I can’t be the only person who has started laughing out loud during a long run when a strange thought popped into my head, or who finds mental arithmetic simultaneously extremely important and almost impossible in the final few miles of a twenty miler. I call this my long run madness.
In my last article, I had a look at the beneficial effects of regular exercise on brain health, learning and memory. This time, I want to examine the effects of exercise on brain function while exercising.
What happens to the brain during exercise?
When a person goes from slumping in an office chair to running along a trail, a whole cascade of physiological adaptations are needed. The respiratory and cardiovascular systems make many of the adjustments that seem most apparent to the athlete: delivering oxygen to and washing waste away from the working muscles, which we experience as breathing faster and deeper and a racing heart, and maintaining a safe body temperature, hence the bright red face and sweat in your eyes.
In a truly elegant example of homeostasis (the scientific term for maintaining the body’s ideal steady state), even as blood flow to the working muscles increases, total blood flow to the brain is kept precisely the same whether relaxing or sprinting. In fact, the volume of blood reaching the brain with each heart beat is reduced by up to four times during exercise (because of all those other demands for blood supply), but this is perfectly counterbalanced by the increase in heart rate to keep your brain fuelled without “wasting” any more blood and oxygen there than strictly needed.
However, current thinking (pun intended) is that the brain has limited processing power; like a computer, if one program is using up a large proportion of available processing power, it has to be taken away from other processes. This means that although total blood flow to the brain remains constant, the available blood—and the oxygen and glucose it carries—is redirected to the most active areas of the brain.
During exercise, as you might expect, the key areas involved include the motor cortex and other areas controlling movement and the senses. As a result, blood flow is redirected to these areas in preference to others. In other words, to manage the strain of controlling all the processes involved in running, activity in any parts of the brain not integral to keeping you running are temporarily dampened down.
The main region affected in this way is thought to be the so-called prefrontal cortex, the part at the front of the frontal lobe (this is called the “hypofrontality theory”—see this 2003 paper[ii] for some of the evidence behind it, and a very interesting look at how this might be involved in the beneficial effects of exercise on mental health). The prefrontal lobes appear critical to working memory, task flexibility (switching from one line of thought to another), planning and predicting outcomes, choosing between good and bad options, and suppressing socially inappropriate actions.
There is a range of evidence supporting the idea that the prefrontal cortex is less active during exercise than at other times—studies measuring changes in regional glucose consumption in rat brains[iv], humans PET scans demonstrating changes in brain blood flow[v] and EEG (brain tracing) changes during exercise[vi] are consistent with the theory.
However, this doesn't necessarily tell us that there is a functional impact on the brain. In order to find out what these physiological effects actually mean, we have to look at experiments testing brain function during exercise.
How exercise affects cognitive performance
There have been many studies in which people took cognitive tests during or after exercise, but I’ll discuss an especially interesting paper from 2004[iii]. I say especially interesting because in the two experiments performed, the researchers explicitly tried to untangle any effects of exercise making people generally more alert, or conversely more tired, from the specific changes in brain activity described above.
In each experiment, they had 8 men running, 8 cycling, and 8 at rest (standing on a motionless treadmill or sitting on a stationary bike, in case there are mystical properties of standing on a treadmill or sitting on a bike that might affect test performance) for 50 minutes. All of the men had regularly engaged in at least 30 minutes of running or cycling at least 4 days per week in the previous 6 months. All of them had an introductory session in the laboratory so that they were at least minimally familiar with the environment, and they were asked not to exercise, eat or drink anything caffeinated on the day of the test. The lab was temperature-controlled and the work-rate was (unbeknownst to the participants) altered on the treadmills or bikes to maintain them in the range of 70-80% of their maximum heart rate.
In experiment 1, each participant took 2 tests after 25 minutes of either exercising or resting. One test was a general IQ test (verbal and non-verbal reasoning) and the other specifically tested prefrontal function—this involved sorting cards according to colour, shape or number, with the rule changing every time they got 10 right. The order in which they took the tests was random, in case this influenced how well participants did. They then compared the average results in IQ and prefrontal performance according to what participants were doing at the time.
In experiment 2, the participants again took 2 tests after 25 minutes, again a general IQ test and a prefrontal function test. This time, the researchers chose tests that people don’t generally get better at by practicing. The IQ section was a vocabulary test in which there are 2 different tests available, and the prefrontal test involved hearing a series of fifty numbers and having to add up each pair as it is said; again, there are 4 different series of numbers available, and tests show it doesn’t appear to get any easier with repetition. This time, they just tested the 8 runners, having them run for 65 minutes and rest for 65 minutes, taking both tests under both conditions.
In both experiments, they found no statistically significant difference in scores for the general IQ tests between exercise or rest, but significantly lower scores in the prefrontal tests for those excercising. This is good support for the hypofrontality theory—and argues against general alertness or general tiredness explaining the effects of exercise seen in other studies, since the IQ test scores remained the same.
What does this mean for runners? Well, I don’t think I have the perfect excuse for my long run madness yet, but there is certainly evidence of reduced function in the prefrontal area of the brain while the rest of the brain works on keeping us moving. Given the frontal lobe is involved in more complex things than those tested, such as suppressing socially inappropriate behaviour, maybe I at least have an excuse for the hysterical laughter.
I’ll try to breathlessly explain all this to the next bewildered pedestrian I run past at mile eighteen.
Dr Fenella Corrick
Ide, K. & Secher, N.H. Cerebral blood flow and metabolism during exercise. Progress in Neurobiology 61, 397-414 (2000).
[ii] Dietrich, A. Transient hypofrontality as a mechanism for the psychological effects of exercise. Psychiatry Research 145, 79-83 (2006).
[iii] Dietrich, A. & Sparling, P.B. Endurance exercise selectively impairs prefrontal-dependent cognition. Brain and Cognition 55, 516-524 (2004).
[iv] Vissing, J., Anderson, M., Diemer, N.H., 1996. Exercise-induced changes in local cerebral glucose utilization in the rat. Journal of Cerebral Blood Flow and Metabolism 16, 729–736.
[v] Fukuyama, H., Ouchi, Y., Matsuzaki, S., Nagahama, Y., Yamauchi, H., Ogawa, M., Kimura, J., Shibasaki, H., 1997. Brain functional activity during gait in normal subjects: a SPECT study. Neuroscience Letters 228, 183–186.
[vi] Nybo, L., Nielsen, B., 2001. Perceived exertion is associated with an altered brain activity during exercise with progressive hyperther- mia. Journal of Applied Physiology 91, 2017–2023.