Human Gamma Oscillations during Slow Wave Sleep Figure 3. Two patterns of phasic modulation of gamma oscillations by the slow waves. (A–B) Examples of IN-phase and the ANTI-phase modulation patterns of gamma oscillations recorded in intracranial contacts in the cingulate gyrus (subject P15) (A) and the superior temporal sulcus (subject P18) (B), respectively. From Top to Bottom: Superimposed scalp slow waves aligned around their central peak; Simultaneously recorded intracranial LFPs, also showing slow components; Intracranial filtered (30–120 Hz) signals with the average RMS activity (orange line); Average of their time-frequency representations. (C–D) Total number of gamma events, associated with IN-phase and ANTI-phase patterns respectively, detected along frequency (30–120 Hz) and time (2-seconds window around the scalp negative peak) for all patients (n = 19) and all analyzed contacts (n = 233). For IN-phase and ANTI-phase patterns, the cumulative histograms of their frequency distributions were illustrated (Top-Right and Top-Left) with the corresponding regression curves (red lines). Several dominant peaks were identified at fa<41, fb<67, fc<87, fd<105 Hz and f9a<70, f9b<97 Hz. The cumulative histograms of their first detection times (relatives to the intracranial central peak of the slow waves) are also illustrated (Bottom). doi:10.1371/journal.pone.0033477.g003 PLoS ONE | www.plosone.org 5 April 2012 | Volume 7 | Issue 4 | e33477