Temporal and topographic effects of longer auditory stimuli on slow oscillations during slow wave sleep

Closed-loop targeted memory reactivation (CL-TMR) is a novel method for precise targeting and reactivation of selective memories consolidated during sleep. Electrophysiologically, slow oscillations (SOs) are evoked, associated with increased depth of non-rapid eye movement (NREM) 3 sleep. We performed evoked response potential (ERP) analyses on NREM 3 sleep data collected during auditory stimulation with 300 ms sounds. SOs were further characterized using topographical mapping and Hjorth parameters, with trials categorized into upstate and downstate segments based on stimulation phase. Our findings revealed significant differences between spontaneous and evoked SOs in both topographical distribution and signal complexity. Upstate stimulations produced stronger responses in frontal and occipital regions, particularly around the P300 component, suggesting greater cognitive processing than downstate stimulation, confirmed by a subsequent spectral entropy analysis. Finally, time–frequency analyses of post-stimulation EEG, using image-based feature extraction, revealed no distinctions between effects of individual cues. Despite variability in acoustic properties, the evoked SOs remained spectrally similar, indicating similar early processing brain responses across different stimuli and suggesting that using a higher stimuli number may not be optimal for CL-TMR experiments.