A recent pilot study compared the effects of mental fatigue on brain activation patterns in people with and without multiple sclerosis. The findings suggest significant differences between the two groups in use of brain resources in response to increased mental activity. 

Mental fatigue comprises two types, state and trait, which are typically measured subjectively: state fatigue fluctuates over minutes to hours; trait fatigue is stable over longer periods, usually weeks. Focusing on state fatigue, the Kessler Foundation study included 36 participants: 19 with MS, and 17 controls. Participants underwent functional magnetic resonance imaging while performing the Symbol Digit Modalities Test, a standard cognitive test modified for use with fMRI. Changes in brain activity were recorded while the SDMT was given under two conditions: high and low cognitive loads.

The researchers found higher levels of fatigue and longer response times in the MS group. With increasing mental fatigue, the control group showed increased activation of regions at the front of the brain and faster speed of response, to meet the demands of the high mental activity. The MS group did not show activation of these regions or an increase in processing speed, suggesting a slower response to the higher mental demands of the task.

Results of the pilot study were consistent with prior research into the functional reorganization of brain activity in response to mental fatigue. 

The article was published in the Journal of Neurology.