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Lecture 2

Listen to part of a lecture in a health science class.

We’ve all heard that there are health benefits to regular exercise. It’s hard even to know where to begin.Increased strength, a sense of well-being, weight maintenance, a healthy heart and cardiovascular system…Need I go on?

Now we’re hearing that exercise also has a positive effect on our high-level intellectual abilities.

There are a few hypotheses that may explain how exercise affects our brain. But before we get into that I need to talk a little bit about neurogenesis. Neurogenesis is the creation of new neurons, nerve cells in the brain.

Now, maybe you’ve heard that the human brain doesn’t generate new neurons after fetal development, that the neurons you have when you are bom are all you’ll ever have, unlike what’s true of cells in most tissues, which are generated and replaced throughout life.

But some decades ago, research on the ability of adult songbirds to learn new songs changed that whole paradigm. The research showed that in adulthood, the songbirds, brains created new neurons and that these new cells helped them remember how to sing new songs. These findings on songbirds open up the question of whether the same processes that occur in birds also occur in humans.

And subsequent research confirmed that the adult human brain indeed generates new neurons in the memory center of the brain.

But how exactly does exercise fit in here?

Well, probably the most studied hypothesis out there proposes that exercise increases the production of important proteins in the brain. One such protein is called brain-derived neurotrophic factor, or BDNF. Brain-derived neurotrophic factor helps neurons grown, multiply, connect, and transmit signals.

We’ve always known that it serves this function during fetal development, but does it play a role in the proliferation of adult neurons as well?Well, let’s consider what some animal studies indicate.

In one important rat study, brain signals and responsiveness to those signals were enhanced within just seconds after rats were administered doses of BDNF.And physical activity in rats, even just a few minutes of swimming, has been shown to increase BDNF levels.

Yes, Susan?

Uh, that study was done on rats.

Well, it’s true that the direct connection between BDNF, physical exercise, and brain performance in people, hasnl been proven yet, but the sheer numbers of studies that indicate a connection in animals say a lot, in my view.

And exercise does seem to have an effect on the human brain.

The research done with brain-imaging techniques shows that the brains of people who exercise are much denser compared to those who dont, suggesting that neurons are branching and making connections with other neurons.

Also, in clinical studies involving active and inactive adults, the active adults scored much higher on cognitive tests that measure high-level thinking skills than inactive adults did.

But I’ve always thought that doing crossword puzzles, and, like, reading a lot, was important if you wanted to maintain your thinking abilities, you know, that you need to stay mentally stimulated and learn new things.

Yes, it seems that gaining knowledge or abilities is another key. While it’s true that thousands of new neurons are produced in the brain’s memory center each day, and that exercise promotes their generation, those new neurons will just die off if they are not being used for anything.

Animal studies have shown a correlation between acquiring new skills and new neurons actually surviving in the brain. It seems to be a use-it-or-lose-it kind of thing. So, good point!

Yes, Matt?

I was just wondering how much exercise do we need to keep our brains making neurons. I imagine the more the better, right?

Well, interestingly, some studies suggest that less is more here. You see, there’s a particular stress hormone that’s elevated in response to all methods of exercise, but more so with more intense regiments. Stress hormones have been implicated in reducing BDNF levels and can also create a cascade of other problems in the human body.