A Scientific Look at the effects of exercise on the brain
According to John Ratey, M.D.’s 2008 book, Spark: The Revolutionary New Science of Exercise and the Brain, depression can be explained from an evolutionary perspective. We still don’t know what causes depression, but science has made great strides in understanding the brain’s activity surrounding emotions. As we’ve learned more about the biology of mood, we’ve also come to learn how aerobic exercise alters it.
A massive Dutch study of 19,288 twins and their families published in 2006 showed that regular exercisers are less anxious, less depressed, less neurotic, and more socially outgoing. An even larger Finnish study of 34,403 people in 1999 showed that those who exercise at least two or three times per week experience significantly less depression, anger, stress, and “cynical distrust” than those who exercise less or not at all.
From an evolutionary perspective, everything we do and that happens to us as human beings serves a purpose, or can otherwise be explained. The same can be said for our brain chemistry. We become happy when our circumstances are serving us and our survival, we become anxious so that we are motivated to change a threatening situation, and we become depressed in response to a prolonged situation that is unfavorable to our survival. We are not yet certain of what causes depression. However, we do now see depression as a physical alteration of the brain’s emotional circuitry. Norepinephrine, dopamine and serotonin are essential messengers that carry information across the brain’s synapses, but without good enough connections in place, these neurotransmitters can only travel so much. As far as the brain is concerned, its job is to transfer information and constantly rewire itself to help us adapt to our environment and survive. In depression, it appears that in certain areas, the brain’s ability to rewire and adapt is significantly stunted. According to John J. Ratey, M.D.’s 2008 book, Spark: The Revolutionary New Science of Exercise and the Brain, depression likely results
Health experts have long touted the role of exercise in preventing and treating diseases like heart disease, diabetes, and obesity — but for many people, the promise of a healthier body isn’t enough to get them (or keep them) moving. In Spark, John J. Ratey, MD, makes a compelling case for exercising to boost brain function — which may be far more motivating for some.
The author spells out the remarkable role that aerobic exercise plays in alleviating common conditions such as depression, anxiety, ADHD, and stress. He details the stabilizing and stimulating effect of exercise on hormones and neurotransmitters that affect learning, motivation, and mood — and how exercise combats the cognitive decline that comes with aging. Throughout the book, Dr. Ratey shares case studies and explains research to help you understand why exercise is critical for short-term and long-term brain function — and how exercise can even alter brain structure, stimulating the growth of new brain cells and increasing the size of brain areas responsible for high-level thinking.
We all know by now that exercise is good for us—mind and body. Our physicians prescribe exercise for preventing and treating everything from obesity, to heart disease, to depression. Unfortunately, many of us remain sedentary until we are sick and tired of feeling bad, i.e., actually suffering from depression or anxiety. Exactly how exercise affects our brain chemistry has been and remains up for debate. John J. Ratey, M.D. presents in his 2008 book, Spark: The Revolutionary New Science of Exercise and the Brain, compelling evidence and explanation for the connectivity theory of depression, and how aerobic exercise can have similar or equal effects as antidepressants. He presents clinical studies suggesting that exercise can actually alter brain structure, stimulating the growth of new brain cells and increasing the size of brain areas responsible for mood, attention and high-level thinking.
We have known that in the brain, the amygdala is central to our mood and emotional life, and the hippocampus is responsible for memory. In 1996 Yvette Sheline of Washington University in St. Louis found that the hippocampus of depressed patients was 15 percent smaller compared to that of controls. She also found evidence that the degree of shrinkage was directly related to the length of depression, and this was big news. It might explain why so many depressed patients experience learning and memory trouble, and why mood deteriorates in Alzheimer’s, the degenerative disease that begins with the erosion of the hippocampus.
If you were to put a neuron in a petri dish and flood it with the stress hormone cortisol, its vital connections to other cells would retract, or die. This causes a communication breakdown, which, “in the hippocampus of a depressed brain, could partly explain why it gets locked into thinking negative thoughts—It’s recycling a negative memory, perhaps because it can’t branch out to form alternative connections” (Spark, p. 129).
Connectivity Theory explained:
As almost all we have become as humans serves an evolutionary purpose, depression is no exception. Psychologist Alexander Niculescu sees depression as a survival instinct to conserve our energy resources in an environment void of hope—“to keep still and stay out of harm’s way,” written in a 2005 article in Genome Biology. It can be viewed as a type of hibernation—as our emotional environment turns wintry, our neurobiology tells us to stay inside. Only, it tends to last longer than one season. It’s as though our entire being has said, “there’s nothing out there for me, so I may as well quit.” Thus, our neural connections literally die off, plasticity no longer occurs, and areas of the brain lose connection to one another. Depression shuts down our drive to sleep, eat, have sex, and generally look after ourselves on a primitive level.
It wasn’t until we were first able to see good images of the brain, that we really began to understand how exercise can reverse depression. In the early 90s, MRI scans showed us that the length someone was depressed was directly correlated to how eroded certain areas of the brain was—both white matter and gray matter, and particularly the areas of the amygdala and hippocampus, responsible for our emotional life and memory. In 1996 it was found the hippocampus of a depressed person was on average 15% smaller than that of a non-depressed person.
We also learned that new nerve cells are born every day in the hippocampus and possibly in the prefrontal cortex—two areas that are shriveled in depression. The shut-down that occurs in depression is thus a shut-down of learning at the cellular level. The brain loses the flexibility to think its way out of a hole.