Frequency spectral analysis
Frequency spectral analysis was performed using a fast Fourier transform (1000-point) algorithm. The absolute power spectral density (PSD, dB, 10log10(V2/Hz)) for each channel was calculated based on the periodogram. Relative PSD (rPSD) was computed by normalizing the total power over the entire frequency range. The absolute and relative PSDs were averaged across channels within groups to measure the global comparisons between groups in each frequency band. A group comparison of the PSDs for each channel was also performed.