EEG Microstate Clustering to Evaluate Acoustic Stimulation Phase-Locked Targeting of Slow Wave Sleep Activity

Closed-loop acoustic stimulation is a promising method for enhancing properties and quality of deep sleep. Additional synchronization of slow waves seems to be the result of auditory stimulation. However, the temporal parameters of typical deep sleep slow waves may be altered. We investigated this hypothesis by performing EEG microstate (MS) analysis. Further, we evaluated benefits of analysis for determining the precision of phase-locked stimulation precision. We obtained 4 MS template maps from non-rapid eye movement 3 (NREM 3) intervals of sham group’s sleep. By backfitting these templates to short data segments following stimulation or sham markers we have shown an overall dominance of frontally oriented microstate spatially related to canonical MS D in the stimulation group, which was not observed in sham group. This MS map can be linked with frontal neuron synchronization typical for low-frequency characteristic of deep sleep. Larger occurrences of this MS map may illustrate the process of sleep deepening during the stimulation. Comparing global field power (GFP) curves for stimulated subjects with polar histograms of precision we observed a relation between targeting precision for specific phases of stimulation with uniformity of MS distribution. Subjects stimulated more precisely had more uniform MS distribution in GFP’s, mostly dominated by MS 2. If confirmed by subsequent studies this property could serve as a marker of stimulation algorithm’s precision.