Although preliminary results for these three alpha factors revealed significant group differences (52), a comparison of corresponding factor loadings waveforms extracted separately for controls and patients indicated variability in the residual alpha factor loadings for patients that was eliminated by using these three factors as a spectral filter (Section S2 in the Supplement). This approach exploits the capacity of fPCA to isolate and remove overlapping broadband activity (cf. Figure S1 in the Supplement). A Varimax-fPCA of these data led to highly consistent alpha factors. As shown in Fig. 1A and B, these included low-alpha/theta (black lines, 9 Hz peak, 50% variance of filtered waveforms; waveform rise below 8 Hz) and high-alpha (red lines, 10.5 Hz, 34% variance) factors, with characteristic lateral and midline posterior maxima (respectively) for eyes-closed. The residual alpha factor (green lines, 11 Hz, 16% variance) will not be further considered, because it included a substantial low-beta contribution (12–20 Hz) and a maximum for eyes-open (i.e., a reversed condition effect), neither of which are characteristic of alpha activity.
