Resilience, stress, and plasticity

Professor Bruce McEwen describes the interplay between reilience and stress, which can cause the brain to shrink or grow.

Then we talk about resilience. One of the things that we know, from our studies on the brain under stress (this is in animal studies), is that, in different parts of the brain, neurons shrink or grow – their dendritic trees either retract or expand. For example, in the amygdala, there is growth of dendritic trees as an animal is stressed and becomes more anxious. But in the hippocampus, there is a shrinkage of cells, and the animal doesn’t do as well in certain kinds of memory tasks. In the prefrontal cortex, there’s a shrinkage of nerve cells, and the animal, and actually some people studies as well, show that people become more inflexible in decision making. Now, all of these things, in the animal models at least, are reversible. If you turn off the stress and give time without stress, these neurons grow back to normal or shrink back to normal. However, and that’s the normal case; it’s kind of natural, if you have a very bad event, a tolerable stress, to become depressed or anxious. Say something happens where somebody is mugged or something and they have a traumatic stress experience and they’re anxious and wary, most people get over it and they come back to normal. Other people, however, who remain anxious, may develop what we call post-traumatic stress disorder, or, if they have a depressed mood, will develop a major depressive disorder. One way of looking at that is that this is a lack of resilience, a lack of the normal ability of nerve cells, even after they have shrunken to grow back, or after they’ve grown, to shrink back to their normal state. Then we have to either intervene with a drug or a pharmaceutical agent or with some kind of behavioral intervention, or a combination of both. So it’s that lack of resilience of a very plastic brain that actually may be the difference between whether somebody has an anxiety disorder that lasts for a very short time or a permanent, long lasting anxiety disorder.