According to a new study in Science, rats who are chronically stressed not only become poor decision−makers and engage in almost obsessive−compulsive behaviors, but these behavioral changes exist as an unfortunate result of rewiring in their brains. Luckily, these changes — behavioral and physical — reverse themselves when the rats are allowed to de−stress.
Luckily, after four weeks of a stress−free existence, the formerly frazzled rats behaved just like controls — their brains had also returned to the normal, unstressed state.
Researchers led by Muno Sousa at the University of Minho in Portugal stressed rats in one of a few different ways: exposing them to electric shocks, putting them in a cage with dominant rats, or dipping them in water for a period of time. After four weeks of these nerve−wracking events, the rats were fairly stressed.
To determine how the stressed out animals — and their brains — had changed in comparison to unstressed rats, the researchers carried out a couple of different tests. In one, hungry rats learned that they could press a bar for food or sugar−water (both groups, stressed and unstressed rats, learned this part just fine). The researchers then made sure the animals were well−fed before letting them at the levers. As one might suspect, the unstressed animals pressed the levers significantly less (because they were full), but the stressed rats continued to press it just as often as they had before, a lesson perhaps for people who eat when stressed.
Normally rats are fairly clever creatures, but, as the researchers point out, the stressed rats stopped paying attention to changes in the environment — they were acting out of rote behavior, as if mentally stuck in a rut. It is possible that stressed people are similarly blind to new situations.
The team found that there were noticeable brain changes to go along with these behavioral differences. In one area, the dorsomedial striatum, which controls goal−directed behaviors (like learning to press a lever to receive a douse of sugar water), the connections between cells had dwindled so that neurons were not communicating with one another as they should. Another region, the dorsolateral striatum, which controls habit−like behaviors (such as continuing to press the food lever even though you’re full), had expanded and formed more connections between cells.
These findings suggest chronic stress makes rats – and possibly humans — more prone to falling back on habit, rather than responding appropriately to changes in the world around them. Sousa says that “[b]ehaviors 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. I call this a vicious circle.”
Luckily, after four weeks of a stress−free existence, the formerly frazzled rats behaved just like controls – their brains had also returned to the normal, unstressed state.