Subjective cognitive fatigue in multiple sclerosis depends on task length.
OBJECTIVE
The objective of this paper is to investigate the interrelationship between subjective and objective cognitive fatigue, information processing domain [processing speed (PS) vs. working memory (WM)], cognitive load (high vs. low), and time on task in Multiple Sclerosis (MS).


METHODS
Thirty-two MS participants and 24 healthy controls completed experimental tasks in both the PS and WM domains with different levels of cognitive load. Subjective cognitive fatigue was measured using a visual analog scale at baseline and at multiple time points throughout the experiment.


RESULTS
A mixed model ANOVA revealed that subjective cognitive fatigue was higher for the PS task, increased across time, and was higher in the MS group. These findings were qualified by an interaction demonstrating that the MS group showed a steeper increase in subjective cognitive fatigue over time than the healthy control group. Subjective and objective (i.e., performance) cognitive fatigue were not correlated.


CONCLUSIONS
In this study, subjective and objective cognitive fatigue appears to be independent and cognitive fatigue does not depend on cognitive load. Subjective cognitive fatigue increased with time on task and subjective cognitive fatigue increased more steeply for the MS group. These data suggest that cognitive fatigue in MS is a function of time, that is, the longer participants were engaged in a cognitive task, the more likely it was for them to report increases in cognitive fatigue.
Neuropsychology and Neuroscience Research, Kessler Foundation , West Orange, NJ , USA ; Department of Physical Medicine and Rehabilitation, Rutgers - New Jersey Medical School , Newark, NJ , USA.
Joshua
J
Sandry
Neuropsychology and Neuroscience Research, Kessler Foundation , West Orange, NJ , USA ; Department of Physical Medicine and Rehabilitation, Rutgers - New Jersey Medical School , Newark, NJ , USA.
Helen M
HM
Genova
Neuropsychology and Neuroscience Research, Kessler Foundation , West Orange, NJ , USA ; Department of Physical Medicine and Rehabilitation, Rutgers - New Jersey Medical School , Newark, NJ , USA.
Ekaterina
E
Dobryakova
Neuropsychology and Neuroscience Research, Kessler Foundation , West Orange, NJ , USA ; Department of Physical Medicine and Rehabilitation, Rutgers - New Jersey Medical School , Newark, NJ , USA ; Department of Neurology and Neurosciences, Rutgers - New Jersey Medical School , Newark, NJ , USA.
John
J
DeLuca
Neuropsychology and Neuroscience Research, Kessler Foundation , West Orange, NJ , USA ; Department of Physical Medicine and Rehabilitation, Rutgers - New Jersey Medical School , Newark, NJ , USA ; War Related Illness and Injury Study Center, Department of Veterans Affairs , East Orange, NJ , USA.
Glenn
G
Wylie
cognitive fatigue; fatigability; processing speed; time; working memory