A comparison of the localization of spontaneous neuromagnetic activity in the frequency and time domains

We investigated the localization of current sources for spontaneous magnetoencephalographic data in the frequency and time domains. The two analysis techniques yielded complementary information about the underlying neuronal generators. Phase-coherent sources for occipital 10 Hz alpha band activity were identified in the frequency domain from the dependence of the equivalent current dipole strengths on the phase of the Fourier transform. Source localization in both the frequency and time domains was used to analyze data containing interictal spike and slow-wave activity. Predominantly 2-6 Hz spectral components localized in the frequency domain were found within an 8 cm3 volume centered at the time-domain source location of the spike. In general, the characteristics of the noise sources in magnetoencephalographic systems favor the use of frequency-domain analysis for rhythmic spontaneous activity.