In the source montage 'Frontal Region' three different cortical surfaces of the left and right frontal lobe are contrasted against regional sources in 13 other brain regions. The 6 top signals marked by head symbols are equivalent to gross virtual electrodes placed on the left and right lateral frontal cortical surface (radial activities) and into fissures oriented towards midline and anterior (tangential activities).
Thus, the source currents of any direction in both lateral frontal lobes are largely separated from the activities in the other brain regions. The prominent alpha and theta rhythms are accounted for by the posterior and temporal sources and the frontal lobe signals become clearer. Thus, pattern search can be used to detect the frequent but very small spikes in this patient with cortical dysplasia. This finding is supported by concurrent spikes in the simultaneously recorded MEG (not shown here).
The serial maps show a rotation of the dipole field due to a small local propagation within the frontal lobe onto a cortical surface with different orientation. This finding becomes more obvious when spikes are averaged and the background alpha EEG is reduced.