Impact of post stroke fatigue on saccadic eye movement control and learning through inflammatory mechanisms

This study aimed to (1) examine the impact of post-stroke fatigue (PSF) on saccadic control, (2) assess the effect of PSF on saccade adaptation, and (3) explore the correlation between serum levels of interleukin-6 (IL-6) and high-sensitivity C-reactive protein (hsCRP) with saccade control and adaptation in chronic stroke survivors. Fatigue was assessed in stroke survivors with high fatigue (HF-stroke, n = 13) and low fatigue (LF-stroke, n = 13) using the Fatigue Severity Scale and Fatigue Assessment Scale, alongside age-matched healthy controls (n = 13). The stroke groups were compared based on lesion volume and location. Eye-tracking recorded pro-saccade, anti-saccade, and saccade adaptation parameters. Serum levels of IL-6 and hsCRP were measured. HF-stroke survivors demonstrated significantly higher saccade latency, duration, and positional error, along with lower velocity, amplitude, and gain in pro- and anti-saccade tasks compared to the LF-stroke group (p < 0.05). HF-stroke survivors showed a lower adaptation rate (F_(2,36) = 144.38, p < 0.001, η² = 0.89) and adaptation after-effect (F_(2,36) = 98.93, p < 0.001, η² = 0.85) compared to other groups. The result revealed a significant main effect for group (F_{(2, 36)} = 1108.30, p < .001, η² = 0.98), BIN (F_{(9, 324)} = 318.05, p < .001, η² = 0.90), and group × BIN interaction (F_{(2, 324)} = 2.72, p = 0.01, η² = 0.13). Negative correlations were observed between serum levels of IL-6 and hsCRP and fatigue, saccadic velocity, adaptation rate and adaptation aftereffect in stroke survivors (p < 0.05). Both stroke groups showed significantly reduced gain in pro- and anti-saccade tasks compared to healthy controls, yet gain was not significantly correlated with IL-6 or hsCRP levels. The study demonstrated that fatigue significantly affects saccade control and adaptation in stroke survivors, with inflammation having a negative impact on these processes. Pro- and anti-saccadic gain was reduced in stroke participants but unrelated to inflammation, while adaptive gain during saccade adaptation correlated with inflammatory markers, suggesting a link between PSF, adaptation, and inflammation. These findings underscore the importance of careful assessment and management of fatigue in stroke survivors.