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. Author manuscript; available in PMC: 2016 Sep 1.
Published in final edited form as: Int J Psychophysiol. 2015 Apr 25;97(3):189–209. doi: 10.1016/j.ijpsycho.2015.04.012

Figure 15.

Figure 15

Ratio of scalp measure to cortical potential as a function of dipole layer size. A, B: Vertex scalp potentials for a 81-channel 10–10 system EEG montage (average reference) due to simulated dipole layers of varying angular extent, forming superficial spherical caps in a four-shell forward solution (Berg, 2006) for two different ratios of brain-to-skull conductivity with the following conductivities [S/m]: brain = 0.33, skull = 0.0042 (A: ratio = 78.6) or 0.0084 (B: ratio = 39.3), CSF = 1.0, scalp = 0.33. C, D: Corresponding surface Laplacian estimates (CSD: current source density) using spherical splines of different flexibility (m = 2–7; λ = 10−5; Perrin et al., 1989). Note that surface potentials are primarily sensitive to broad dipole layers, whereas the sensitivity of spherical spline surface Laplacian estimates varies with spline flexibility.