Stress Really is Bad

We all have a little stress in our lives. But after studying nerve cells in a banana-shaped area of the brain called the hippocampus, a hub for learning and memory, neuroscientists say chronic stress can have devastating effects on our brains.

Bruce McEwen, professor and head of the neuroendocrinology laboratory at the Rockefeller University, explains more about the hippocampus: “It’s a structure that is very important for remembering where you were and what you were doing when something important happened; in other words, providing context. For example, remembering where we were and what we were doing on September 11, 2001—that’s a function of the hippocampus. The reason that we remember that horrible day is that another brain structure very close to the hippocampus, called the amygdala, is a structure that reacts strongly to emotionally-charged events, either very positive or very negative events.”

McEwen and his team, who published their research in the February, 2003 issue of Nature Neuroscience, looked at the brain cells of both stressed and not-so-stressed mice, and found something interesting about the brains of stressed-out mice. “[Nerve cells] have these wonderful trees [with branches] that are called dendrites, places where other nerve cells make connections and transmit chemical signals,” says McEwen. These cells connect to each other at junctions called synapses. “When we look at these individual nerve cells from an animal that’s stressed or not stressed, we could see some very characteristic changes. For example, the branches become shorter and less branched, as a result of repeated stress. That means there are fewer synaptic connections, and it means these cells are not receiving as much information as they normally do. When you look at many of these cells you realize that many of the cells in this brain area called the hippocampus show this shrinkage after repeated stress.”

The hippocampus (in yellow).

McEwen’s team found the opposite was happening in the part of the brain that regulates fear and emotion, the amygdala . “With a chronic stress, neurons in the amygdala grow, they become larger,” says McEwen. “And there’s evidence that in depressive illness the amygdala may even become larger, and it certainly becomes more active.”

So, after exposure to chronic stress, if the cells in your hippocampus are shrinking, and the cells in your amygdala are growing, “you may have all sorts of anxieties and anger and fear, and yet you don’t have the hippocampus to help you connect it to where you were and what you were doing to make it specific. So you may have generalized anxieties as a result of this.”

This can also be looked at in the human brain using magnetic resonance imaging (MRI). “The living brain can be imaged while the person is awake and conscious,” says McEwen, “and you can actually measure the volume of the hippocampus in disorders like major depressive illness. If [a depressive illness] goes on for a long enough time, the hippocampus becomes smaller. We think it becomes smaller because the nerve cells are shrinking the way we originally saw it under the microscope.”

McEwen says that we could try to cope with stress by “going out and relaxing and enjoying a hobby, enjoying friends, exercising, going on a vacation, doing good stuff that will actually push our bodies in the right direction.”

Researchers advise that if you’re up against a situation that you cannot control, don’t keep it inside. Talk about it with friends and family or see a health professional. Funding for the research came from the National Institutes of Health.