The aim of the present study is to investigate the spatial resolution of electroencephalography (EEG) cortical source imaging by localizing the retinotopic organization in the human primary visual cortex (V1). Retinotopic characteristics in V1 obtained from functional magnetic resonance imaging (fMRI) study were used as reference to assess the spatial resolution of EEG since fMRI can discriminate small changes in activation in visual field. It is well known that the activation of the early C1 component in the visual evoked potential (VEP) elicited by pattern onset stimuli coincides well with the activation in the striate cortex localized by fMRI. In the present experiments, we moved small circular checkerboard stimuli along horizontal meridian and compared the activations localized by EEG cortical source imaging with those from fMRI. Both fMRI and EEG cortical source imaging identified spatially correlated activity within V1 in each subject studied. The mean location error, between the fMRI-determined activation centers in V1 and the EEG source imaging activation peak estimated at equivalent C1 components (peak latency: 74.8 ± 10.6 ms), was 7 mm (25% and 75% percentiles are 6.45 mm and 8.4 mm, respectively), which is less than the change in fMRI activation map by a 3° visual field change (7.8 mm). Moreover, the source estimates at the earliest major VEP component showed statistically good correlation with those obtained by fMRI. The present results suggest that the spatial resolution of the EEG cortical source imaging can correctly discriminate cortical activation changes in V1 corresponding to less than 3° visual field changes.
Bibliographical noteFunding Information:
We thank John Swain, Cameron Sheikholeslami, and Varun Garg for assistance in VEP experimentation, and the anonymous reviewers for constructive comments to the original version of the manuscript. This work was supported in part by NSF BES-0411898, NIH RO1 EB00178, NIH RO1 EB00239, the Biomedical Engineering Institute of the University of Minnesota, BTRR P41 008079, KECK Foundation and MIND Institute. CH Im was supported in part by a Korea Research Foundation Fellowship funded by the Korean Government (MOEHRD) (M01-2005-000-10132-0).
- Cortical source imaging
- Primary visual cortex (striate cortex or V1)
- Retinotopic organization
- Visual evoked potential