Calculation of the EEG alpha power time series (APTS) and intrinsic mode functions (IMFs).

<p>A: After removal of the MRI and ballistocardiogram artifacts, the EEG data from the four bipolar channels were subjected to frequency analysis using fast Fourier transform (FFT) for each 3-second segment (gray in the upper panel). The powers of the alpha band across the four bipolar channels were averaged. The averaged power values were then temporally aligned as the APTS, as shown in the bottom panel. A scalp topography of alpha power of a single subject is shown in the right middle panel. Note that the topography is described by EEG data of a unipolar induction, and L indicates the left side of the brain. B: An example of the IMFs for a single subject. An APTS of a single subject is shown in the upper panel. Next, the IMFs separated by the empirical mode decomposition (EMD) from the APTS were shown from the first to the fifth IMF.