Sleep Spindles Briefly Shift Cortical Network Geometry in Two Independent Overnight EEG Datasets

Sleep spindles are short thalamocortical bursts during N2 sleep. This article asks whether they coincide with a brief change in the geometric structure of cortical EEG. Each 30 s window is summarized with a nine-coordinate Meta-Noetic Phase Space (MNPS) chart: mobility, deviation from an integration–segregation balance, and entropy/complexity. The primary test compared each spindle with its own pre-event baseline, weighting subjects equally, in three overnight recordings (ANPHY, N=27; BOAS, analysis N=110–112; RichSleep, N=24). In ANPHY and BOAS the balance-deviation coordinate rose at the spindle (+0.106 and +0.165; permutation FDR q=0.009 and 0.011). The same timing test in RichSleep was inconclusive (q=0.72; 160 paired events). A broader comparison with matched non-spindle N2 windows is baseline-sensitive and is not used as a substitute timing confirmation. Pre-spindle heart-rate and breathing state did not detectably change the size of this EEG-only effect under tonic composite anchors, including a dual-arm cardiorespiratory index in RichSleep, or under two lower-powered phase-resolved tests. This is a two-dataset timing result plus a scoped null, not a three-dataset mechanism confirmation.