The role of fatigue in attentional processing in multiple sclerosis: data from event-related potentials

Fatigue is an extremely common symptom in in people with multiple sclerosis (PwMS) and has a severe impact on quality of life. The purpose of the present study was to verify whether fatigue in PwMS is associated with a selective covert attention impairment, as measured by event-related potentials and to assess whether it is more associated with an impairment of top-down or bottom-up attentional control. Twenty-two PwMS and fatigue-MSF, 17 without fatigue-MSnF and 35 healthy volunteers underwent a three-stimulus P300 novelty task that elicits both the P3a and the P3b components. P3b latency was comparable between groups, but PwMS, independently from the presence of fatigue displayed significantly greater P3b amplitudes. P3a latency was significantly prolonged in MSF alone, while P3a amplitude in MSnF group was greater than controls. MSF were able to categorize the task-relevant target stimulus but the orienting response to a novel salient stimulus was delayed, indicating an impairment in bottom-up attentional control mechanism related to ventral attention network. Fatigue is selectively associated with a covert attentional deficit related to the ability to reallocate attentional resources to salient stimuli, a crucial function of adaptive decision-making behaviour.