FIG. 3.

Fourier spectrums of filtered and unfiltered phase-amplitude coupled signals. Fourier representations of phase-amplitude coupled sine waves at a carrier frequency of 40 Hz and amplitude modulations at 2, 6, and 10 Hz. The left column displays the frequency spectrum of the original signal. The central column shows the filter response of the fixed bandwidth filter (red) and the filtered signal (blue). The right column shows the filter response of the variable bandwidth filter (red) and the filtered signal (blue). The sidebands are preserved with the variable bandwidth filter at each modulation frequency. Color images available online at www.liebertpub.com/brain