Sleep inertia, the groggy, impaired state upon waking, is uniquely associated with deficits in fine motor speed and executive function in older adults, even after accounting for overall daytime sleepiness and other hypersomnolence symptoms, according to a study from the Wisconsin Sleep Cohort published July 6 in the Journal of Clinical Sleep Medicine.
The association was specific: neither daytime sleepiness (measured by the Epworth Sleepiness Scale) nor general hypersomnolence severity showed any relationship with cognitive performance. Only sleep inertia, assessed by the validated Sleep Inertia Questionnaire, predicted cognitive outcomes.
What they found
The study analyzed 461 community-dwelling older adults (mean age 73.8 years, 55.8% male) from the Wisconsin Sleep Cohort. Participants completed the Sleep Inertia Questionnaire (SIQ), the Epworth Sleepiness Scale (ESS), the Hypersomnia Severity Index (HSI), and a battery of six cognitive tests.
In unadjusted analyses, SIQ total score was significantly associated with performance on three tests, Grooved Pegboard (fine motor speed and dexterity), Trail Making Test-Part B (executive function and set-shifting), and Symbol Digits Modalities Test (processing speed). Neither the ESS nor the HSI showed any association with cognitive outcomes.
After full adjustment for demographic, psychosocial, sleep, and testing covariates, the associations between SIQ and both Grooved Pegboard and Trail Making Test-B remained significant. Processing speed (Symbol Digits Modalities) did not survive adjustment.
SIQ subscale analysis revealed that the physiological, cognitive, and emotional components of sleep inertia were each independently associated with cognitive tests, particularly Grooved Pegboard and Trail Making Test-B.
Why it matters
Sleep inertia is widely experienced but remains understudied, particularly in aging populations where cognitive decline is a growing concern. The finding that sleep inertia, not general sleepiness, is the hypersomnolence symptom that matters for cognition suggests it may represent a distinct neurobiological phenomenon rather than a mere proxy for poor sleep.
For clinicians, this means that asking about morning grogginess may be more revealing than standard sleepiness scales when evaluating an older patient’s cognitive complaints. For researchers, the SIQ emerges as a tool that captures a dimension of hypersomnolence that the ESS and HSI miss entirely.
Limits
The study is cross-sectional, so directionality cannot be established, sleep inertia could cause cognitive deficits, cognitive decline could worsen sleep inertia, or a shared mechanism could drive both. The cohort is predominantly non-Hispanic white, limiting generalizability. The cognitive battery, while well-validated, did not cover all domains of cognition.
Bottom line
Sleep inertia severity in older adults is specifically linked to deficits in fine motor coordination and executive function, independent of how sleepy a person feels during the day. The Sleep Inertia Questionnaire may be a valuable addition to cognitive risk assessment in geriatric and sleep medicine.
Source
Love JJ, Cook JD, Hagen EW, et al. “Association between sleep inertia and cognitive performance among older adults in the Wisconsin Sleep Cohort study.” Journal of Clinical Sleep Medicine. 2026 Jul 6;22(1):105. DOI: 10.1007/s44470-026-00133-4