For many people, stress is the factor that unravels diets, exercise plans and other goal-directed tasks.
European researchers believe they have discovered why stressed persons are more likely to lapse back into old habits rather than follow a goal-directed agenda.
In a study, investigators determined stress hormones shut down the activity of brain regions for goal-directed behavior, yet do not affect the brain regions responsible for habitual behavior.
Researchers from the Ruhr-Universität in Germany, together with colleagues from the University Hospital Bergmannsheil, mimicked a stress situation in the body using drugs. They then examined the brain activity using functional MRI scanning.
The scientists found that the interaction of the stress hormones hydrocortisone and noradrenaline shut down the activity of brain regions for goal-directed behavior. Yet the brain regions responsible for habitual behavior remained unaffected.
During the research on different stress hormones, the cognitive psychologists used three substances: a placebo, the stress hormone hydrocortisone and yohimbine. Yohimbine is a product which ensures that the stress hormone noradrenaline stays active longer.
Some study participants received hydrocortisone alone or just yohimbine, while other participants received both substances. A fourth group was administered a placebo. Altogether, 69 volunteers participated in the study.
During the experiment, all participants, both male and female, learned that they would receive cocoa or orange juice as a reward if they chose certain symbols on the computer.
After this learning phase, volunteers were allowed to eat as many oranges or as much chocolate pudding as they liked. “This procedure weakens the value of the reward,” said Lars Schwabe, Ph.D.
“Whoever eats chocolate pudding will lose the attraction to cocoa. Whoever is satiated with oranges, has less appetite for orange juice.”
In this context, goal-directed behavior means: Whoever has previously eaten the chocolate pudding chooses the symbols leading to cocoa reward less frequently. Whoever is satiated with oranges selects less frequently the symbols associated with orange juice.
The findings show that only the combination of yohimbine and hydrocortisone attenuates or satisfies goal-directed behavior.
As expected, volunteers who took yohimbine and hydrocortisone did not behave in a goal-directed manner but according to habit. In other words, satiation with oranges or chocolate pudding had no effect.
Persons who had taken a placebo or only one medication, on the other hand, behaved goal-directed and showed a satiating effect.
The brain data revealed: The combination of yohimbine and hydrocortisone reduced the activity in the forebrain – in the so-called orbitofrontal and medial prefrontal cortex.
Researchers say that these areas have been previously associated with goal-directed behavior. The brain regions which are important for habitual learning, on the other hand, were similarly active for all volunteers.
Source: Ruhr-University Bochum