fMRIs Show Mental Fatigue’s Impact on MS Patients’ Cognitive Cerebral Responses

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Fatigue & weakness
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Scientists at the Kessler Foundation and collaborators conducted a pilot study comparing the effects of mental fatigue on brain activation patterns in people with and without multiple sclerosis (MS). Their findings indicate significant differences between the two groups in their recruitment of neural resources in response to increased task demands.

The team views its study as a critical first step in the development of interventions to counter mental fatigue among MS patients.  The research “Neural mechanisms underlying state mental fatigue in multiple sclerosis: A pilot study” appears in the Journal of Neurology.

“Neuroimaging underpinnings of state (in the moment, transient) mental fatigue in multiple sclerosis (MS) are not well understood. The current pilot study examined the effect of state mental fatigue on brain activation (measured using functional magnetic resonance imaging [fMRI]) during conditions of varying cognitive loads of rapid information processing in persons with MS relative to healthy controls. Nineteen persons with MS and 17 healthy controls underwent fMRI scanning while performing a modified version of the Symbol Digit Modalities Test, which consisted of high and low cognitive load conditions with comparable visual stimulation. State mental fatigue was assessed using the Visual Analog Scale of Fatigue before and after each run of the behavioral task,” write the investigators.

“Results indicated that the healthy control group recruited significantly more anterior brain regions (superior and middle frontal gyri, insula, and superior temporal gyrus) to meet increased task demands during the high cognitive load condition as fatigue level increased (p < 0.05), which was accompanied by shorter response time. In contrast, the MS group did not recruit anterior areas to the same extent as the healthy control group as task demands and fatigue increased. Indeed, the MS group continued to activate more posterior brain regions (precuneus, lingual gyrus, and middle occipital gyrus) for the high cognitive load condition (p < 0.05) with no improvement in speed. In conclusion, persons with MS may allocate neural resources less efficiently than healthy controls when faced with increased task demands, which may result in increased mental fatigue. Results of the current pilot investigation warrant replication with a larger sample size.”

The study extended the Foundation’s investigation into the neural correlates of mental fatigue in MS. Mental fatigue comprises two types, state and trait, which are typically measured subjectively. The current study focused on state fatigue, which fluctuates over minutes to hours; trait fatigue is stable over longer periods, usually weeks.

“We found higher levels of fatigue and longer response times in the MS group,” said Michelle H. Chen, PhD, postdoctoral fellow in the Center for Neuropsychology and Neuroscience Research at Kessler Foundation. “With increasing mental fatigue, the control group showed increased activation of the anterior brain regions and faster speed of response, to meet the demands of the high load condition. The MS group did not show activation of these regions or an increase in processing speed, suggesting a less efficient response to the higher cognitive 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, according to Helen Genova, PhD, assistant director of the Center for Neuropsychology and Neuroscience Research. “In the absence of effective treatment for the disabling fatigue that affects many individuals with MS, it is essential to expand our understanding of these underlying brain mechanisms.”

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