Comparative study of human retinotopy using MEG and fMRI

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ABSTRACT.In order to visualize the human retinotopy in vivo we compared the source location of P100m dipoles in visual evoked magnetic fields (VEFs) with the activated area obtained by functional magnetic resonance imaging (fMRI) with EPI method. Checkerboard reversal pattern stimulation was presented to the left and right hemifields, and to the upper and lower quadrant fields of five normal subjects. VEF were recorded using a 129-channel vector neuromagnetic imaging system (Shimadzu Co., SBI-l00). fMRI was obtained by a conventional 1.5T MRI scanner from the same subject using echo planar imaging sequence. In half-field stimulation, the source location of P100m was estimated on the contralateral calcarine sulcus. The location of equivalent current dipole (ECD) in lower quadrant stimuli was below calcarine sulcus. In fMRI, the activated area in half-field stimuli was situated in the lingual gyrus below the contralateral calcarine fissure. However, the activated areas in quadrant stimuli were situated around the posterior part of the contralateral lingual gyrus. Our results show that the locations of ECDs in pattern reversal VEFs roughly agree with the activated area in fMRI.The reliability of source localization of P100m must be reinforced by a fMRI study.