Chronic stress can cause you to make risky decisions like picking a job with a good salary but strenuous hours, say scientists.
Researchers at Massachusetts Institute of Technology have identified the part of the brain that becomes impaired under stress and leads to poor decision-making.
The study showed that stress leads to a sort of mental confusion between choices that will or won’t be rewarding, and can last for months.
According to its authors, the study’s findings could lead to exciting prospects for treating anxiety and depression, and reducing the effects of stress to help people avoid bad – sometimes life-altering – decisions.
Scientists have linked chronic stress to a impairment of a particular part of the brain that can cause us to make high-risk decisions. But, according to the MIT researchers, they’ve also figured out how to manipulate that brain area to prevent these regrettable decisions
A lower-paid post with more leisure time appears less appealing when people are under mental pressure, according to new research.
Experiments on rats and mice found stressed out animals were far more likely to opt for dangerous alternatives, with a bigger reward.
They also identified impairments of a specific brain circuit underlying this abnormal decision making – and restored normal behavior by manipulating it.
It lies in the striatum, an area involved in planning and decision making which is also important for habit formation and linking action and reward.
The discovery could lead to treatments for patients with disorders such as depression, addiction, and anxiety which often feature poor decision making.
Senior author Professor Ann Graybiel, of Massachusetts Institute of Technology, said: ‘One exciting thing is by doing this very basic science, we found a microcircuit of neurons in the striatum we could manipulate to reverse the effects of stress on this type of decision making.
‘This to us is extremely promising, but we are aware that so far these experiments are in rats and mice.’
Making decisions in this type of situation, known as a ‘cost-benefit conflict’, is dramatically affected by chronic stress, she said.
The study, published in Cell, builds on research by the same team two years ago.
It found the circuit begins in the medial prefrontal cortex – responsible for mood control – and extends into clusters of neurons called striosomes, situated in the striatum.
They trained rodents to run a maze in which they had to choose between highly concentrated chocolate milk, which they like, along with bright light, which they don’t – or dimmer light but a weaker drink.
Blocking the connection between cortical neurons and striosomes, using light therapy called optogenetics, transformed their preference for lower risk, lower payoff choices to bigger payoffs despite their bigger costs.
In the latest study, the rodents were exposed to a short period of stress every day for two weeks.
Before experiencing stress, normal rats and mice would choose to run toward the maze arm with dimmer light and weaker chocolate milk about half the time.
The researchers gradually increased the concentration of chocolate milk found in the dimmer side, and as they did so, the animals began choosing that more frequently.
Somehow this prior exposure to chronic stress controls the integration of good and bad
Senior study author, professor Ann Graybiel of MIT
But when chronically stressed animals were put in the same situation, they continued to choose the bright light and better chocolate milk – even as the latter’s concentration greatly increased on the dimmer side.
This was the same behavior seen in rodents that had the prefrontal cortex-striosome circuit disrupted optogenetically.
Study co-author Dr Alexander Friedman said: ‘The result is the animal ignores the high cost and chooses the high reward.’
The researchers believe the circuit integrates information about the good and bad aspects of possible choices, helping the brain to produce a decision.
Normally, when the circuit is turned on, neurons of the prefrontal cortex activate brain cells called high firing interneurons, which then suppress striosome activity.
When the animals are stressed, these circuit dynamics shift and the cortical neurons fire too late to inhibit the striosomes, which then become overexcited. This results in abnormal decision making.
Prof Graybiel said: ‘Somehow this prior exposure to chronic stress controls the integration of good and bad.
‘It is as though the animals had lost their ability to balance excitation and inhibition in order to settle on reasonable behaviour.’
Once this shift occurs, it remains in effect for months.
But the researchers were able to restore normal decision making in the stressed mice by using optogenetics to stimulate the high-firing interneurons, thereby suppressing the striosomes.
This suggests the prefronto-striosome circuit remains intact following chronic stress and could potentially be susceptible to manipulations that would restore normal behavior in human patients whose disorders lead to abnormal decision making.
Dr Friedman added: ‘This state change could be reversible, and it is possible in the future that you could target these interneurons and restore the excitation-inhibition balance.’