Phase-amplitude coupling is most prominent during REM sleep. Phase-amplitude coupling is most prominent during REM sleep. A, Example of a continuous recording including epochs of waking and sleep. Periods of aWK and REM sleep are indicated by light green and blue horizontal traces. Gray bars on top show instantaneous animal speed; theta/delta power ratio (blue) and theta–HFO modulation index (black) are shown in the bottom plot. B, Comodulograms for aWK and REM epochs shown in A. C, Top, normalized peak power for LG (30–60 Hz), HG (60–100 Hz), and HFO (120–160 Hz) during aWK and REM. The normalization was obtained by subtracting the 1/f fit (see Materials and Methods and Scheffzük et al., 2011). Each data point corresponds to an electrode (LG, n = 30 electrodes across 7 rats; HG, n = 20; HFO, n = 36). CI95% for the paired difference between states was computed using the mean value over eligible electrodes for each rat (n = 7 animals; for Cohen’s d and p-values, see Table 1). Bottom, modulation index computed for theta phase and the amplitude of each frequency range. Notice larger theta–HG and theta–HFO coupling during REM sleep. D, Power spectral density (left) and mean theta power (right) during aWK and REM. Continuous thick lines represent median, and dashed thin lines 25th–75th percentiles. E, Phase-amplitude coupling strength as a function of theta amplitude for different fast oscillations during aWK and REM sleep. In these analyses, eligible electrodes were selected based on inspection of comodulograms; for LG, we used recordings from s. radiatum, s. pyramidale, and parietal cortex; for HG, from s. lacunosum-moleculare and s. pyramidale; for HFO, from stratum oriens-alveus and parietal cortex. Robson Scheffer-Teixeira, and Adriano B. L. Tort eNeuro 2017;4:ENEURO.0079-17.2017 ©2017 by Society for Neuroscience