Pack Up: Rats Say You Need a Break

Image by gingerpig2000 via Flickr

It’s August, which means a lot of you aren’t reading blogs. You’re on vacation. Bad for blog traffic (which comes when you’re slacking off at work) — though Neuroworld is actually having a pretty good traffic month, thanks guys! — good for your brain.

Stress screws you up big time — it puts you in a stress loop. Vacation breaks the loop.

Just ask rats:

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.”

Aside from the fact that Elastic Rat Cunning would make a great name for a band, the take away here is that stress isn’t just unpleasant — it’s self-perpetuating. You engage in a routing that makes you stressed, you become stressed, you fall back further on that routine, it makes you more stressed, etc.

And, as Jonah Lehrer points out, these sort of loops aren’t limited to stress — they’re also a key player in depression:

[T]here’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 good news?

A vacation can break the cycle (at least for stress):

Happily, the stress-induced changes in behavior and brain appear to be reversible. To rattle the rats to the point where their stress response remained demonstrably hyperactive, the researchers exposed the animals to four weeks of varying stressors: moderate electric shocks, being encaged with dominant rats, prolonged dunks in water. Those chronically stressed animals were then compared with nonstressed peers. The stressed rats had no trouble learning a task like pressing a bar to get a food pellet or a squirt of sugar water, but they had difficulty deciding when to stop pressing the bar, as normal rats easily did.

But with only four weeks’ vacation in a supportive setting free of bullies and Tasers, the formerly stressed rats looked just like the controls, able to innovate, discriminate and lay off the bar. Atrophied synaptic connections in the decisive regions of the prefrontal cortex resprouted, while the overgrown dendritic vines of the habit-prone sensorimotor striatum retreated.

According to Bruce S. McEwen, head of the neuroendocrinology laboratory at Rockefeller University, the new findings offer a particularly elegant demonstration of a principle that researchers have just begun to grasp. “The brain is a very resilient and plastic organ,” he said. “Dendrites and synapses retract and reform, and reversible remodeling can occur throughout life.”

If a rat’s brain resets itself in four weeks, what’s the number for humans? Hopefully less than that, since — in America, at least — most humans don’t get four weeks. This ain’t France.

Stress has its uses (otherwise, we and other animals wouldn’t feel it). It puts us on automatic so that we can dedicate more mental resources to responding to whatever’s “threatening” us. But we also need to take active steps to combat it, when it has us in its grasp. August is as good a month as any for that. Hope you’re enjoying.