Researchers have recently tested the idea that in highly strenuous exercise, such as marathon running, extreme physical demands are placed on an athlete that may result in neurohormonal changes, which alters the functioning of their memory.

Exercise is known to have an influence on neuromodulators that affect memory. Moderate levels of aerobic exercise, which would not be considered stressful, have emotional, cognitive and physiological effects. These include beneficial effects on mood, cognitive speed, hearing and visual attention. But researchers from Columbia University, New York wanted to look at the effects of heavy, strenuous exercise.

Research into physiological effects of marathon running has highlighted negative consequences, including dehydration, muscle damage and immune suppression. Marathon running also increases production of cortisol and norepinephrine, hormones that are elevated by physiological and emotional stress. Leading experts have concluded that ‘marathon running is one of the most stressful activities in which normal, neurologically intact humans engage’.

In this month’s Psychonomic Bulletin and Review journal, researchers studied the effects of marathon running on implicit and explicit memory tasks. Explicit memory is the conscious recollection of memories. Explicit memories are obtained by questions such as ‘what happened an hour ago?’, or ‘what were the items on the list you just read?’. Implicit memory allows you to perform a task without consciously thinking about the activity such as tying a shoe lace or a test could involve being given a word stem (first few letters of a word) and being asked to complete it.

The study involved testing 120 marathon runners during the expo’s for the New York City and Boston marathons as the control group, and testing 141 runners within 30mins of completing either marathon. The researchers used a test similar to one used to test implicit and explicit memory in amnesiac patients.

Thirty nine words of 4-7 letters in length were selected and 26 were randomly chosen on the first page for the subjects to rate for pleasantness. The second page had 3 letter word stems and the subjects had to make each stem into the first English word that came to mind. The third page had 13 word stems from page one and 13 word stems previously unrated as a baseline. The subjects had to try to complete the cue with words seen on page one.

The researchers found that runners tested immediately upon completing the marathon showed impairment in the explicit (cued recall) memory task, however, on the implicit (word stem completion) task the marathon group performed better than control.

The findings in the paper by Teal Eich and Janet Metcalfe, show that human memory functioning can be dynamically altered by strenuous activities such as marathon running, an activity in which hundreds of thousands of healthy normal individuals routinely participate in. The researchers conclude that the post-marathon impairment in explicit memory is similar to that seen with amnesiac patients with organic brain damage. These findings show for the first time that following completion of a marathon there is also a simultaneous enhancement in implicit, automatic memory.

So there is your proof. If you want to improve your unconscious memory, get out and run a marathon!!