How Stress Gets Under the Skin: Q&A With Neuroscientist Bruce McEwen

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A professor of neuroscience at Rockefeller University, Bruce McEwen investigates how stress affects the mind and brain.

He has published over 700 research papers exploring the ways that stress hormones can both damage the brain and lead to beneficial growth. TIME spoke with him recently about stress and health.

What are some common misconceptions about stress?

I’ll start with several pet peeves: that all stress is bad for you and that cortisol [a stress hormone] is bad for you because it’s easy to measure as a marker of stress. These stress systems were put there to help the body adapt and survive. They have a good side and a bad side.

That’s the essence of [what I have labeled] allostatic load:  these systems, which help us adapt and survive can also cause problems when they are overused. [That idea] gets away from the use of the word stress, but when we talk about stress, there’s good stress and toxic stress.

What is good stress?

Good stress is rising to a challenge, feeling exhilarated when your body and brain are working properly to help you do so.

And toxic stress?

It’s intolerable stress. When you lose your job and you’ve got friends and enough material and social support, you can weather it and come out strong.

[But] toxic stress is where bad things happen, perhaps because you don’t have the inner or external resources [needed to cope] and perhaps because you have had early life adversity, which makes you more vulnerable to adverse outcomes.

And toxic stress can lead to inflammation?

[Yes]. Inflammation in the brain [can] impair factors that lead to growth and new connections.  You can see how a vicious cycle would develop.

On the other hand, don’t many of the people who have difficult childhood experiences remain resilient and able to cope with stress?

It’s very important to separate that out. You’ve got the family, the caregiver and child relationship, which, if it’s consistent over time and doesn’t involve lots of up-down swings toward the kid and there is stability within the family, even in bad external environments, children can do well.

It’s amazing that children do find brothers, sisters, aunts, uncles, neighbors to find steady guidance. [Even] among kids who have not, there are these examples of kids who manage to survive.

So what increases the risk for problems like post traumatic stress disorder (PTSD)?

One of the greatest risk factors is often, as a result of early life adversity, [that] a child develops low self esteem and doesn’t have the ability to control [his stress response]. Vulnerability to problems like substance abuse and PTSD or depression comes with [adverse childhood experiences] but it doesn’t happen in everybody and we have to acknowledge that there are genes and variations that confer increased or decreased risk for this kind of outcome.

But it’s not just a matter of whether certain genetic mutations are present or not. The effects of some genes seem to depend on the environment in which children are raised. So, for example, these genes may make people smarter or kinder if they are activated in a good environment, while they might increase the risk of problems like depression or aggression if they are present in a chaotic one.

That’s the whole area of risk-reactive alleles or variants of genes that are risky [in some situations] but in a nurturing environment lead to better than average outcomes.  They have been called orchid and dandelion genes.

So, the orchids thrive in a hothouse designed for them— but wilt otherwise— while the dandelions are okay anywhere?

[Yes]. And another aspect is epigenetic factors. [Research on them] is just being to proliferate, and explores how modifications of the ability of genes to be expressed because of chemicals in the environment, but also because of experiences [can] begin to provide an understanding of the mechanisms underlying some of these phenomena.

The orchid and dandelion idea seems to suggest that some people’s talents or best qualities are forever lost if they have the wrong childhood: is that really the case or can they recover later?

That’s where you come into the area of plasticity, that’s newly recognized.  It seems likely [that they can recover] and there is some evidence that the reactivity of those alleles not only determines the outcome in good or bad [early] environments but also confers greater ability for plasticity later if you can find the right intervention.

Based on animal studies, can things like food deprivation and antidepressants also promote neurogenesis or growth?

[Yes] and that can also be mimicked by putting cortisol in the drinking water every other day.  That same [stress hormone] which we often think of as the bad guy may be facilitating the plasticity.

But you have to direct it. A lot of people think of [the antidepressant] Prozac as being like penicillin that is automatically going to cure depression. But in the same bad environment, it may lead to suicide or homicide. You have to target it and so when a GP hands out Prozac and someone goes home to a lousy environment, it’s no surprise that depression doesn’t improve.

Can exercise also promote the growth of new brain cells and connections between cells?

The poster child of the ability to change the brain is work on exercise. If you take sedentary people in their 60s and they start to walk  an hour a day, five days a week, the hippocampus gets larger.

Mindfulness-based stress programs can also cause [these kinds of] brain changes.

We often think about exercise and meditation being the best ways to fight stress, but what about social support?

[It’s very important]. One example is that when rats living together in stable social hierarchies are [given a] running wheel, exercise stimulates neurogenesis.  But if they are living in isolation, [and] alone, exercise does not stimulate it as much, if at all.

The two are very much synergistic. Our autonomic function and parasympathetic balance is very much influenced by social connections.

There is a balance between the parasympathetic nervous system [which is calming and influenced by warm social contact and things like meditation] and the sympathetic system, which increases inflammation and increases  heart rate and blood pressure.  You want to have the proper balance.

Of course, not all social contact is beneficial, such as the toxic stress that can come from being on the bottom of a social hierarchy.

That can be seen in studies on baboons. The subordinate animal is continually watching and can be attacked from anywhere. The dominant has to watch for a few enemies, but generally has it under control. The subordinate has the posture of low self esteem.

In human terms, the whole idea is that, well, this is why there is a subjective  socioeconomic status (SES) ladder. It’s people’s perception of where they stand that is a predictor of health outcomes.

The lower you are, the more resentment there is and it’s that perception that drives things like a sense of autonomy and other factors [that can determine your response to stress].  It’s also history: people in lower SES groups are more likely to have had adverse childhood experiences and are living in [lousy] neighborhoods where there is not access to good food, no safe places to exercise and there’s chaos and noise all the time. It’s a vicious cycle.

But it’s where you perceive yourself that matters.  The brain is the key because it perceives and decides what is stressful in the traditional sense of the word and regulates behavior and physiology.

There are buffering factors. [For example] a person may be a janitor but is the deacon of his church and has a wonderful family, and that buffers [the effect]. And perception is as good [a measure] as objective SES.

So what else can we do to fight toxic stress?

Many of the obvious things we’ve talked about. Be physically active, get a good diet, [get] adequate sleep, [create] social support, have a good hobby, meditat[e].  All of these things really are common sense and now we know they do have the benefits of improving our brain architecture.

I think that’s the bottom line. But the bigger question has to do with the social environment we live in, which is determined by the policies we set and politics. The pressure is on us for, ‘faster, faster, faster.’  They’re all working against what our bodies were intended to do. Spend more, do more, faster: that just doesn’t work.

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