Spark: The Revolutionary New Science of Exercise and the Brain

Chapter Two (Learning: Grow Your Brain Cells)

We now move from a case study to more detailed explanation of the impact of exercise on the brain. I’m very heartened to see that Ratey doesn’t hesitate to use big words with lots of syllables while explaining the science. While reading popular science books, I’ve seen both experts oversimplifying for the public (hello, Michio Kaku) and laypeople oversimplifying by accident; this is a tough balance to strike and my first impression is that Ratey has managed admirably.

“Darwin taught us that learning is the survival mechanism we use to adapt to constantly changing environments.”  So far so good; this is one of the primary evolutionary advantages we humans have.

“What we now know is that the brain is flexible, or plastic in the parlance of neuroscientists––more Play-Doh than porcelain.” I spent two years assisting with neuroplasticity research, so this will be an interesting walk down memory lane.

“The way it works is that an electrical signal shoots down the axon, the outgoing branch, until it reaches the synapse, where a neurotransmitter carries the message across the synaptic gap in chemical form. On the other side, at the dendrite or the receiving branch, the neurotransmitter plugs into a receptor––like a key into a lock––and this opens ion channels in the cell membrane to turn the signal back into electricity. If the electrical charge at the receiving neuron builds up beyond a certain threshold, that nerve cell fires a signal along its own axon, and the entire process repeats.” Seriously, major points here for explaining the theory behind the argument. A lot of pop science books I’ve read gloss over the science, which makes the author’s argument sound weak and hand-wavy (and gives the impression that they think their audience is full of idiots.)

“About 80% of the signaling in the brain is carried out by two neurotransmitters that balance each others affect: glutamate stirs up activity to begin the signaling cascade, and gamma-aminobutyric acid (GABA) clamps down on activity.” I once made cupcakes for my lab with chocolate GABA and glutamate decorations, which I think you’ll agree makes me highly qualified to comment on this research.

I would like to add an aside here and say that the Apple dictation function is seriously impressive and making this entire process much easier on my wrist. Points for Apple.

“Only a mobile creature needs a brain, points out New York University neurophysiologist Rodolfo Llinás…he uses the example of a tiny jellyfish-like animal called a sea squirt…For most of its life, it looks much more like a plant than an animal, and since it’s not moving, it has no use for its brain.” Okay…but then how do you explain brain coral?

“As the CEO of the brain, the prefrontal cortex has to stay in close contact with the COO–-the motor cortex–as well as many other areas. The hippocampus is something like the cartographer…” We now have a CEO, a COO, and a cartographer. It’s good to know the brain is actually Rand McNally.

“Imagine if we had to stop and think to process every thought and to remember how to perform every action. We’d collapse in a heap of exhaustion before we could pour our first cup of morning coffee. Which is why a morning run is so important.” That is a non sequitur for the ages.

I should note that I’m making silly comments here because the opening of this chapter is essentially an overview of the last century of research into synaptic plasticity. It’s fascinating stuff, but there’s not a whole lot for me to quibble with.

“They use a rodent size pool filled with opaque water to hide a platform just decent surface in one quadrant. Mice don’t like water, so the experiment was designed to test how well they remember, from an earlier dip, the location of the platform–their escape route.” You know, I’ve always heard research is sink or swim.

“And it seems that cells spawned during exercise are better equipped to spark LTP.” I don’t know if you can actually draw this conclusion: exercise does promote neurogenesis, exercise also promotes production of BDNF, and BDNF is necessary for LTP, but the studies cited in the book don’t show anything about cells specifically generated as a result of exercise producing more BDNF.

“One thing scientists know for sure is that you can’t learn difficult material while you’re exercising at high intensity because blood is shunted away from the prefrontal cortex and this hampers your executive function.” It’s also really hard to hold a textbook while you’re running. Not that I would know anything about that.

“As for how much aerobic exercise you need to stay sharp, one small but scientifically sound study from Japan found that jogging thirty minutes just two or three times a week for twelve weeks improved executive function. But it’s important to mix in some form of activity that demands coordination beyond putting one foot in front of the other. Greenough worked on an experiment several years ago in which running rats were compared to others that were taught complex motor skills, such as walking across balance beams, unstable objects, and elastic rope ladders. After two weeks of training, the acrobatic rats has a 35 percent increase of BDNF in the cerebellum, whereas the running rats had none in that area. This extends what we know from the neurogenesis research: that aerobic exercise and complex activity have different beneficial effects on the brain. The good news is they’re complementary. ‘It’s important to take both into account,’ says Greenough. ‘The evidence isn’t perfect, but really, your regimen has to include skill acquisition and aerobic exercise.'” I have to give Ratey some credit here, because he has the entire bibliography for this book posted on his website. More pop science books should be this careful about listing all of their sources. That said, he doesn’t actually cite his sources in the traditional sense–he just lists all of the sources he referenced, without footnotes or anything. This means identifying the individual studies he refers to takes a bit of hunting. I couldn’t find any reference to Greenough’s experiment in the bibliography, which makes me think it was unpublished. While it sounds like interesting research, I’m dubious about using unpublished research as a source because the reader can’t refer back to it to do their own analysis. I did look up the jogging study; according to the abstract it involved fourteen participants divided into two groups, but I don’t have access to the full article so I’ll have to take Ratey’s word that it was scientifically sound.

Chapter Three (Stress: The Greatest Challenge)

The next chapter unfortunately focuses less on synaptic plasticity. It begins with an anecdote about a woman who starts drinking wine to cope with the stress of a kitchen remodeling, and then kicks the habit by jumping rope instead of drinking wine when she gets stressed. It sounds a little silly, but I can see the merit in it: since the wine-drinking was a mechanism for coping with the feeling of not being in control of her house, doing another activity she can completely control would be a reasonable way to restore a sense of stability.

“Most people use the word [stress] indiscriminately for both cause and effect. That is, the stress the world exerts upon us––’There is a lot a stress at work right now’––as well as the feeling that we get inside when everything seems like too much: ‘I’m so stressed, I can’t think straight.'” Clearly these are both imprecise, as a stress is a force applied over an area and has units of pascals.

“Stay there too long, and we’re talking about chronic stress, which translates emotional strain into physical strain.” But strain is a dimensionless quantity that indicates the degree of deformation…I’ll stop.

“The amygdala’s job is to assign intensity to the incoming information, which may or may not be obviously survival related.” It’s also to be the elected queen and then senator of Naboo, but that’s secondary.

“The finding initially alarmed scientists because the stress hormone had been shown to be toxic to brain cells in a petri dish.”

“The human body is built for regular physical activity, but how much? In a 2002 article in the Journal of Applied Physiology, researchers studied this very question, by looking at our ancestors’ pattern of physical activity, which they call the Paleolithic rhythm. From the time Homo sapiens emerged two million years ago, until the agricultural revolution, ten thousand years ago, everyone was a hunter–gatherer, and life was marked by periods of intense physical activity followed by days of rest… Our average energy expenditure per unit of body mass is less than 38 percent of that of our Stone Age ancestors… Paleolithic man had to walk five to ten miles on an average day, just to be able to eat.” That last sentence is not consistent with days of intense physical activity followed by days of rest. I’m not quibbling with humans being designed for a very different lifestyle than our modern one, but it’s important to be consistent with how you characterize that historic lifestyle.

“Our body is calling for more glucose, and simple carbohydrates and fat––like those glistening in a box of Dunkin’ Donuts––are readily converted into fuel.” Yep, the author’s definitely from Massachusetts.

“In many of his experiments, Mattson uses dietary restriction to cause mild cellular stress–-there isn’t enough glucose to produce adequate amounts of ATP––and he’s found that mice and rats that are given a third of their normal calories live up to 40 percent longer than average.” I’m going to go ahead and take this opportunity to give a shout–out to my dad, who researches calorie restriction and intermittent fasting. I’m pretty sure I remember him showing me this study.

“Prenatal rats whose mothers are subjected to repeated stress grow up to have a lower stress threshold than their normal counterparts.” I know I joked earlier about the definition of stress, but there’s a reason it’s important to be scrupulously clear with terminology. I have no clue if this is referring to environmental stress, oxidative stress, or metabolic stress.

“Other studies show that employees who exercise regularly have fewer sick days.” I’m not surprised that there’s a correlation here, but the more interesting data would be if they actually showed causation. The book doesn’t clarify which it is.

To conclude the chapter, I find it very odd that Ratey decided to use his “stress” chapter to discuss both broad emotional stress and small-scale cellular stress. The two are related, but the connection is not as apparent as he seems to think, and adding in discussion of cellular stress ends up making the chapter hard to follow.

Chapter Four (Anxiety: nothing to panic about)

“In fact, 104 studies on exercise and anxiety reported between 1960 and 1989, showed that exercise alleviates anxiety, but most of them didn’t meet the randomized, double-blind, placebo-controlled trial criteria necessary for scientists to count them as medical fact.” I can’t tell if this is a criticism or not, because that’s exactly how this is supposed to work. With this many studies, though, this would have been a good opportunity for a meta-analysis.

“ANP is secreted by heart muscles when we exercise, and it makes its way through the blood-brain barrier.” It doesn’t actually say anywhere what ANP stands for, so I am forced to assume it is Acadia National Park.