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Marathons and Memory

By cortex on July 30, 2009.

The Neurocritic has a fascinating summary of a recent paper investigating different types of memory in marathon runners. Why marathoners? Because completing a 26.2 mile race is an insanely arduous exercise, and leads to the massive release of stress hormones such as cortisol. Here are the scientists:

Indeed, cortisol levels recorded 30 min after completion of a marathon rival those reported in military training and interrogation (Taylor et al., 2007), rape victims being treated acutely (Resnick, Yehuda, Pitman, & Foy, 1995), severe burn injury patients (Norbury, Herndon, Branski, Chinkes, & Jeschke, 2008), and first-time parachute jumpers (Aloe et al., 1994).

But before we get back to the marathoners, a quick discussion of human memory. There are two distinct types of memory, which rely on different pathways in the brain. Explicit memory involves the recollection of discrete facts, events, names, faces, etc. It's a conscious process and is largely modulated by the hippocampus. (This was first discovered by studying patients with hippocampal lesions who turned into amnesiacs.) The second type of memory is implicit, largely unconscious and allows us to act based on previous experiences without taking the time to recall discrete memories. Think, for instance, of riding a bicycle. You have an implicit, procedural memory of the motor movements required to balance on two skinny wheels. As a result, you don't have to relearn the movements, or even consciously consider them, every time you go for a ride.

It has long been known that stress disrupts explicit memory, which is why it's not good to be too stressed when taking a test. The scientists hypothesized that finishing a marathon would wreak havoc on our explicit memory system, while leaving implicit memory largely intact. (There are probably good evolutionary reasons for this. It's not useful to forget how to throw a Pleistocene spear when being chased by a bear; if stress disrupted our procedural memory, we'd all be dead by now.)

The experiment itself was straightforward: 261 marathoners running in either the New York City Marathon or the Boston Marathon were given two different verbal memory tests, targeting the different memory pathways. 141 of the runners were tested within 30 min of finishing the race (when their cortex was still flush with cortisol) while the other 120 were tested 1-3 days before the race (this was the control group).

The end result? The group that had just finished the marathon showed a significant decline in explicit memory. They were less able to consciously recall a series of words that they had been shown only a few minutes earlier. However, after running 26.2 miles the marathoners actually showed a large improvement in implicit memory. In other words, the extreme stress and utter physical exhaustion sharpened their ability to act on information stored in their unconscious.

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In my experience the conscious mind's involvement totally messes up intuitive judgments so it would be interesting to know whether implicit memory improved because explicit was impaired or independently of it.

By just doug (not verified) on 30 Jul 2009 #permalink

As a marathon runner, I was really interested in this experiment. Perhaps I could add my 2 cents worth...

While running I feel like I can reach a meditative state a lot easier than any other form of meditation practice I've tried. This I only experience on the longer races (anything over a half marathon).
I think a study should be done on the relationship between someone who is able to meditate, or is in a meditative state for a long period of time and the results from this experiment, because I think they are related.

Meditation helps you to connect with your intuition and in layman's terms helps you to control the thoughts zooming around your head. Perhaps it is because of this meditative state that your explicit memory is improved.

As for the stress levels being on par with rape victims and first time parachuter s, all I have to say to that is that a marathon is a long way to force your body to run - there will be stress involved but depending on how well you are able to deal with it (perhaps this is where the meditative state comes into play) I guess depends on how your body reacts stress-wise.

Perhaps a similar effect happens when people are drunk. Explaining why a drunk can forget how many drinks they've had, but still strongly believe they can drive a car/balance walk along a wall/jump into the sea...a strengthening in the belief in things we can do alongside a loss of remembering the 'facts'..?

I'm probably not up on my memory research, but it seems as if you're equating implicit memory with motor memory.

What was the test of implicit memory that marathon runners were given?

It's highly possible to lose parts of what used to be called "semantic" memory - stored abstract knowledge - while retaining motor memory, and other parts of semantic memory. For an example where specialized systems are known to be involved, it's highly possible to have a brain lesion that more or less selectively destroys ability to write, and nothing else. Etc.

This post and the one yesterday about TV friends interest me especially in terms of how these situations reveal the inner workings of the brain. I think you got it exactly right when you described the brain as an attachment machine (TV friends) and when you mention the necessity to remember how to spear animals when being pursued by a hungry one. More and more the brain is turning out to be an evolutionary marvel. One recent study showed the brain keeps itself constantly busy to be at its peak when needed, thus we doodle when bored.

Sorry to be off topic, but...

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"the secret to being a great scientist is to love the manual labor of it."

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Would have been informative to test the runners explicit memory after 3 days. How quickly the body deals with the stress overload may mitigate significant effect. My guess is that extreme sports such as marathons are counterproductive to health and memory. In the short term it may seem we are improving health and stamina, but the release of free radicals will eventual cause an earlier decline.

Consistent, more moderate exercise punctuated by bouts of 100% effort (even in 90 second intervals, which is enough to aid diabetics in regulating glucose levels) would seem optimal. A recent study looking at injuries compared compulsive cyclists who trained in freezing conditions no matter and serious cyclists who, in the same conditions, trained indoors--the latter fair much better.

BTW: would like the list of Ph.D. programs LRA is applying for: precisely my interests.

is this why some people with high stress live hard burning the candle at both ends to a point of exhaustion to hold a sense of clarity?

As a marathon runner, I am very doubtful of the legitimacy of these tests. I am sure that a lot of people do not feel 100% fully capable of a lot of things after running a marathon. If this test were to prove anything, it should test the runners over a long period of time, before and after the race, days after, etc. Testing right after running 26 miles.... results might be a little skewed. But in any case, it would be interesting to see if there are any long term effects of running and the memory. In addition to that, they might have some variables in different groups of those that just run, those that do other things to stimulate the brain, etc. (which is what I hear helps prevent memory loss- things like crosswords and other brain challenges)

Although this study is facinating and worth looking into, the accuracy of the results is a bit questionable. Who is to say that runners are stressed while running. In fact, most runners (especially marathon runners) are trained and learn to get into their "zone" and almost meditative state in order not to get stressed or worn down. It is possible that the loss of explicit memory is not due to stress but perhaps when asked to repeat the list of words, they were still in their meditative state or were just coming out of their meditation. It can be assumed also, that after a 26 mile run, remembering a list of words is not on the runner's top priority list. As for the increase in implicit memory, this could be due to a runners practice of no being in a fully concious state when running. Being a runner myself, I have found that once I get into my mode, there is no stopping me and I am not fully concious of my body or the things going on around me. Therefore, this mode runners put themselves in could explain the increase of implicit memory.

Being a runner myself I found this study very interesting, but I would need a little more research to actually believe it. Although I only run cross country (5k races) which is no where close to a marathon I feel that the run actually does the opposite of what the study suggests. After a race I usually feel less stressed out from when I started, but perhaps running 26 miles instead of just 3 (or around 6 in practices) would be a completely different story.
I agree with jksB120's theory, that maybe the runners meditated state may have something to do with the results, but I think you also have to take into account the kind of marathon runners they interviewed. If the runners were running the marathon for personal achievement or if they were running it to get first place. If someone was in it to take first place perhaps they were stressed out just the same as someone who is losing at anything they really want, like a chess or basketball game for instance. Where as someone in the race for personal achievement would not stress over what place they were in, but be feeling a sense of relief that they are actually able to do it.

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