Objective Evidence of Post Exertional Malaise and Brain Fog in ME/CFS

Mar 01, 2018
exercise causes brain fog in ME/CF, mental and physical exertion cause brain fog in ME/CFS, Brain Fog can be measured .

Mental and Physical Exertion Cause Brain Fog

Cook et al. Neural consequences of post-exertional malaise in ME/CFS. Brain, Behavior and Immunity 62 (2017) 87-99.

This study was a collaboration between many well-known names in the ME/CFS field including Dr. Dane Cook in Wisconsin, Alan and Kathy Light in Salt Lake City and Gordon Broderick (formerly of Edmonton) in Florida with Nancy Klimas’s team.  The goal was to measure the impact on the brain of fatiguing and non-fatiguing physical and mental tasks using functional MRI as an objective measure.  Here are the tasks that were included:

  • Non-fatiguing mental task – recognizing numbers
  • Fatiguing mental task – paced auditory serial addition task (PASAT). This task is very hard.  It is often used in research of cognitive function in ME/CFS because most individuals with ME/CFS struggle with this skill.  The PASAT is one of the “games” in Brain HQ.  You are given two numbers say 3 and 4.  You add them and give the answer “7”.  Then you are given another number, say 8.  You add 8 to 4 and give the answer “12” and so on.  The numbers keep coming and one has to pay close attention to avoid getting hopelessly lost.
  • Non-fatiguing physical task – finger tapping
  • Fatiguing physical task – 30 minutes of exercise on a bicycle at 70% of predicted maximum heart rate. This exercise test has been used often in research and is considered less exhausting than Stephen’s protocol which exercises participants “to exhaustion”.

No significant differences were found between the participants with ME/CFS and the healthy individuals (the same age, gender and activity level) during or after the non-fatiguing tasks.

A big difference between groups was found on the PASAT cognitive test both before and after the exercise task. The healthy individuals used fewer brain areas after exercise whereas the ME/CFS group activated more brain regions to complete the PASAT after exercise.  Despite using more brain resources, the ME/CFS group had poorer scores on the PASAT within the task (as they tired during the task) and post-exercise.  The changes in brain function correlated with the participants’ subjective reports of post-exertional malaise.  In other words, the participants with ME/CFS correctly judged that their brains were tiring.

The authors conclude that these findings provide objective support for the subjective experience of “brain fog” reported by ME/CFS patients when they attempt to be physically or cognitively active.  This study supports the use of challenge tests rather than a resting state to more clearly see the differences between people with ME/CFS and healthy individuals.

 Author: Eleanor (Ellie) Stein MD FRCP(C)

I am a psychiatrist with a small private practice in Calgary and am an assistant clinical professor in the faculty of medicine at the University of Calgary. Since 2000, I have worked with over 1000 patients, all with ME/CFS, FM and ES. My passion for this field comes from my own struggle with these diseases, my desire to improve my health and then pass on what I learn. My goal is for every patient in Canada to have access to respectful, effective health care within the publicly funded system. If you are looking for help and resources to help combat ME/CFS, FM and ES, see my guides and webinars.


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