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Stress tweaks brain to sabotage self control

Weakened willpower When life gets stressful, it is only natural that you should reach for the chocolate bar rather than an apple.

At least that is the finding of a Swiss study that shows how stress alters the brain's network to impair self-control.

The finding, published today in the journal Neuron, helps explain why people under stress choose short-term gain over long-term goals.

For the study the researchers at the University of Zurich, recruited 51 participants who reported they were making an effort to maintain a healthy lifestyle, but still enjoyed and consumed junk food.

Twenty-nine of the cohort were subjected to moderate stress by having their hand submerged in ice water for three minutes while being filmed and observed.

All participants were then asked to choose between eating a very tasty but unhealthy food item, or a healthy but relatively less tasty item.

First author Silvia Maier, from the Laboratory for Social and Neural Systems Research in the Department of Economics, says those who had been subjected to stress were more likely to select an unhealthy food.

This was despite being reminded which foods were better for them during the experiment.

Maier says the brain's decision to risk long-term gain for a short-term benefit is best understood from an evolutionary perspective.

"One widespread idea about the stress response is that it prepares the body for 'fight or flight'," she says.

"So that means it is helping to take an appropriate action right now. If you look at self-control problems from this angle, it might seem more important and prioritised under stress to cope with the stressor and the stress reaction.

"Long-term goals would have to take a backseat in this situation and would have to wait until the stressful situation has been resolved."

Brain connections

As part of the study the researchers used functional magnetic resonance imaging of the stressed participants to track changes in neural activity.

Maier says key to the brain's decision-making is the ventromedial prefrontal cortex (vmPFC), which helps the brain to calculate values for different choice options.

"For example, in order to choose between different foods, our brain needs to integrate all characteristics of each option that are important for our choice, (for example, how healthy and tasty each food option is) and compare these overall values," Maier says.

"Whatever we think is the option with the highest overall value (so combining all these characteristics) is what we choose in the end."

To know what matters most in the moment when we make the choice, the vmPFC exchanges information with other areas in the brain that care about different aspects of choice options, she says.

Maier says while much of this was already known through previous studies their work revealed an interesting twist -- after stress there is increased communication between reward regions of the brain -- the striatum and amygdala -- and the vmPFC.

At the same time, as the level of stress a person experiences increases, regions of the dorsolateral prefrontal cortex that are involved in goal maintenance and long-term planning, communicate less effectively with vmPFC.

"You could say it's almost like stress is turning up the dial on signals about taste, and turning down the signal on health," she says.

However Maier points out the stressed participants still care about eating healthily, they just cannot resist at that moment if presented with a strong temptation, like their favourite chocolate bar.

"Going forward, we need to understand better how the details of these effects have an impact on the brain and how we might be able to modify them," Maier says.

"Our findings show that self-control is mediated by a complex and distributed network in the brain. That means that self-control could be impaired by disturbances in any number of regions within this network.

"But on the other hand, that also means that there might be multiple ways of enhancing self-control or preventing self-control problems. Those are exciting possibilities for future research."

Related: Can you boost your willpower?