Stressed brains rely on habit

Exposure to chronic stress causes alterations in brain anatomy that may compel rats to rely too much on routine, even when a change in circumstances calls for a change in behavior, according to a new study published this week in Science. Image: Wikimedia commons, Janet StephensThe study provides "a really nice animal model for a subtle, important problem with cognition that can be caused by chronic stress in humans," neuroscientist linkurl:Robert Sapolsky;http://med.stanford.edu/profiles/Robert

By | July 30, 2009

Exposure to chronic stress causes alterations in brain anatomy that may compel rats to rely too much on routine, even when a change in circumstances calls for a change in behavior, according to a new study published this week in Science.
Image: Wikimedia commons, Janet Stephens
The study provides "a really nice animal model for a subtle, important problem with cognition that can be caused by chronic stress in humans," neuroscientist linkurl:Robert Sapolsky;http://med.stanford.edu/profiles/Robert_Sapolsky/ of Stanford University School of Medicine, who was not involved in the work, wrote in an email. "Plus some excellent neurobiology to go along with it." Habit formation is believed to be a way to conserve cognitive resources and make decisions more efficiently, as habits do not require constant evaluation of potential consequences. Driving home from work, for example, quickly becomes a matter of routine, leaving your mind free to daydream without missing a turn. However, some situations require alterations to such routines, such as stopping by the grocery store on the way home, in which case goal-directed attention is necessary for reaching your destination. In a series of behavioral experiments, neuroscientists linkurl:Rui Costa;http://www.fchampalimaud.org/care-research/cf-neuroscience-programme/research/rui-costa/ of the Champalimaud Foundation in Portugal and the National Institutes of Health (NIH) and colleagues determined that rats that had been stressed repeatedly and unpredictably for three weeks were more likely than unstressed animals to continue performing habitual behaviors, even when it no longer made sense to do so. "It's certainly a major finding," said neuroscientist linkurl:Henry Yin;http://fds.duke.edu/db/aas/pn/faculty/yinh of Duke University, who was not involved in the research. "This paper presents the very first evidence that stress can promote habitual behavior [in animals]." Chronic stress can also result in other behavioral symptoms, such as deficits in memory or spatial navigation. These changes are believed to be triggered by the release of corticosteroids, causing neuronal reorganization, primarily in the hippocampus and medial prefrontal cortex (mPFC). When the researchers measured the volume and density of various brains structures in stressed and unstressed rats, they found several differences. Most notably, the prelimbic cortex (PL) of the mPFC and the dorsomedial striatum (DMS) -- both implicated in goal-directed actions -- were reduced in size in stressed rats, while the dorsolateral striatum (DLS) -- necessary for habit formation -- was enlarged, suggesting a neurological mechanism for how stress affected their behavior. Previous work showed that habit formation involved the switch between neural circuits associated with goal-directed behavior and those controlling habitual behavior, Yin said, "[but] this is the first piece of evidence showing the structural basis for this kind of switch." "[It's] an important and novel contribution into the field," agreed neuroscientist linkurl:Patricia Janak;http://www.galloresearch.org/index.php/investigators/janaklab of the University of California, San Francisco, who was not involved in the work. "People typically had been thinking about chronic stress affecting circuits in the frontal cortex and circuits in the hippocampus. To look at the striatum, which controls a lot of our moment-by-moment behavior, is a really new direction." In the first set of tests, rats were trained to press a lever to receive a reward (either food pellets or sucrose). After two weeks of training, they were given full access to the reward and allowed to consume as much as they desired. When presented with the lever again, control animals stopped pressing the lever, but stressed animals didn't. If you get the dessert for free, Costa said, there's no need to work for it. "That's what control animals do," but stressed animals work anyway. In a second set of experiments, rats were trained to press one lever for pellets and the other for sucrose. Then, one of these two rewards was provided for free -- i.e., without a lever press. When the rats were given a choice of levers, control animals rightly pressed the lever that still required pressing to receive the reward, while stressed animals showed no preference between the two options. "It's not that they are stupid and don't understand that there is a difference," Costa said. "It's just that when given a choice, they will do the automatic thing." In fact, he said, these stress-induced changes seem almost adaptive. " When we are under chronic stress, it could be advantageous to use habitual strategies because [it reduces] the amount of cognitive resources that you need." Of course, when circumstances change, such a strategy can backfire. The findings, researchers say, provide a possible avenue for investigating therapies for stress-related disorders and addictive behavior. "We know stress is very often associated with compulsive drug use -- drugs tend to be used more often when you're stressed out," said Yin. "If we can figure out the molecular details underlying this, then maybe we'll be able to find some treatment for this."
**__Related stories:__***linkurl:The Science of Stress;http://www.the-scientist.com/article/display/55118/
[ November 2008]*linkurl:The Brain on Stress;http://www.the-scientist.com/article/display/53442/
[August 2007]*linkurl:Stress and alcohol;http://www.the-scientist.com/article/display/20371/
[3rd May 2002]
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Comments

Avatar of: anonymous poster

anonymous poster

Posts: 1

July 31, 2009

I think, it is very intresting paper and research. It would be good to study also stressed and un-stressed human behavior ( for example, stressed and unstressed postdocs). I suppose also, that the huge problem with obesity in USA is directly connected with stress-life. People eat more and more food, trying to eliminate stress and negative emotions, feelings. Based on this paper, it looks that to provide good life for people is equivalent to give them unstressful life.
Avatar of: anonymous poster

anonymous poster

Posts: 7

July 31, 2009

Regarding the previous post, are there really unstressed postdocs?
Avatar of: Christopher Lee

Christopher Lee

Posts: 50

July 31, 2009

Since the days when you could be hanged for a rabbit, poachers have known that if you frighten them they go into auto-pilot mode. They follow tracks as precisely defined as a long jumper's (or, for cricketers, bowler's) run-up. You place your nasty noose trap just before a landing spot.
Avatar of: RAVI NAMBY

RAVI NAMBY

Posts: 17

July 31, 2009

I AM GETTING THE SAME RESULT.\n\nINSTEAD OF MOUSE ONE CAN TAKE MY LIFE( MY BLOG- www.hisnobelwoes.blogspot.com) FOR STUDY.\n\nONE CAN EASILY UNDERSTAND MY BEHAVIOUR UNDER STRESS, BY READING MY BLOG.\n\nI USED TO GO ROUTINE, AND ALAWAYS UNDER VERY HIGH STRSS, READ MY BLOG www.hisnobelwoes.blogspot.com\n\nMY STRESSES ARE HIGHLY VISIBLE IN THE BLOG, AND LIKE MICE WHAT I AM DOING UNDER STRESS, DOING ROUTINE THINGS, AND NOT WASTING COGNITIVE ENERGY, FOR MUNDANE DAY TO DAY ACTIVITIES.\n\nWILL ANY REWARD TO ALLEIVATE FROM THE STRESS.\nNOT HAVING A CONTACT NUMBER( NO MOBILE OR LAND LINE)

August 4, 2009

Can someone please provide the link to the original article please?
Avatar of: Alison McCook

Alison McCook

Posts: 68

August 4, 2009

You can read the abstract of the original article here: http://www.sciencemag.org/cgi/content/abstract/325/5940/621\n\nAlison McCook\nDeputy Editor

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