Natalie Angier has an excellent column on the self-defeating feedback loop triggered by chronic stress. According to a new paper, when mice are chronically stressed, they end up reverting to habit and routine, even though these same habits are what led to the chronic stress in the first place:
Reporting earlier this summer in the journal Science, Nuno Sousa of the Life and Health Sciences Research Institute at the University of Minho in Portugal and his colleagues described experiments in which chronically stressed rats lost their elastic rat cunning and instead fell back on familiar routines and rote responses, like compulsively pressing a bar for food pellets they had no intention of eating.Moreover, the rats' behavioral perturbations were reflected by a pair of complementary changes in their underlying neural circuitry. On the one hand, regions of the brain associated with executive decision-making and goal-directed behaviors had shriveled, while, conversely, brain sectors linked to habit formation had bloomed.
In other words, the rodents were now cognitively predisposed to keep doing the same things over and over, to run laps in the same dead-ended rat race rather than seek a pipeline to greener sewers. "Behaviors become habitual faster in stressed animals than in the controls, and worse, the stressed animals can't shift back to goal-directed behaviors when that would be the better approach," Dr. Sousa said. "I call this a vicious circle."
As I noted in this article, I think there's increasing evidence that chronic stress plays a pivotal role in a wide variety of mental disorders, including depression. Stress works its ravages in large part by suppressing the release of trophic factors. in the brain. (Trophe is Greek for nourishment; what sunlight and water do for trees, trophic factors do for brain cells.) In a series of influential papers published earlier this decade, Ronald Duman at Yale demonstrated that the same destructive hallmark is seen in depression, so that our neurons are deprived of what they need. (From the perspective of evolution, this response makes sense: in chronically stressful conditions, it probably doesn't make sense to invest in a lavish cortex.)
Obviously, there's a huge gap between less robust brain cells and habit-loving mice, but I think the theme connects: chronic stress reduces cellular plasticity (including neurogenesis), which might make us (and mice) more likely to settle into familiar ruts and routines. The end result is that people stick with the very behaviors that created the stress in the first place.
This penchant for self-destructive routines also plays out at the level of everyday thought. I think there's some intriguing evidence showing how being depression can make it that much harder to escape the mood disorder, as one gets stuck in a whirlpool of negativity. Consider some elegant work done by John Jonides and colleagues on an experimental exercise known as the "suppression task". Subjects are given four random words, two of which are printed in blue and two in green. After reading the words, they're told to forget all the blue words and remember all the green words. Then, the scientists provide a steady stream of "probe words" and ask the subjects whether or not each probe is one of the words they were asked to remember. Interestingly, Jonides has found differences between clinically depressed and control subjects on the suppression task. While people suffering from depression perform normally when trying to forget words with a positive association ("smile," "sunny," etc.), they're much worse at forgetting words with a negative association, such as "hurtful" or "lonely". This suggests that being depressed primes us to fixate on problems, on all the things that are wrong with us and the world. The end result is a recursive loop of miserable thoughts, which leads to more stress, and more misery.
The larger point of this research, of course, is that it's imperative to seek medical help for serious cases of depression. It's hard to escape a downward spiral by yourself.
Brain & Behavior
Comments (20)
The best part of that study is definitely that fact that a 4 week vacation from stress helped the rats get back to normal.
Posted by: becca | August 18, 2009 12:40 PM