Increased neural responsiveness to distractors irrespective of perceptual load explains attention deficit in post-stroke fatigue.

Post-stroke fatigue (PSF) is a prevalent symptom associated with attention deficits. However, it is currently unclear what drives these. Here we applied Load Theory of Attention to investigate the role of perceptual load in the relationship between attention, distraction and fatigue levels in PSF. Thirty-two chronic stroke survivors performed a selective attention task of either low, medium or high perceptual load (varied through the number of relevant target features and their combinations). Neural responses to targets and distractor checkerboard flicker (vs. no flicker) were measured with frequency-tagged EEG responses. The results showed that fatigue severity scores were predictive of response slowing, and that this slowing was increased with higher levels of perceptual load. Fatigue severity was also associated with increased neural responsiveness to distractors, specifically: EEG 10 Hz (distractor flickering frequency) power was greater in the presence (vs. absence) of distractor flicker for participants with high (vs. low) fatigue-symptoms scores, across all levels of perceptual load in the later time period of each task trial. Overall, these results clarify the exacerbating effects of perceptual load on fatigue-related slowing, stressing the importance of cognitive, as opposed to purely motoric, deficits. Importantly, they demonstrate that increased fatigue severity involves reduced ability to suppress neural responses to irrelevant distractors, irrespective of perceptual load on attention. An account for attention in PSF based on a specific deficit in distractor suppression that is found irrespective of task demands can explain a myriad of PSF symptoms (e.g. sensory perceptual overload, difficulties to concentrate).