“An apple a day keeps the doctor away.” With this unfortunate aphorism, my mother put me off eating apples for many years by associating them with: 1) doctors, and 2) things I’m really supposed to do. I felt similarly about exercise for many years: something I put off doing year after year despite the headlines telling me how good it would make me feel.

Russell Collins

Russell Collins

Maybe it’s just me, but I mention this because I am afraid that the revolution that is under way in our understanding of exercise and its relationship to happiness and well-being has been lost in the business-as-usual wave of self-help journalism. Exercise can profoundly change your moment-to-moment experience of life, it turns out, and since the accumulation of moments is pretty much what life is, regular exercise may be a hugely significant factor in everything you do: work, home, friends — all of it.

The biology behind this isn’t difficult, it’s just new, resting on new understanding in two areas: stress and neurogenesis, or the ability of the brain to grow new brain cells. Because each year brings new advances in the technology for looking inside our brains, we are in the midst of an explosion of knowledge about how the brain generates this process we call living or experience.

On one hand, we are just discovering that new brain cells can grow, either to accommodate or expand functionality, or to replace destroyed cells. And we are just beginning to see how that can change our attitude toward life. On the flip side, we are growing increasingly aware of the powerful effects of certain attitudes — both positive and negative — on the structure of our brains.

Let’s talk about stress. Like exercise, stress is often misunderstood. It’s not just that feeling you get when there are too many bills, or your boss yells at you, or you’re caught in traffic. In biology, a stressor is an external state change that results in a physiological response from a living system required to keep it in balance. Stress can be helpful or hurtful to your body’s performance.

Fortunately, our bodies are designed for most types of stress. The one kind of stress we are not built for is the kind that is produced by our attitudes or interpretations of situations (chronic worrying or anxiety, for instance), something seen in humans but not found elsewhere in the evolution of organisms. An overdue library book can’t cause a zebra stress (a fact memorialized by Robert Sapolsky in the title of his highly readable Why Zebras Don’t Get Ulcers). But it can be painful for you or me as we imagine the repercussions to, say, our friendly relationship with the librarian or mounting library fees. What’s worse, the stress of the overdue book can cause the production of chemicals that destroy brain cells, especially in an area of the brain called the hippocampus.

Many of the breakthroughs in our understanding of the hippocampus came from research on a legendary patient named H.M., or Henry Molison, who died just last year. For a half-century, Molison was studied by psychologists and neuroscientists trying to understand the function of the hippocampus and surrounding brain regions, which had been surgically removed from Molison’s brain. Though he functioned normally in most of the tasks of daily living, he couldn’t remember new experiences for more than a minute or so.

Brenda Milner, a neuroscientist who worked with him for many years after his surgery in 1953, recalled in a New York Times interview at the time of his death, “He was a very gracious man, very patient, always willing to try these tasks I would give him, and yet every time I walked in the room, it was like we’d never met.”

That sums up much of what we know about hippocampal function in memory; it seems to organize our impressions into narrative memories and send them off to other areas of the brain for long-term storage. A rat who is given a learning task and then injected with anesthestic in the hippocampus will not remember the task. But wait 30 days and anesthetize the hippocampus again, and the memory will be intact: It’s been safely transferred to the cortex. The stored memory carries with it the sensory data and emotional associations of the original experience, especially if these associations are fearful or negative.

So, the sights, sounds, smells, etc., that I associate with eating a Christmas turkey at Grandma’s last year might be packaged up by the hippocampus with a sense of where (Grandma’s dining room), when (the night before Christmas) and who (my brothers and sisters), then stored in a file drawer marked “really unpleasant experience,” because in the midst of dinner, Grandma choked on a pistachio shell and had to be rushed to the hospital. The “really unpleasant” part is actually filed nearby, in a related structure called the amygdala, which carries on a neural conversation with the more objective hippocampus to alert it to the dangerous or negative meaning of the memories (as psychologist Louis Cozolino writes in his book The Neuroscience of Psychotherapy, the amygdala will make us jump at the sight of a spider, the hippocampus will allow us to remember that this particular spider isn’t poisonous, so we shouldn’t worry).

This year, then, when Grandma calls to invite me for Christmas, the memory of Phoenix, the family and the pistachio shell returns, accompanied (courtesy of the amygdala) by the faint whiff of fear. Both the original event and the recent memory of it can cause me stress.

So, a stressful event may be taking a bite out of my happiness quotient both coming and going. First, stress causes the release of hormones that are toxic to cells in the hippocampus. A shrunken hippocampus may then be a direct or indirect cause of depression, especially the cognitive aspects of depression, such as feelings of guilt and worthlessness. This may well be because the hippocampus isn’t functioning well enough to modulate the fear messages of the amygdala, so my memory of Christmas is now overwhelmed by frightening messages causing me to feel bad. A helpless or hopeless depressive view of the world creates even more stress, of course, creating more hippocampal cell destruction and increasingly more and more negative assessments of life’s events — well, you get the point.

(I feel better now, having recounted the whole Christmas story. This could be an effect of what cognitive scientists call “reconsolidation”: the newly remembered event gets repackaged and stored again, but this time with less fearful or negative associations. Could this be how psychotherapy works in the brain?)

What does any of this have to do with exercise or Prozac? We’re getting there.

If you’ve ever taken an antidepressant such as Prozac or Lexipro, or know anyone who has, you know about the famous delay that occurs between the time you start taking it and the time you actually get the beneficial effects. There are a number of theories about why this happens. One possibility is that the neurotransmitters that are made more available in the brain by the antidepressant actually promote new cell growth in the hippocampus. Until very recently, it was believed that the brain cannot generate new neurons or cells. But we now know that there are stem cells present in the structure of the hippocampus that are activated, divide and give rise to new cells in a way that is likely related to the medication. This may allow new cells to regenerate fast enough so that the affected areas of the hippocampus regain much of their functioning over a two- to six-week period, the amount of time it takes for the mood effects of the medication to kick in. Should that happen, my memories of Christmas at Grandma’s (or anything else) might not make me feel so bad about life.

(Interestingly, this seems to work in reverse as well. Certain kinds of psychotherapy that have us consciously reinterpret events in a less depressing light have been shown to result in increased density in the hippocampus, probably coming from new cell growth.)

If the hippocampus is able to regenerate cells and regain its normal functioning, in other words, this could positively affect the way events are encoded, stored and retrieved, and even reconsolidated as less threatening memories. Prozac and other antidepressants, most neuroscientists now believe, may be helping new cells grow, and there is some evidence that the new cells are less dialed in to old associations of negativity and fear.

Now, the exercise part.

Exercise is now believed to have almost identical effects in promoting new hippocampal growth, just as antidepressant medications do. This may be why, in some experiments, exercise affects mood positively in moderately depressed clients about the same rate as the medication. In recent experiments with rats, new brain cells generated by exercise have been at least provisionally demonstrated to provide significant antidepressant effects. In addition, moderate exercise for three or four weeks (about the time it takes to rebuild the cells) seems to significantly reverse the effects of aging on long-term memory formation, which translates not only into heightened mood, but a noticeable reverse in age-related cognitive decline (remembering people’s names, for instance, in one recent experiment). These effects will continue as long as you keep up the exercise routine, as will the positive feedback effect of hippocampal health creating positive experience and memories, supporting continued neurogeneration, etc.

The discovery of regenerating stem cells in the hippocampus, and its relationship to exercise, is no small thing. It opens the way to new therapies that enhance nature’s regenerative capabilities to combat depression and the ravages of old age. It will certainly, in time, produce methods for increasing certain kinds of intelligence, perhaps through specialized training or psychotherapy rather than medication. It’s part of a medical revolution that will bring unimaginable health benefits, if not to my generation, then to my children’s. Most importantly, to me, it resolves our understanding of mind and body as a single integrated system that creates our experience of life.

For those of involved in the mental health profession, as therapists or social workers or psychiatrists, this is both a challenge and an opportunity to rethink our understanding of our enterprise, and open up whole new vistas in the search for human happiness.

— Russell Collins is a Santa Barbara psychotherapist and divorce mediator. Click here for more information.