Thursday, July 30, 2009
Flustered Rats Stuck in a Rut
By Michael Torrice
ScienceNOW Daily News
30 July 2009
Scientists at the University of Minho in Portugal and the U.S. National Institutes of Health (NIH) in Bethesda, Maryland, compared stressed and unstressed rats' responses to two tests. In the first test, they taught the rats to hit a lever to score one of two possible treats: a sip of a sugary solution or a food pellet. The scientists then changed the game, providing the rats with all of the snacks they wanted before giving them the option to press the lever. Satiated, the unstressed rats hit the lever significantly less. But the stressed rats continued pressing at the same rate.
For the second test, the scientists trained the rodents to use two levers, one for each treat. After the rats learned the rules, the researchers picked one treat to dispense randomly, whether or not the rat hit the lever. The relaxed animals hit that treat's lever less often, while the stressed rats continued to hit both levers with equal frequency.
In both experiments, the stressed rats acted out of habit and didn't respond to the changes around them--they were stuck in a rut....The researchers conclude in tomorrow's issue of Science that chronic stress rewires brain areas involved in the switch between goal-directed and habitual actions. Rui Costa, an NIH neuroscientist and co-author of the study, says that "those changes in the brain bias your behavior tremendously for a while after the stress."....The study provides an animal equivalent to "a frequent, maladaptive feature of human behavior during stress: We fall into doing the same thing ... instead of trying something new,"