Everyone knows that chronic stress is dangerous, especially for the developing brain. It prunes dendrites and inhibits the birth of new neurons. It shrinks the hippocampus, swells the amygdala and can lead to an elevated risk for heart disease, depression and diabetes. At times, these persuasive studies can make it can seem as if the ideal childhood is an extended vacation, shielded from the struggles of life.
But the human brain resists such simple prescriptions. It is a machine of tradeoffs, a fleshy computer designed to adapt to its surroundings. This opens the possibility that childhood stress - even of the chronic sort - might actually prove useful, altering the mind in valuable ways. Stress is a curse. Except when it's a benefit.
A new paper by a team of scientists at the University of Minnesota (Chiraag Mittal, Vladas Griskevicius, Jeffry Simpson, Sooyeon Sung and Ethan Young) investigates this surprising hypothesis. The researchers focused on two distinct aspects of cognition: inhibition and shifting.
Inhibition involves the exertion of mental control, as the mind overrides its own urges and interruptions. When you stay on task, or resist the marshmallow, or talk yourself out of a tantrum, you are relying on your inhibitory talents. Shifting, meanwhile, involves switching between different trains of thought. “People who are good at shifting are better at allowing their responses to be guided by the current situation rather than by an internal goal,” write the scientists. These people notice what’s happening around them and are able to adjust their mind accordingly. Several studies have found a correlation between such cognitive flexibility and academic achievement.
The researchers focused on these two cognitive functions because they seemed particularly relevant in stressful childhoods. Let’s start with inhibition. If you grow up in an impoverished environment, you probably learn the advantages of not waiting, as delaying a reward often means the reward will disappear. In such contexts, write the scientists, “a preference for immediate over delayed rewards…is actually more adaptive.” Self-control is for suckers.
However, the opposite logic might apply to shifting. If an environment is always changing – if it’s full of unpredictable people and intermittent comforts – then a child might become more sensitive to new patterns. They could learn how to cope by increasing their mental flexibility.
It’s a nice theory, but is it true? To test the idea, the Minnesota scientists conducted a series of experiments and replications. The first study featured 103 subjects, randomly divided into two groups. The first group was given a news article about the recent recession and the lingering economic malaise. The second group was given an article about a person looking for his lost keys. The purpose of this brief intervention was to induce a state of uncertainty, at least among those reading about the economy.
Then, all of the subjects were given standard tasks designed to measure their inhibition and shifting skills. The inhibition test asked subjects to ignore an attention-grabbing flash and look instead at the opposite side of the screen, where an arrow was displayed for 150 milliseconds. Their score was based on how accurately they were able to say which way the arrow was pointing. Switching, meanwhile, was assessed based on how quickly subjects were able to identify colors or shapes after switching between the categories.
Once these basic cognitive tests were over, the scientists asked everyone a few questions about the unpredictability of their childhood. Did their house often feel chaotic? Did people move in and out on a seemingly random basis? Did they have a hard time knowing what their parents or other people were going to say or do from day-to-day?
The results confirmed the speculation. If people were primed to feel uncertain – they read that news article about the middling economy – those who reported more unpredictable childhoods were significantly worse at inhibition but much better at shifting. “To our knowledge, these experiments are the first to document that stressful childhood environments do not universally impair mental functioning, but may actually enhance certain cognitive functions in the face of uncertainty,” write the scientists. “These findings, therefore, suggest that the cognitive functioning of adults reared in more unpredictable environments may be better conceptualized as adapted rather than impaired.”
After replicating these results, the scientists turned to a sample of subjects from the Minnesota Longitudinal Study of Risk and Adaptation. (I’ve written about this incredible project before.) Begun in the mid-1970s, the Minnesota study has been following the children born to 267 women living in poverty in the Minneapolis area for nearly four decades. As a result, the scientists had detailed data on their childhoods, and were able to independently assess them for levels of stress and unpredictability.
The scientists gave these middle-aged subjects the same shifting task. Once again, those adults with the most chaotic childhoods performed better on the test, at least after being made to feel uncertain. This suggests that those young children forced to deal with erratic environments – they don’t know where they might be living next month, or who they might be living with – tend to develop compensatory skills in response; the stress is turned into a kind of nimbleness. This difference is significant, as confirmed by a meta-analysis:
Of course, this doesn’t mean poverty is a blessing, or that we should wish a chaotic childhood upon our children. “We are not in any way suggesting or implying that stressful childhoods are positive or good for people,” write Mittal, et al. However, by paying attention to the adaptations of the mind, we might learn to help people take advantage of their talents, even if they stem from disadvantage. If nothing else, this research is a reminder that Nietzsche had a point: what doesn’t kill us can make us stronger. We just have to look for the strength.
Mittal, Chiraag, Vladas Griskevicius, Jeffry A. Simpson, Sooyeon Sung, and Ethan S. Young. "Cognitive adaptations to stressful environments: When childhood adversity enhances adult executive function." Journal of Personality and Social Psychology 109, no. 4 (2015): 604.