Is sleep-dependent memory consolidation reduced in mild cognitive impairment?

Details

The study investigated whether sleep-dependent memory consolidation (SDMC) is reduced in people with mild cognitive impairment (MCI), who are at high risk of progressing to dementia, compared with cognitively healthy controls. It also examined whether SDMC is associated with sleep characteristics, daytime episodic memory, and hippocampal integrity.

Participants with MCI (n = 43) and controls (n = 20) underwent clinical and neuropsychological profiling. Polysomnography was used to derive the apnea-hypopnea index (AHI) and non-REM sleep spindle characteristics. Magnetic resonance imaging was used to calculate hippocampal subfield volumes. Before sleep, participants learned a new set of 32 word pairs, and their retention of the pairs in the morning was used to determine SDMC.

SDMC did not differ between the MCI and control groups overall, but those with multiple-domain MCI showed a decrement in SDMC with a large effect size (Hedge's g = 0.85). In the MCI group, poorer SDMC was correlated with atrophy in the CA1 and CA3 hippocampal regions, shorter spindle duration, and worse daytime episodic memory. In controls, poorer SDMC was associated with a higher AHI.

The authors identified impaired daytime memory consolidation, reduced hippocampal volumes, shorter sleep spindles, and greater sleep apnea severity as indicators of diminished SDMC in older adults that should be explored in future studies.