Study Suggests Cognitive Resilience in Idiopathic Hypersomnia

Adults living with idiopathic hypersomnia and narcolepsy type 1 often report cognitive difficulties, including problems with memory, attention, and mental fatigue. However, new research published in Sleep Medicine suggests that their overall intellectual abilities remain intact.

Although both narcolepsy type 1 and idiopathic hypersomnia are marked by excessive daytime sleepiness, idiopathic hypersomnia is more commonly associated with long, unrefreshing non-REM naps, prolonged nighttime sleep, and pronounced sleep inertia.² The disorder has no known cause, and clinicians diagnose it by ruling out other medical or sleep-related explanations for persistent sleepiness.

In this study assessing intelligence quotient in central hypersomnolence disorders, investigators administered the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV), to 29 adults with idiopathic hypersomnia, 30 with narcolepsy type 1, and 30 healthy controls.¹ Participants were closely matched for age, sex, handedness, and years of education. One participant with idiopathic hypersomnia was excluded from analysis due to extremely low educational attainment that could have biased results.

Full Scale WAIS-IV IQ scores differed across groups, with a mean score of 114.6 in the idiopathic hypersomnia group, 104.1 in the narcolepsy type 1 group, and 108.4 among controls. The overall group difference reached statistical significance with a medium effect size. However, neither patient group differed significantly from healthy controls in pairwise comparisons. Participants with idiopathic hypersomnia tended to outperform those with narcolepsy type 1.

Across specific cognitive domains, differences emerged in perceptual reasoning and working memory, again with idiopathic hypersomnia participants showing a tendency toward higher scores than those with narcolepsy type 1. The only individual subtest demonstrating a significant group effect was Visual Puzzles, a measure of visuospatial reasoning. On this task, the idiopathic hypersomnia group performed better than both narcolepsy type 1 participants and controls. No significant differences were observed on verbal comprehension or processing speed indices.

Importantly, IQ scores in both sleep disorder groups fell within the normal range. The proportion of participants with high intellectual potential, defined as an IQ above 130, was similar across groups, including 13.8 percent of those with idiopathic hypersomnia, 6.7 percent of those with narcolepsy type 1, and 10 percent of controls.

The study also examined factors associated with cognitive performance. Years of education correlated moderately with Full Scale IQ, General Ability Index, Verbal Comprehension Index, and Working Memory Index scores across the entire sample. In contrast, disease duration, age at onset, sleepiness severity as measured by the Epworth Sleepiness Scale, and treatment status were not associated with IQ performance.

Fatigue emerged as a more relevant factor than sleepiness. Higher pretest fatigue scores were associated with lower working memory performance, particularly among participants with narcolepsy type 1 and healthy controls. This association was not observed in the idiopathic hypersomnia group, raising the possibility that these individuals may rely on compensatory cognitive mechanisms to maintain performance despite fatigue.

During testing, which lasted 90 to 120 minutes, all participants completed the assessment without naps or breaks. However, clinicians noted greater fluctuations in attention among participants with narcolepsy type 1. Memory complaints were also more frequently reported in this group compared with controls, despite largely preserved objective performance.

The findings add to a limited body of research on intelligence in hypersomnolence disorders. While pediatric studies have documented normal IQ in children with narcolepsy type 1, intelligence had not previously been systematically assessed in adults with idiopathic hypersomnia. The present results suggest that global intellectual functioning remains preserved in adulthood for both conditions.

The authors note that IQ is a broad measure and may not capture subtle attentional or executive challenges reported by patients in daily life. Subjective cognitive complaints may reflect difficulty sustaining attention over time rather than deficits in core intellectual capacity. Neuroimaging research has pointed to possible structural and connectivity changes in idiopathic hypersomnia that could represent adaptive mechanisms supporting cognitive resilience, though further studies are needed.

Overall, the results challenge assumptions that chronic sleepiness necessarily translates into impaired intelligence. Adults with idiopathic hypersomnia and narcolepsy type 1 demonstrated normal general intellectual abilities, supporting their capacity for academic and professional achievement. At the same time, fatigue, attentional variability, and psychosocial stressors may still contribute to meaningful functional burden, underscoring the need for comprehensive clinical support.

References

1. Zhuang E, Dodet P, Leu-Semenescu S, et al. Intelligence quotient in adults with idiopathic hypersomnia and narcolepsy type 1. Sleep Med. Published online January 9, 2026. doi:10.1016/j.sleep.2026.108778
2. Arnulf I, Leu-Semenescu S, Dodet P. Precision Medicine for Idiopathic Hypersomnia. Sleep Med Clin. 2022;17(3):379-398. doi:10.1016/j.jsmc.2022.06.016