First of all, thank you to everyone who took the time to write and comment on my recent article on depression. I really appreciated all the insightful emails and I’m trying to respond to every one. In the meantime, I wanted to address some important criticisms of the analytic-rumination hypothesis and of my article, which were raised by an academic psychiatrist. I’ve reproduced his criticisms, and my replies, below:
First, you write “depression is everywhere, as inescapable as the common cold”. No, this is flatly wrong. Major depression is estimated by an absurdly broad range of epidemiological studies to have a slightly less than 20% lifetime prevalence.
I talked to more than a dozen mental health professionals about this precise issue. The general consensus, as near as I could tell, was that the 20 percent range is actually at the low end of the current estimates for lifetime prevalence for MDD. One of the problems with estimating “lifetime prevalence” is that most surveys are based on retrospective memories, as people try to reconstruct their state of mind decades earlier. There’s good evidence that such surveys reliably underestimate the number of people who suffer from major depressive disorder. Consider this recent study, which conducted interviews with a random sample of Canadians during a relatively brief time span. Here are their conclusions:
The annual prevalence of MDD ranged between 4% and 5% of the population during each assessment, consistent with existing literature. However, 19.7% of the population had at least one major depressive episode during follow-up. This included 24.2% of women and 14.2% of men. These estimates are nearly twice as high as the lifetime prevalence of major depressive episodes reported by cross-sectional studies during same time interval. CONCLUSION: In this study, prospectively observed cumulative prevalence over a relatively brief interval of time exceeded lifetime prevalence estimates by a considerable extent. This supports the idea that lifetime prevalence estimates are vulnerable to recall bias and that existing estimates are too low for this reason.
And this is merely the latest longitudinal study to estimate a significantly higher percentage of people suffering from major depressive disorder. One longitudinal study of adolescents living in New Zealand showed that 37% satisfied either the third edition-revised of the DSM or the DSM-IV-TR for a diagnosis of a lifetime episode of major depression.
Obviously, it will always be difficult to precisely estimate the percentage of people suffering from a condition over a long period of time. For one thing, the diagnosis of major depressive disorder is itself in flux. However, I think there are good reasons to believe that the standard estimate of 20 percent is at the low end of the spectrum, especially given current trends. Since 1980, the diagnosis of depression has been rapidly increasing across every segment of the population. To take but one example: between 1992 and 1998 there was a 107 percent increase in depression among the elderly.
Here’s another criticism:
Next – and this is most surprising to me – you rehash their arguments about the VLPFC as though it exists as a kind of anatomic source of depression. Surely you are aware – in fact I know you are because you have written at other times about this very topic – about just how complicated our current evidence base is in the area of depression. I mean even just to mention the well known deficits in hippocampal neurogenesis, the excess activity of the amygdala, or any number of other known reciprocal interactions between subcortical and prefrontal cortices would help an educated lay reader understand that while the VLPFC may be particularly active in ruminative processes, it still needs to be understood in the context of broader functional neuroanatomic findings in depression.
I’m sympathetic to this criticism. In an ideal world, I would have spent another thousand words or so outlining the neuroscience of depression; there is always more to say about a subject as rich and complex as mental illness. As noted above, there are many changes visible in the brains of people suffering from major depressive disorder. (I’ve written at length in other publications about many of these changes, particularly the reduction of neurogenesis.) It’s also worth pointing out that many of these changes don’t appear to be unique to major depressive disorder, but are rather part of larger response to chronic stress. As we now know, chronic stress is toxic for the brain, and tends to shrink the hippocampus and swell the amygdala. (Of course, like just about result in neuro-psychiatry, this claim remains controversial.) Alas, this was not an article about the neuroscience of depression, and so I was only able to discuss the proposed neural substrate of rumination in the VLPFC as it pertained to the analytic-rumination hypothesis. I never claim, of course, that the VLPC is the neural signature for MDD.
I’ve also received several emails from psychiatrists who criticize my reference to the DSM. Here’s a sample email:
I’ve begun e-mailing every author I encounter who uses a phrase like “diagnostic bible” to describe the DSM to ask them to please think a little further on the subject. If there is any use for the DSM at all in the real world, it arises from the intention to create a heuristic document. That is, the very purpose of DSM is to closely describe our current understanding of diagnostic entities so that they may be tested against reality. The purpose is not to hand down scripture from psychiatric gods to psychiatric priests; the purpose is to provide a little handbook that a large group of explorers can use to map out a territory. In psychiatry, we are still trying to figure out whether this or that psychiatric diagnosis accurately describes anything in the real world, or whether it is simply a projection of the the mind of an individual or a culture. DSM, at its best, recognizes that we are largely still groping in the dark, trying to discern what is illness and what is health, whether treatment is needed or can be accomplished.
I think this is right, and I regret my use of the phrase “bible of psychiatry”. I had no intention of suggesting that the DSM is a document of faith, only that it’s an authoritative resource for modern psychiatry. But it was a thoughtless, cliched description.
Needless to say, there are many more criticisms to make, both of the ideas described in the article and of the article itself. As you can imagine, this is a difficult subject to write about, in large part because the facts themselves are so contested. As demonstrated in this widely cited survey, patients with major depressive disorder exist on a continuum of severity, from mild to severe, making it ridiculous to suggest that there is, or should be, only one form of treatment. If a treatment works for the individual patient that is the only fact that matters. Everything else is mere theory.