+ Chronic Stress-Loops in Brain Change Behavior

other topics: click a “category” or use search box

In an article in the NY Times, Natalie Angier writes that chronic stress changes the brain, but relaxation can change it back.

In the journal Science this summer, Nuno Sousa of the Life and Health Sciences Research Institute in Portugal says he and his colleagues found that rats, if chronically stressed, lost their elastic rat cunning — they instead fell back on familiar routines and rote responses.  They would, for example, compulsively press a bar for food pellets they had no intention of eating.

Brain Changes

In addition, the rats’ behavioral oddnesses 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.  Conversely, brain sectors linked to habit formation had bloomed.

In other words, rats were now cognitively disposed to keep doing the same things over and over, to “run laps in the same dead-end rat race rather than seek a pipeline to greener sewers,” writes Angier.  And Dr Sousa says,

“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.”

A neurobiologist who studies stress at Stanford, Robert Sapolsky, says

“This is a great model for understanding why we end up in a rut, and then dig ourselves deeper and deeper into that rut.”

In fact, continues Sapolsky, humans are lousy at recognizing when their normal coping mechanisms aren’t working.  We usually try it five more times, when it would have been better to try something new.

While perseverance is an admirable trait — is indeed essential for success in life — if it’s taken too far it becomes “perseveration.”  Perseveration is  uncontrollable repetition.  Taken to extremes, it simply seems perverse.

Dr Sapolsky is the author of “Why Zebras Don’t Get Ulcers.” 

“If  I were to try to break into the world of modern dance, after the first few rejections the logical response might be, practice even more.  But after the 12,000th rejection, maybe I should realize this isn’t a viable career option.”

But It Can Be Reversed

Luckily, it appears that stress-induced changes in behavior and brain can be reversed.  

After four weeks’ vacation in a supportive setting free of bullies, Tasers and dunking in water, the formerly stressed rats looked just like the controls.  They were able to innovate, discriminate and refrain from obsessive behavior.

Atrophied synaptic connections in the decisive regions of the prefrontal cortex resprouted, while the overgrown dendritic vines of the habit-prone sensorimotor striatum retreated.

Says Bruce McEwen, head of the neuroendocrinology lab 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.  Dendrites and synapses retract and reform, and reversible remondeling can occur throughout life.”

We associate stress with the split-second pace of our wired society.  But the body’s stress response is one of our oldest attributes.  Its basic architecture, with its linked network of neural and endocrine organs that spit out stimulatory and inhibitory hormones and other factors as needed, looks pretty much the same in a human as it does in a goldfish or a red-spotted newt.

Our stress response is itself dynamic.  It was essential for maneuvering through a dynamic world.  We had to dodge predators and chase down prey; we swung through trees; we fought off disease. 

As we go about our days, says McEwen, the biochemical mediators of the stress response rise and fall, flutter and flare.  “Cortisol and adrenaline go up and down.  Our inflammatory cytokines go up and down.”

The target organs of stress hormones likewise “dance to the beat ,” writes Angier.  The heart races and slows, the intestines constrict and relax.  This system of so-called allostasis, of maintaining control through constant change, stands in contrast to the mechanisms of homeostasis that keep the pH level and oxygen concentration in the blood within a narrow and invariant range.

But the dynamism of a person’s stress response makes it vulnerable to disruption, especially when the system is treated too roughly and not according to instructions.

In most animals, a serious threat provokes activation of the stimulatory, sympathetic, “fight or flight” side of the stress response.  But when the danger has passed, the calming parasympathetic circuitry tamps everything back down to baseline flickering.

Humans, however, have a brain that can think too much, that can extract phantom threats on a daily and sometimes hourly basis.  Over time such constant hyperactivation of the stress response can unbalance the entire feedback loop.

Reactions which would be desirable in limited, targeted quantities become hazardous in “promiscuous excess,”  writes Angier.  You need a spike in blood pressure if you’re going to run, to speedily deliver oxygen to your muscles.  But chronically elevated blood pressure is a source of mutiple medical miseries.

We might ask, why should the stressed brain be prone to habit formation? 

Perhaps — to help shunt as many behaviors as possible over to automatic pilot, so we can focus on the crisis at hand.

sole source: NY Times article by Natalie Angier on 8/18/09.  www.nytimes.com   

tutoring in columbus OH:   Adrienne Edwards   614-579-6021   or email  aedwards tutor@columbus.rr.com

Advertisements

Comments are closed.