window around the scalp negative peak of the corresponding slow waves. The difference between corresponding computed phases was then obtained. Then, the phase locking across all slow waves was estimated for the time t and the frequency f by PLV ðt,f Þ~ ð1=N Þ P kN~1ejYk , where YK was the phase differ- ence (mod 2p) for the corresponding slow waves of index k and N the total number of slow waves. Supporting Information Figure S1 Histograms presenting the frequency distribution of detected gamma events associated with IN-phase (left) and ANTI- phase (right) patterns, for the examples presented in Figures 3A and 3B respectively. (TIF) Figure S2 Synchronization of gamma events as estimated through the cross-correlation coefficient (CC). (A) Histogram of the distance between pairs of contacts for all cases presenting co- detection probability $50% and statistically significant CC (n = 11 subjects). 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