The debilitating mental fatigue that people with multiple sclerosis (MS) can feel after a cognitively demanding task may be due to less efficient use of the brain, a pilot study that mapped brain activity during tasks suggests.
The study “Neural mechanisms underlying state mental fatigue in multiple sclerosis: a pilot study” was published in the Journal of Neurology.
Mental and physical fatigue is a prevalent MS symptom, affecting 53 to 90% of patients, and known to affect daily life, work, social interactions, and mood. In research, it is considered to come in two forms: ‘state fatigue,’ a temporary fatigue that fluctuates over minutes or hours; and ‘trait fatigue,’ which holds stable for longer periods (weeks) and it is related with cognitive and sleep issues.
No gold standard for treating fatigue currently exists. Some non-pharmaceutical approaches have shown promise, but high quality clinical trials to validate their effectiveness are lacking. Hence, there is an urgent need to explore, and better understand, the mechanisms behind fatigue in MS.
A team led by researchers at the Kessler Foundation investigated how mental, or cognitive, fatigue affects brain function in MS patients, with a focus on ‘state fatigue.’
Mental fatigue is used to describe the mental exhaustion experienced after completing a task that demands higher thinking.
They used functional MRI (fMRI), a type of neuroimaging that allows researchers to detect which areas of the brain are active, and a cognitive task called Symbol Digit Modalities Test (SDMT). SDMT is a commonly used tool in MS research that consists in a substitution task of symbols and numbers to assess memory and processing speed.
Two SDMT test conditions were given: one with high cognitive load that requires rapid information processing of many symbols, and another of low cognitive load. Participants performed four runs of the one condition before doing four runs of the other.
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