The bandwidth of the filter used to obtain fp and fa is a crucial parameter in calculating PAC (Aru et al., 2015). The filters for extracting fa need to be wide enough to capture the center frequency ± the modulating fp. So, for example, to detect PAC between fp = 13 Hz and fa = 60 Hz, requires a fa bandwidth of at least 13 Hz [47 73]. If this condition is not met, then PAC cannot be detected even if present (Dvorak and Fenton, 2014). We therefore decided to use a variable bandwidth, defined as ±0.4 times the center frequency (e.g., for an amplitude of 60 Hz, the bandwidth was 24 Hz either side [36 84]), which has been shown to improve the ability to detect PAC (Berman et al., 2012; Voloh et al., 2015). For alpha-band phase (maximum 13 Hz), this allowed us to calculate PAC for amplitudes above 34 Hz. The bandwidth for fp was kept narrow (1 Hz ± the center frequency), in order to extract sinusoidal waveforms. Furthermore, each trial was visually inspected to confirm that the fp filtered oscillations were sinusoidal in nature.
