Exercise and health: Practice with mediators

Exercise is good for us. Brain-based mediators help explain why. Photo: muse studio/Shutterstock

This summary of exercise research, written by a journalist for the New York Times, is a good opportunity to practice diagramming mediators: How exercise strengthens your brain.

Here is one passage from the article:

Exercise offers short-term boosts in cognition. Studies show that immediately after a bout of physical activity, people perform better on tests of working memory [...]. This may be in part because movement increases the release of neurotransmitters in the brain, most notably epinephrine and norepinephrine.

“These kinds of molecules are needed for paying attention to information,” said Marc Roig, an associate professor in the School of Physical and Occupational Therapy at McGill University.

A mediator is an explanation for why two variables might be associated. In this example, the two original variables are exercise and working memory. You can think of the author as saying this:

But then the author explains why these two variables are associated. They explain that the reason--the mediator--is the release of epinephrine and norepinephrine. We can diagram this particular mediator argument like this:

The argument suggests that exercises leads to the release of epinephrine and norepinephrine, which leads to improvements in working memory.

a). Now try it yourself with another passage. First, read to identify the two core variables. Draw them in a diagram like the first one, above. Next, redraw the diagram by adding the mediator to it. To give you a hint, I've bolded the key variables in the quoted text. (You can check your answer to this one by scrolling down).

The neurotransmitters dopamine and serotonin are also released with exercise, which is thought to be a main reason people often feel so good after going for a run or a long bike ride.

b) Here's another example. Read this passage to identify the two core variables (you'll notice they're similar to previous examples). Next, redraw the diagram adding the mediator to it. To give you a hint, I've bolded the key variables in the quoted text:

It starts with the muscles. When we work out, they release molecules that travel through the blood up to the brain. Some, like a hormone called irisin, have “neuroprotective” qualities and have been shown to be linked to the cognitive health benefits of exercise, said Christiane Wrann, an associate professor of medicine at Massachusetts General Hospital and Harvard Medical School who studies irisin.

c) And here's one more to try:

The hippocampus, an area important for memory and mood, is particularly affected. “We know that it shrinks with age,” Dr. Roig said. “And we know that if we exercise regularly, we can prevent this decline.”

Exercise’s effect on the hippocampus may be one way it helps protect against Alzheimer’s disease, which is associated with significant changes to that part of the brain.

Not everything is a mediator, of course. The Times article also includes this passage, which depicts a moderator:

Once [key signaling molecules] are in the brain, other chemicals are released locally. The star of the show is a hormone called brain-derived neurotrophic factor, or B.D.N.F., that is essential for neuron health and creating new connections — called synapses — between neurons. “It’s like a fertilizer for brain cells to recover from damage,” Dr. Voss said. “And also for synapses on nerve cells to connect with each other and sustain those connections.”

A greater number of blood vessels and connections between neurons [caused by exercise] can actually increase the size of different brain areas. This effect is especially noticeable in older adults because it can offset the loss of brain volume that happens with age.

For your general enlightenment, here's a diagram of this moderator, using the diagramming conventions in Chapter 9: