Sex differences in sleep and memory relationships in older adults at risk for Alzheimer's disease.

Overnight memory retention did not differ between men and women overall.

• 80 participants completed overnight polysomnography with high-density EEG; 65 also completed the evening encoding/immediate recall and morning delayed recall word-pair task.
• Participants were cognitively unimpaired older adults enriched for Alzheimer's disease risk.

Exploratory analyses of proportional overnight retention suggested a sex × APOE ε4 interaction, with female ε4 carriers showing reduced overnight forgetting.

• Female ε4 carriers may show reduced overnight forgetting relative to female non-carriers and male carriers.
• The authors describe this as counterintuitive and exploratory.
• They suggest it may reflect compensatory or resilience-related sleep-memory mechanisms in cognitively unimpaired women at genetic risk rather than a protective effect of APOE ε4 itself.

Women had more N3 sleep and higher NREM delta and slow sigma power than men.

• Women spent more time in N3 sleep than men.
• Women had higher NREM delta power and slow sigma power than men.
• Based on overnight polysomnography with high-density EEG in 80 participants.

Sleep-memory associations differed by sex in the full sample.

• Greater N2 duration was more strongly associated with better overnight retention in men.
• Greater frontal slow sigma power and fronto-central fast sigma power were positively associated with retention in women.

In exploratory APOE-stratified analyses, sleep stage-memory relationships differed by sex among ε4 carriers.

• N2-memory associations were more positive in male than female APOE ε4 carriers.
• N3-memory associations were more positive in female than male carriers.
• Both differences remained significant after FDR correction.

TFCE-corrected topographic analyses found positive associations between NREM delta and sigma activity and overnight memory retention in female APOE ε4 carriers.

• Associations involved both delta and sigma activity.
• These were identified using threshold-free cluster enhancement (TFCE) correction.

The authors conclude that sex and APOE ε4 status may jointly shape neurophysiological pathways linking sleep and memory.

• Findings highlight sex-specific NREM sleep physiology and sleep-memory relationships in cognitively unimpaired older adults at risk for Alzheimer's.
• They emphasize considering sex as a biological variable in sleep, cognitive aging, and Alzheimer's research.