working memory paradigm, which requires identifying the correct position of a probe letter within an initial letter series. While performing this task for trials spanning several seconds, both frontal midline theta and parietal alpha oscillations, which may subserve crucial functions of memory and cognition, constitute the dominant frequencies regardless of EEG reference or surface Laplacian transformation. However, the topographic maxima for theta at AFz and alpha at POz are largest for CSD-transformed spectra (Fig. 10A), resulting in focused CSD scalp distributions (Fig. 10B, C). In contrast, surface potential spectra render a less sharp, more distributed topography, which may include substantial spectral amplitudes at other sites (e.g., nose-referenced theta in Fig. 10B). For better comparison, EEG spectra were also plotted for nearby locations (i.e., at F3 for theta and at P3 for alpha). At these off-maximum sites, the smallest spectral amplitudes are seen for CSD estimates. Moreover, a small alpha peak can be observed at F3, which is most distinct for the average reference. It is also not a coincidence that low or zero spectral amplitudes (dark blue regions in Fig. 10B, C) can be seen over anterior regions (Nose, Nz) for the nose-referenced data but over lateral inferior temporal-parietal sites
