

If a computer breaks after being dropped on the floor, that’s like an axe wound: An obvious, traumatic source of physical damage that is an unambiguous cause of the failure.

If a computer’s CPU starts overheating, that’s like a physical illness, like diabetes: There may be no particular traumatic cause, or even any clear cause at all, but there is obviously something physically wrong that needs physical intervention to correct.

But if a computer is suffering glitches and showing error messages when it tries to run particular programs, that is like mental illness: Something is wrong not on the low-level hardware, but on the high-level software.

These different types of problem require different types of solutions. If your CPU is overheating, you might want to see about replacing your cooling fan or your heat sink. But if your software is glitching while your CPU is otherwise running fine, there’s no point in replacing your fan or heat sink. You need to get a programmer in there to look at the code and find out where it’s going wrong. A talk therapist is like a programmer: The words they say to you are like code scripts they’re trying to get your processor to run correctly.

Of course, our understanding of computers is vastly better than our understanding of human brains, and as a result, programmers tend to get a lot better results than psychotherapists. (Interestingly they do actually get paid about the same, though! Programmers make about 10% more on average than psychotherapists, and both are solidly within the realm of average upper-middle-class service jobs.) But the basic process is the same: Using your expert knowledge of the system, find the right set of inputs that will fix the underlying code and solve the problem. At no point do you physically intervene on the system; you could do it remotely without ever touching it—and indeed, remote talk therapy is a thing.

What about other neurological illnesses, like migraine or fibromyalgia? Well, I think these are somewhere in between. They’re definitely more physical in some sense than a mental disorder like depression. There isn’t any cognitive content to a migraine the way there is to a depressive episode. When I feel depressed or anxious, I feel depressed or anxious about something. But there’s nothing a migraine is about. To use the technical term in cognitive science, neurological disorders lack the intentionality that mental disorders generally have. “What are you depressed about?” is a question you usually can answer. “What are you migrained about?” generally isn’t.

But like mental disorders, neurological disorders are directly linked to the functioning of the brain, and often seem to operate at a higher level of functional abstraction. The brain doesn’t have pain receptors on itself the way most of your body does; getting a migraine behind your left eye doesn’t actually mean that that specific lobe of your brain is what’s malfunctioning. It’s more like a general alert your brain is sending out that something is wrong, somewhere. And fibromyalgia often feels like it’s taking place in your entire body at once. Moreover, most neurological disorders are strongly correlated with mental disorders—indeed, the comorbidity of depression with migraine and fibromyalgia in particular is extremely high.

Which disorder causes the other? That’s a surprisingly difficult question. Intuitively we might expect the “more physical” disorder to be the primary cause, but that’s not always clear. Successful treatment for depression often improves symptoms of migraine and fibromyalgia as well (though the converse is also true). They seem to be mutually reinforcing one another, and it’s not at all clear which came first. I suppose if I had to venture a guess, I’d say the pain disorders probably have causal precedence over the mood disorders, but I don’t actually know that for a fact.

To stretch my analogy a little, it may be like a software problem that ends up causing a hardware problem, or a hardware problem that ends up causing a software problem. There actually have been a few examples of this, like games with graphics so demanding that they caused GPUs to overheat.

The human brain is a lot more complicated than a computer, and the distinction between software and hardware is fuzzier; we don’t actually have “code” that runs on a “processor”. We have synapses that continually fire on and off and rewire each other. The closest thing we have to code that gets processed in sequence would be our genome, and that is several orders of magnitude less complex than the structure of our brains. Aside from simply physically copying the entire brain down to every synapse, it’s not clear that you could ever “download” a mind, science fiction notwithstanding.

Indeed, anything that changes your mind necessarily also changes your brain; the effects of talking are generally subtler than the effects of a drug (and certainly subtler than the effects of an axe wound!), but they are nevertheless real, physical changes. (This is why it is so idiotic whenever the popular science press comes out with: “New study finds that X actually changes your brain!” where X might be anything from drinking coffee to reading romance novels. Of course it does! If it has an effect on your mind, it did so by having an effect on your brain. That’s the Basic Fact of Cognitive Science.) This is not so different from computers, however: Any change in software is also a physical change, in the form of some sequence of electrical charges that were moved from one place to another. Actual physical electrons are a few microns away from where they otherwise would have been because of what was typed into that code.

Of course I want to reduce the stigma surrounding mental illness. (For both selfish and altruistic reasons, really.) But blatantly false assertions don’t seem terribly productive toward that goal. Mental illness is different from physical illness; we can’t treat it the same.