Monday, July 13, 2009

I Just Finished the Boston Marathon! (but I can't remember your name)

Third place finisher Ryan Hall at the 2009 Boston Marathon.
Photo courtesy of
Martin Checkoway.

Running a 26.2 mile marathon is an exhausting endeavor for anyone, from the top Ethiopian and Kenyan runners to the astounding 75 year old Jim Schleisman (who finished in 3:45:33) to the back of the pack casual joggers runners. Two psychologists from Columbia university reckoned that the physical stress of marathon running might result in cognitive impairments (Eich & Metcalfe, 2009). Although the benefits of moderate aerobic exercise are well-documented, levels of cortisol [a "stress hormone" produced by the adrenal glands] after strenuous marathon running are four times greater than those observed after laboratory-based stress induction paradigms.
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).
Thus, along with parachute jumping, marathon running presents an ethical opportunity for studying the effects of extreme cortisol levels on cognitive processing. In particular, cortisol may disrupt hippocampal function and explicit memory -- the conscious recollection of previously learned information (Brunner et al., 2008). In contrast, implicit memory is thought to be unconscious and independent of the hippocampus, as demonstrated in studies of amnesic patients where impairments in explicit memory are accompanied by intact implicit memory performance (Squire, 2004).1

So would completing a marathon differentially affect explicit and implicit memory? The authors predicted the following:
Our hypothesis was that when marathon runners had just undergone the stress of running a marathon as compared with several days earlier, their performance on the explicit cued recall task would be impaired. At the same time, we predicted that their performance on the implicit stem-completion task would be spared or might even be enhanced.
The participants were 261 individuals who had completed either the New York City Marathon or the Boston Marathon: 141 were tested within 30 min of finishing, while the other 120 were tested 1-3 days before the race. All participants were given an implicit memory test (word stem completion) and an explicit memory test (word stem cued recall). Both tasks involve studying a list of words, followed by a series of 3-letter word stems. The instructions dictated which form of memory was to be evaluated, as described in the Procedure:
Participants rated 26 words for pleasantness on a 5-point scale. Text on the second page informed participants that each of the cues on the subsequent page would be the beginning of an English word. Their task would be to write a few letters to make each cue into any English word, but they were instructed to write down the first one that came to mind. The next page, which presented the implicit word-stem completion task, contained word stems from 13 words that were previously rated for pleasantness as well as stems from 13 unrated (baseline) words, randomly intermixed. Following completion of the implicit memory task, participants were given instructions for the explicit memory cued recall task. They were told that each of the cues on the subsequent page was the beginning of a word for which they had provided a pleasantness rating earlier. They were instructed to try to complete each cue with the word from the pleasantness-rating list—that is, to explicitly remember the previously rated words. They were also instructed not to look back at the list. After reading these instructions, they turned to the last page, which contained the 13 remaining three-letter word stems presented in a random order, all of which they had previously rated for pleasantness. Given the cues, they then attempted to recall the words.
The brief example below gives a list of words seen during the study phase, followed by a series of word stems that are either completed with the first word that comes to mind (implicit memory), or used as cues to recall words from the study phase (explicit memory).




The results below illustrate that a dissociation between the two forms of memory was observed.

Figure 1 (Eich & Metcalfe, 2009). Performance on the implicit and explicit memory tasks. The left bars give the difference between the control (premarathon) and marathon (postmarathon) groups on the implicit memory word-stem completion task. The right bars give control group and marathon group performance on the explicit cued recall task. Priming is the difference in the proportions of correctly completed presented and unpresented (baseline) words.

As predicted, there was a significant decline in explicit memory after running a marathon. Less expected (but still not a complete surprise) was an increase in performance on the implicit memory task. The authors
interpret the results as suggesting that complex neuromodulation associated with extreme stress enhances some brain systems and inhibits others... As we acknowledged in our introduction, marathon running results in a host of other physiological changes [beyond increased cortisol], some of which may lead to decrements in explicit memory. However, consideration of those factors alone provides no obvious explanation as to why marathon running led to improved implicit memory.
Nevertheless, do they have a tentative conclusion about why that happened?
...Stress hormones, including norepinephrine, endorphins, and others, are surging in marathon runners. It is not unreasonable to suppose that these hormones serve to improve certain kinds of mental function.
But don't even try to remember where you parked your car...


1 But see Berry et al., 2008 for the opposing view that explicit and implicit memory are not independent and dissociable forms of memory.


Berry CJ, Shanks DR, Henson RN. (2008). A unitary signal-detection model of implicit and explicit memory. Trends Cog Sci. 12:367-73.

Brunner R, Schaefer D, Hess K, Parzer P, Resch F, Schwab S. (2006). Effect of high-dose cortisol on memory functions. Ann N Y Acad Sci. 1071:434-7.

Eich, T., & Metcalfe, J. (2009). Effects of the stress of marathon running on implicit and explicit memory Psychonomic Bulletin & Review, 16 (3), 475-479 DOI: 10.3758/PBR.16.3.475

Squire LR. (2004). Memory systems of the brain: a brief history and current perspective. Neurobiol Learn Mem. 82:171-7.

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At July 13, 2009 6:47 AM, Anonymous Anonymous said...

Whoa whoa whoa... before you go any further, NO ONE who runs a marathon is a "back of the pack casual jogger." There is nothing casual about training for 26.2 miles, and frankly, it's a little insulting to use that phrase for anyone who manages to finish one... even for those whom it takes five, six, or seven hours.


At July 13, 2009 11:33 AM, Blogger The Neurocritic said...

Sorry I offended you, Anonymous, but such things do happen:

In his marathon debut, Hideki Okajima may have been slow on the delivery (6 hours 35 minutes) but he accomplished his goal.

"I didn't put my 100 percent into it this time," said Okajima, wiping his brow. "I just had to watch my running and pace myself. Sometimes I took a rest and sometimes I was walking."

At July 13, 2009 11:58 AM, Blogger The Neurocritic said...

Here are the results for the 2008 Honolulu Marathon, which is known for letting everyone finish by not closing down the course after 6-7 hours.

At July 13, 2009 7:21 PM, Anonymous C said...

Is there any controlling for blood sugar levels? That seems like a major confound to me. Cortisol would seem to be only one piece of the puzzle in all this.

At July 15, 2009 10:57 AM, Blogger Neuroskeptic said...

Memory researchers seem to like "extreme" experiments. The main thing I remember from my Psych 101 course was that experiment where they tested memory for information learned while underwater.

On another note, maybe if Rosie Ruiz had known about this phenomenon she would have had an excuse for why she appeared out of nowhere - "I don't remember how I won the race. Blame my hippocampus".

At July 16, 2009 11:17 AM, Anonymous Mimi Fleischman said...

The stress of intense exercise affects our brains as well as our bodies. Studies show that lactic acid stimulates your endocrine system to produce our bodies' own natural anti-aging serum, human growth hormone. So intense exercise makes you younger as well as deeper (understanding implicit cues)!

At July 16, 2009 2:11 PM, Blogger The Neurocritic said...

Mimi - what specific studies are you talking about? Here's a paper showing huge differences in GH production in young (18-25) and middle aged (40-50) men during sprint and endurance exercise (Gilbert et al. 2008).

Neuroskeptic - that was a classic hoax:

Rosie Ruiz slipped out of Boston yesterday, slightly shaken by all the furor stirred up by her alleged victory in the 84th Boston Marathon and maintaining to the end in a series of interviews that, "I ran the race. I cannot stand there and say, 'I did not.' "

I wondered whether there might be some sort of delusional thinking but discovered she was a cocaine dealer instead (nice that she's pictured next to Indira Gandhi in that article!).

C - I agree that glucose levels were a confound, one that was outside of the experimenter's control.

At July 30, 2009 9:49 AM, Anonymous Kyle said...

Did they control for training, finish time, previous marathon experience, etc? Did the research article discuss any differences between participants in the New York City Marathon vs. the Boston Marathon? Since the majority of runners in the Boston Marathon have to hit a certain time in a prior marathon to qualify for the race, I'd imagine they might be different than the folks in the New York City Marathon (open to anyone).

Of course, I guess you could argue it either way: 1.)The Boston Marathoners should be less stressed because they have more training or 2.)The Boston Marathoners are more stressed because they are running faster.

At July 31, 2009 12:10 AM, Blogger The Neurocritic said...

Kyle - They did analyze Boston and New York participants separately, and got the same result in each case. There was no effect of running time on implicit memory, but faster runners did a little better on the explicit task:

"Control group participants averaged slower running times than did marathon group participants. We therefore performed two ANCOVAs, the first with implicit score as the dependent variable, group as the fixed factor, and running time as the covariate. There was no effect of running time on implicit memory... We performed the analogous ANCOVA with the explicit scores. Running time, here, had a significant effect... The effect of group, controlled for running time, was slightly stronger than before, indicating that the difference in running times across groups had been partially masking the negative effects of marathon running on the explicit memory task."

At August 03, 2009 1:08 PM, Anonymous Anonymous said...

So does this study mean that there is a correlation between marathon runners and poor memory? I know that scientists determined through rat studies that cortisol can kill you, but scientists are not sure how much it takes to kill you.


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