Thinking and depression

One of the latest efforts to make sense of depression is in this week's New York Times Magazine - Depression’s Upside.
The article profiles research by Andy Thomson and Paul Andrews on the vexing question - why does depression exist? Given that the illness/condition affects such a large percentage of the population (about seven percent of the population in a year and, apparently, across cultures), why is this response so common and what is the irritant that's causing it?
Their research shows that depressed patients commonly have a hyperactive left ventrolateral prefrontal cortex (VLPFC). Activity in the VLPFC is also associated with a particular type of deeply analytical thinking.
The depressed mood, then, is not so much a response to thinking sad thoughts, but our response to extended periods of that type of analytical thinking. The article notes, "this deliberate thought process is slow, tiresome and prone to distraction; the prefrontal cortex soon grows exhausted and gives out."
There are plenty of critics of this view, that people with depression are in a deep state of rumination. This is, in part, due to the problems we have in defining and diagnosing depression. The illness/condition is an amalgamation of symptoms present over time (typically two or more weeks). Doctors build a circumstantial case for the diagnosis. They're sometimes able to identify a cause (family crisis, work troubles, long-standing relationship issues) and sometimes they can't identify a triggering event.
"To say that depression can be useful doesn’t mean it’s always going to be useful,” Thomson says. “Sometimes, the symptoms can spiral out of control."
Thomson goes on to ask, "Do these ideas help me treat my patients better?" Based on this research, he's less inclined to prescribe antidepressants, instead setting up frameworks to help patients discover what's triggering this ruminative response.
The idea that many people with depression will respond better to cognitive therapy and less to antidepressants is borne out in other research. A meta-analysis of research into the effectiveness of antidepressants, published in the Journal of the American Medical Association,  (Antidepressant Drug Effects and Depression Severity) showed that effectiveness of antidepressants increased with the severity of depression. Antidepressants for patients with mild-to-moderate depression weren't much better than treatments with placebo. For patients with severe depression, antidepressants were beneficial.
What we're finding, then, is that the easiest, cheapest, and least-effective ways of treating mild-to-moderate depression are found in the prescription of antidepressants.
As we're often reminded - fast, cheap, good: pick two.