Frontal and mesial temporal brain areas contribute to early visual evoked responses as revealed by electrical source imaging

Distributed EEG source imaging can reveal the electrical activity underlying visual perception in both cortical and deeper sources. How well electrical source imaging localizes functionally specialized visual areas, such as V1 and MT, has so far not been directly assessed. We used three functional localizer paradigms that are commonly used in fMRI to assess the localization accuracy for primary visual cortex, motion-sensitive areas, and face-sensitive areas. EEG source localization showed initial activations in striate and extrastriate areas at around 70 ms after stimulus onset that were quickly followed by extensive cortical, as well as subcortical activation. Functional motion and face-selective areas were successfully localized at around 170 and 150 ms respectively, with margins below 2 cm. The results furthermore show for the first time that the visually evoked C1 component has generators in the frontal eye fields and in mesial temporal areas, such as the parahippocampal gyrus.