Stress triggers old habits

A study by psychologists and researchers in Germany has uncovered the reason why people under stress are more likely to return to their old habits than to work towards a goal.

Cognition psychologists at the Ruhr-Universitaet-Bochum together with researchers from the University Hospital Bergmannsheil mimicked a stress situation in the body using drugs on 69 male and female volunteers. They then examined the volunteers' brain activity using MRI scanning.

In the study, reported in the Journal of Neuroscience, researchers discovered that hormones released by stress shut down brain activity in regions that deal with goal-directed behavior. However, the areas that governed habits were unaffected.

During the test, scientists used three hormones:a placebo, the stress hormone hydrocortisone and yohimbine, which helps keep another stress hormone, noradrenaline, active longer.

Volunteers where divided into four groups that received different substances:

• One got hydrocortisone alone.
• Another group got yohimbine.
• Others received both hydrocortisone and yohimbine.
• A fourthset of people were administered a placebo.

All participants were told they would get a chocolate pudding or orange juice as a reward if they chose certain symbols on a computer.Soon, the participants would learn that certain symbols were associated with getting pudding and others were linked to getting the juice.

After the first phase, the volunteers would get either as much chocolate pudding or as much juice as they wanted.

Theidea is that whoever gets a lot of either pudding or oranges will have less appetite for either and would stop choosing the symbols connected to the pudding or oranges in order not to get the food they had eaten so much of.

Researchers found that people who were given the stress hormones just kept choosing symbols that gave them more of the pudding or juice whereas those on placebo stopped that behaviour.

Examining the MRIs of the volunteers,researchers could see that the stress hormones reduced activity in the forebrainknown as orbitofrontal and medial prefrontal cortexwhich are associated with goal-oriented behaviour while the habit-driven part of the brain remained unaffected.