Slow-Wave Sleep Spindle Density and Motor Sequence Learning Consolidation in Young and Older Adults: Polysomnographic and fMRI Evidence

This study investigates relationship between polysomnographically measured slow-wave sleep spindle density and overnight motor sequence learning consolidation in young versus older adults with fMRI striatal engagement as mediating mechanism within the context of sleep neuroscience and cognitive aging, an area of growing scientific importance given its implications for cognitive aging intervention, targeted sleep enhancement for motor rehabilitation, and sleep-based memory optimization in healthy aging. Using pre-registration of hypotheses; polysomnography with automated spindle detection (11-16 Hz, >0.5s duration), finger tapping sequence consolidation assessment, and fMRI striatal BOLD signal during next-day task performance, we examine NREM sleep spindles coordinating hippocampal-to-striatal memory replay, with spindle-SO coupling indexing efficiency of striatal motor skill consolidation, attenuated in aging by reduced spindle density and coupling fidelity in 96 participants: 48 young adults (mean 23.4 years) and 48 older adults (mean 68.4 years), all without sleep disorders (AHI <10, no medication affecting sleep) drawn from sleep laboratory polysomnography with EEG 64-channel recording and next-day 3T fMRI during motor task at Brookside University Hospital. Results indicate that spindle density predicts overnight motor consolidation across both age groups (r=0.58, p<0.001) with 38.4% lower spindle density in older adults driving 42.4% smaller consolidation gain; striatal BOLD mediates 44% of spindle-consolidation relationship (p < 0.001), with r=0.58 spindle-consolidation; 42.4% smaller gain in older adults; 44% striatal mediation as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to sleep neuroscience and cognitive aging and carry actionable implications for the design of programs and policies targeting cognitive aging intervention, targeted sleep enhancement for motor rehabilitation, and sleep-based memory optimization in healthy aging.