Individualized Sigma-Frequency Targeting Improves Closed-Loop Auditory Enhancement of Sleep Spindles and Overnight Learning

Abstract

Sleep spindles (11–16 Hz) are markers of thalamocortical plasticity and predictors of memory consolidation, yet closed-loop auditory stimulation protocols often ignore inter-individual variability in spindle frequency. I tested whether tailoring stimulation to each person's sigma peak frequency improves physiological and behavioral outcomes relative to a conventional, fixed-band approach. In a preregistered, double-blind, counterbalanced crossover study (N=44; 18–32 y), participants completed two overnight sessions: (i) Personalized stimulation (bandpass and phase tracking centered on the individual sigma peak) and (ii) Fixed-band stimulation (canonical 12–15 Hz). Brief 50 ms pink-noise bursts (45 dB SPL) were delivered phase-locked to the late up-state of detected spindles during N2. Personalized targeting increased fast-spindle density at Cz by 13.8% versus Fixed-band and improved morning gains on a probabilistic sequence task by 9.6 ms (SE 3.5; p=.007) without altering sleep macro-architecture. Across nights, stimulation-induced changes in fast-spindle density predicted overnight improvement (β=0.27, p=.008) after controlling for baseline performance and total sleep time. Results indicate that respecting individual sigma dynamics enhances closed-loop efficacy and strengthens brain–behavior links central to consolidation.