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Let’s revisit the question I posed in my “Quitters Are Winners Too” post: what is it about American life that increases the prevalence of depression? Americans are more depressed than any other group in the world. The answer offered by evolutionary medicine is that the persistence required to fulfill grandiose goals undermines our natural response (low mood) which acts as a warning sign that protects us from severe depression by prompting us to withdraw from unrealistic or unattainable goals. Because American culture, more than any other, promotes the pursuit of grandiose goals, Americans are more likely to suffer from major depression.

It’s an interesting theory, but I have another explanation. While I have no scientific expertise in the field of evolutionary medicine, nevertheless, personal experience gives me some credibility. As a person who has struggled for years with episodes of major depression etc. etc., I speak from within. This doesn’t constitute “evidence,” but it might suggest directions for further research, especially given that my observations are entirely compatible with the perspective of evolutionary medicine. Also, my thoughts shouldn’t be taken as a rejection of the “American grandiosity” theory. Multiple explanations for major depression are probable.

Here’s my take on things: major depression is a reaction to suppression of our natural capacity to filter stimuli.

What the heck does that mean?

Let me unpack this statement by working backwards.

Filter Stimuli – Think for example of a funnel, wide at the top and narrow at the bottom. We use a funnel to take a large flow of liquid and reduce it to a narrower flow. Let’s say, for example, that we want to pour water from a pail into a narrow-necked bottle. A funnel reduces the greater flow from the pail so that the bottle can “cope.”

Something analogous happens with our sensory perceptions. When we look at the world, our vision is restricted to a narrow band of electromagnetic radiation (the visible spectrum). Imagine what things would look like if we could also see infrared, ultraviolet, x-ray and gamma radiation. Imagine how much more information our brains would have to process. The same is true of hearing. See my earlier post on presbycusis and the natural limitation in the range of frequencies we can hear.

These are examples of physiological filtering. The body has adapted to restrict the kind and amount of information the brain receives. However, there is also cognitive filtering – tricks the brain plays to further reduce the amount of information it has to cope with. For example, we intuitively downplay the significance of objects at rest and respond more readily to those that move. We filter out ambient noise. We focus attention on one thin to the exclusion of others. These are all cognitive strategies which, like the funnel, work to help us cope. These are habits we have evolved and they are natural.

Suppression – Short of self-mutilation, there is little we can do to suppress our physiological capacity for filtering data. We see what we see. We hear what we hear. But there are lots of ways we can suppress our cognitive capacity. Artificial stimulants like coffee and cocaine, for example, can make us more susceptible to stimuli. Sounds are louder. Things are brighter. We’re more awake to everything around us. But there are natural ways we engage in suppression of our filtering capacity. The most obvious of these is fatigue. As we grow tired, it becomes more difficult to cope with stimuli. The consequences – irritability, impatience anxiety, anger – appear in scenarios that are familiar to us all:

• the harried parent with the screaming kids;
• the student who’s pulled an all-nighter before an exam;
• the night-shift worker who drives home in a blazing dawn sky to a house full of kids getting ready for school.

In all these scenarios, it’s normal to seek a temporary retreat. The parent may try to pass off the children to the other parent or to a baby-sitter for some “me-time.” Or if the parent lacks those supports, there’s always mother’s little helper. Following a thousand-year tradition begun in the great universities of Europe, the student will cap a final exam with a trip to the local pub. And a night-shift worker will simply draw the blinds and go to bed.

Fatigue has a natural conclusion – sleep. Migraine headaches function in the same way. They are a response to overwhelm of one sort or another and force the sufferer to shut down.

Depression – Clinical depression is an exaggerated response to overwhelm. It is like sleep or the total withdrawal that migraine requires. It provides a defense against excessive stimuli (including emotional stimuli). Symptoms like hypersomnia and anhedonia (and the related issue of anxiety, esp. phobia and social anxiety disorder) are strategies to avoid stimuli. The “learned helplessness” theory of depression can also be drawn into this explanatory framework: the depressive’s expression of helplessness is like the parent who seeks relief from crying children by hiring a baby-sitter. It’s a way to signal the need for relief from overwhelm. It is also entirely consistent that depressives self-medicate with CNS depressants like alcohol and benzodiazepines like Valium and Rivotril. And the fatal outcome of depression, suicide, is the ultimate withdrawal. (Though suicide can have many other motivations as well.)

If I am right (admittedly a big “if”), then it isn’t surprising that a culture which nurtures/celebrates/markets stimulus would have a higher prevalence of major depression. American culture burdens our innate capacity to filter stimulus. It is noisy, aggressive, and unrelenting. It is the always-open commerce of New York City. It is the billboards that line the Interstate highways. It is the glitz and flash of Las Vegas. It is a thousand channels, satellite radio, a billion dot-com domains, and hundreds of “friends” keeping us up-to-date through social networking rss feeds. For those of us with only a modest capacity to filter this onslaught of information, it is understandable that we should need to shut down from time to time. Some do it with planned withdrawals like retreats and holidays. Some do it with substances. Some, like me, fall into episodes of major depression and – at least for a time – drop off the face of the planet.

Related posts:

1. Fluff American Style – The Social Network