Healthy Brain, Happy Life (17 page)

TAKE-AWAYS: THE BRAIN–BODY CONNECTION

•  The brain–body connection is the idea that your brain, including your thoughts, can affect your body (for example, thinking positive thoughts about a healing injury or recovery from the flu can speed the process), and conversely changes in your body (increased or decreased movement, for example) can affect your brain.

•  Intentional exercise happens when you make exercise both aerobic (movement) and mental (with affirmations or mantras). You are fully engaged in the movement and trigger a heightened awareness of the brain–body connection.

•  Intentional exercise can boost your mood even more than just exercise alone.

•  You can make any exercise intentional by adding affirmations or mantras to your workout.

•  Other brain areas involved in the regulation of mood include the hippocampus, amygdala, autonomic nervous system, hypothalamus, and the reward system.

•  Exercise enhances mood by increasing brain levels of the neurotransmitters serotonin, norepinephrine, and dopamine as well as increasing the levels of the neurohormone endorphin.

•  Positive affirmations have been shown to boost mood but the neurobiology underlying this behavioral change is not yet understood.

•  Just one minute of power poses decreases the stress hormone cortisol, increases testosterone, and results in people performing better in interview situations, suggesting that power poses should be used to prepare for important talks, presentations, and interviews.

BRAIN HACKS: FINDING THE EXERCISE THAT’S RIGHT FOR YOU

Are you currently in search of an exercise that will motivate you to get up off the couch and move your body on a regular basis? An exercise like intenSati really upped my dedication and enjoyment of exercise. The trick is to search out that particular form of exercise that you enjoy the most. There may be lots that you don’t enjoy, but find the one that really makes you feel great. Here are some avenues to explore:

•  If you love the outdoors and that wonderful sensory experience of nature, then definitely choose an activity like hiking, walking, or biking outside.

•  You can help enhance any workout with the music that makes your toes tap. Spend some time exploring an online music store, virtual radio app, or a music video station on YouTube and find those songs for yourself. I know for me a great song can make me start moving when I thought I was done for the day.

•  If you love working out with others, find some friends to exercise with or make new workout buddies at a gym.

•  For me, a great instructor can make me work out much harder and have much more fun than I would have on my own. See if you can find an instructor like that and take his or her class.

•  If you already like to do things like dance or ski or hike, then incorporate those into your regular workout schedule.

And finally, just keep this in mind: If you are learning a new exercise, don’t expect it to give you that endorphin high the very first time you do it. You need to develop a certain level of expertise in an activity before you can really start feeling that exercise high. So if you don’t feel it at first, but enjoy the exercise, stick with it and wait until you develop more skill. The high will come. Just trust your gut.

THE BIRTH OF AN IDEA:
How Does Exercise
Really
Affect the Brain?

A
s I neared the deadline for yet another science grant application to NIH (something I spent a great deal of time on as a science faculty member), I was becoming aware that my writing was going well—unusually well. My daily writing sessions were much more productive and even
enjoyable
compared to the stress-filled sessions of the past. Whereas it usually took me a week to write just one section of a grant application, I was now drafting more efficiently, fine-tuning more quickly, and enjoying the process a whole lot more. My attention was more focused and my thinking more clear. I made deeper, more substantive connections between my ideas and was doing so far sooner in the process than usual. This is when I began to suspect that there was a relationship between the regularity of my workouts and my supercharged grant-writing sessions. The writing just went more smoothly during a week when I exercised more than three or four times, compared to weeks when I slacked off and went to the gym only once or twice.

What was going on here? I realized that without knowing it, I had just conducted an experiment on myself! I varied my exercise regime (some weeks four or five exercise sessions and other weeks only one or two) and found that only with a higher frequency of exercise did I notice enhanced attention and the ability to make new and better thought “connections” in my writing. While focused attention is known to depend on the prefrontal cortex, the ability to make new connections or associations is thought to depend on the hippocampus.

This was fascinating! I knew there had been lots of progress in our understanding of how exercise could affect brain function, but I had not kept up with that literature—too busy getting tenure, I guess. So when I noticed these changes in myself, I dove into that neuroscience literature to see what was new.

What I found was an active and growing body of research that was deep into identifying all the different ways aerobic exercise affects brain function. These studies documented a range of anatomical, physiological, neurochemical, and behavioral changes associated with increased aerobic exercise. But the biggest surprise I got when exploring this literature was that one of the founders of this whole line of research was a scientist with whom I was very familiar: Marian Diamond.

It seemed like a sign.

It turns out that our understanding of the effects of exercise on brain function had its origins in the original studies that Diamond did on brain plasticity and the effects of raising rats in enriched environments on brain function. As I mentioned in Chapter 1, those early studies showed all sorts of brain changes when rats were raised in the enriched environments: The animals developed a thicker cortex because of the more extensive branching of the dendrites, more blood vessels, and higher levels of particular neurotransmitters like acetylcholine as well as increased levels of growth factors like brain-derived neurotrophic factor (BDNF). Acetylcholine was the very first neurotransmitter ever discovered, and the brain cells that use it send signals throughout the cortex as well as to the hippocampus and amygdala. Acetylcholine is an important modulator of learning and memory, and studies show that drugs that interfere with the action of acetylcholine result in memory impairments in both animals and humans.

BDNF is a growth factor in the brain that supports the survival and growth of neurons during brain development as well as synaptic plasticity and learning in adulthood. Not only that, but a truly exciting finding was reported in the 1990s, when researchers in California demonstrated that rats raised in an enriched environment had more new neurons in their brains than other rats. This process is called neurogenesis. While lots of new brain cells are born during our early development period (from infancy through adolescence), there are only two places in the brain where new brain cells are created in the adult brain. One is the olfactory bulb, the part of the brain important for sensing and processing smells (see Chapter 1), and the second is my old friend the hippocampus. But even more significant is that new brain cells are formed on a regular basis in the hippocampus of adult rats. The enriched environment also was linked to a higher number of hippocampal brain cells (but not in the olfactory bulb). Other studies showed that rats raised in enriched environments and that had more new hippocampal cells also performed better on a range of different learning and memory tasks, suggesting that all these new neurons were helping the rats learn and remember better.

But then neuroscientists began to wonder what it was about the enriched environment that was causing all these striking brain changes. Was it the toys? Was it the gaggle of other rats to play with? Maybe it was all that running around that the rats did in the Disney World–like environment. When scientists tested these factors systematically, they discovered that one contributed to the majority of the brain changes seen with an enriched environment: exercise. They found that all they had to do was give a rat access to a running wheel, and they would see most of the brain changes they observed in rats that were raised in the enriched environment. Indeed, this line of research in rodents has shown us how exercise affects the brain at the molecular, cellular, brain circuit, and behavioral levels.

We now know that exercise alone can actually double the rate of neurogenesis in the hippocampus in rodents by increasing the total number of new neurons that are born, enhancing their survival (many of the new cells die) as well as speeding their maturation into fully functioning adult brain cells. These new neurons are not born just anywhere in the hippocampus but in only one specific subregion, called the dentate gyrus. When I read this, I felt like going to the gym and working out even harder! Exercise in rodents also increases the number of dendritic spines on the neurons in the dentate gyrus; these spines are budlike appendages on the neurons’ dendrites, the branchlike structures where neurons receive information. Exercise also increases the total length, complexity, and spine density of the dendrites. Thus it is not surprising that the total volume of the dentate gyrus also increases with exercise. Spine density in other regions of the hippocampus and the adjacent entorhinal cortex (which I studied as a graduate student) is also increased significantly by exercise. Spines are where the axon of one neuron contacts the dendrites of the next neurons; the more spines on a neuron, the more communication is happening. Another robust change researchers confirmed with exercise alone was the growth of new blood vessels throughout the brain (including in the hippocampus), which is called angiogenesis.

The physiological properties of the rodent hippocampus also change after exercise. This physiological phenomenon is called long-term potentiation (LTP), which is a long-lasting change in the electrical response between two groups of neurons. We study this change by stimulating the connections between the two groups of cells in the hippocampus with an electrical current. If you stimulate one of the pathways within the hippocampus with multiple fast bursts of electric current this will increase the response you get from a weak electrical stimulus to that pathway compared to the same weak stimulus given to the pathway before the burst of current. LTP is widely considered to be a major cellular mechanism for learning and memory. LTP is enhanced in the brains of rats that have been exposed to exercise. One key factor that might be contributing to these effects is the increase in BDNF because we know that BDNF can also enhance LTP. But BDNF is not the only factor that increases with exercise. As I mentioned in Chapter 4, in addition to all these anatomical and physiological changes, exercise also increases the brain levels of serotonin, norepinephrine, dopamine, and endorphins.