Highlights
- •Assessment of cognitive fatigue in early pwMS by adjusting for task demands.
- •pwMS do not show increased performance fatigability by comparison to controls.
- •pwMS report similar subjective fatigue level compared to controls.
- •Eye-metrics are sensitive to fatigue induction in early MS.
- •Pupil response speed seems a promising measure of cognitive fatigability in MS.
Abstract
Context
Cognitive fatigue (CF) is a disabling symptom frequently reported by patients with
Multiple Sclerosis (pwMS). Whether pwMS in the early disease stages present an increased
sensitivity to fatigue induction remains debated. Objective measures of CF have been
validated neither for clinical nor research purposes. This study aimed at (i) assessing
how fatigue induction by manipulation of cognitive load affects subjective fatigue
and behavioural performance in newly diagnosed pwMS and matched healthy controls (HC);
and (ii) exploring the relevance of eye metrics to describe CF in pwMS.
Methods
Nineteen pwMS with disease duration < 5 years and 19 matched HC participated to this
study. CF was induced with a dual-task in two separate sessions with varying cognitive
load (High and Low cognitive load conditions, HCL and LCL). Accuracy, reaction times
(RTs), subjective fatigue and sleepiness states were assessed. Bayesian Analyses of
Variance for repeated measures (rmANOVA) explored the effects of time, group and load
condition on the assessed variables. Eye metrics (number of long blinks, pupil size
and pupil response speed: PRS) were obtained during the CF task for a sub-sample (16
pwMS and 15 HC) and analysed with Generalized Linear Mixed Models (GLMM).
Results
Performance (accuracy and RTs) was lower in the HCL condition and accuracy decreased
over time (BFsincl > 100) while RTs did not significantly vary. Performance over task and conditions
followed the same pattern of evolution across groups (BFsincl < 0.08) suggesting that pwMS did not show increased alteration of performance during
fatigue induction. Regarding subjective state, both fatigue and sleepiness increased
following the task (BFsincl > 15), regardless of condition and group (BFsincl < 3). CF in pwMS seems to be associated with PRS, as PRS decreased during the task
amongst pwMS only and especially in the HCL condition (all p < .05). A significant Condition*Group interaction was observed regarding long blinks
(p < .0001) as well as an expected effect of cognitive load condition on pupil diameter
(p < .01).
Conclusion
These results suggest that newly diagnosed pwMS and HC behave similarly during fatigue
induction, in terms of both performance decrement and accrued fatigue sensation. Eye
metric data further reveal a susceptibility to CF in pwMS, which can be objectively
measured.
Keywords
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Article info
Publication history
Published online: June 26, 2022
Accepted:
June 24,
2022
Received in revised form:
June 10,
2022
Received:
May 20,
2022
Footnotes
☆AIM: To assess the effect of cognitive load on performance, subjective scales (fatigue and sleepiness) and eye metrics in early pwMS and HC.
Identification
Copyright
© 2022 Elsevier B.V. All rights reserved.
