Abstract :
[en] Introduction. Trait cognitive fatigue (tCF) is a persistent and aversive feeling of reduced mental efficiency, lasting from weeks to months. Fatigue is highly prevalent (>50%) in many neurological conditions (e.g., MS, Parkinson’s, stroke, cancer). Among people living with AD (PL-AD), tCF remains under-investigated. Only indirect evidence links fatigue in at-risk or early AD to brain atrophy, β-amyloid/Tau burden, and cognitive decline. Disruption of sleep-wake rhythms, which are known to impair cognitive functioning, may contribute to tCF in AD. Understanding this link could help clarify the mechanisms influencing cognitive fatigue in PL-AD and guide strategies to better support daily life and wellbeing.
Method. Nineteen individuals with mild-to-moderate AD (mean age = 76.8 ± 6.4 years; 26.3% females; education = 14.4 ± 2.9 years; MoCA = 20.1 ± 2.64) and nineteen healthy controls (mean age = 76.9 ± 7.0 years; 26.3% females; education = 13.4 ± 2.8 years; MoCA = 26.5 ± 1.71) completed two trait fatigue questionnaires (FSMC, BFS). Cognitive and physical fatigue composite scores were derived from PCA. Actigraphy over seven days yielded metrics of circadian rhythm amplitude (RA), behavioral fragmentation (kRA, kAR), and sleep-wake regularity (SRI, IS), as well as nap indices. Group differences were tested using linear regression adjusted for age, sex, and education (p < .05). Associations between fatigue, cognition, and actigraphy were examined using Spearman’s correlations.
Results. Composite scores showed good psychometric properties (explained variance >77%). Compared to controls, people with AD exhibited higher levels of cognitive fatigue (β = 0.613, p = .036, η²p = .127), but not physical fatigue (β = 0.467, p = .114). Actigraphy revealed significantly greater behavioral fragmentation in AD, both for rest-to-activity (kRA: β = 0.103, p = .042, η²p = .119) and activity-to-rest transitions (kAR: β = 0.066, p = .008, η²p = .194), along with lower sleep regularity (SRI: β = −11.94, p = .021, η²p = .152). No group differences emerged for sleep midpoint, total sleep time, or napping indices. Within the AD group, cognitive fatigue was positively associated with kAR (ρ = .464, p = .045) and negatively with SRI (ρ = −.468, p = .045). Moreover, MoCA scores correlated positively with cognitive (ρ = .480, p = .037) and global fatigue (ρ = .476, p = .039), as well as with sleep regularity (ρ = .635, p = .003).
Conclusion. Trait cognitive fatigue (tCF) in AD may represent an early, disease-specific symptom. Findings point to more fragmented activity patterns and reduced circadian regularity in AD, consistent with actigraphy studies in dementia. Circadian and sleep-wake disruption are likely contributors to persistent fatigue and cognitive decline in AD. Importantly, activity fragmentation was linked to higher tCF in AD, suggesting that fragmentation may contribute to cognitive vulnerability.
