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Abstract:
We have studied the effects of eye movements on the functional magnetic resonance imaging (fMRI) response during global dot motion in extrastriate temporo-occipital cortex. Susceptibility-based functional magnetic resonance, applying gradient-recalled echo-planar imaging (EPI) sequences, was conducted, in 12 volunteers who viewed episodes of moving dots. Anatomical and functional images were recorded with a 1.5 T Siemens Magnetom Vision (TR 5000 ms, TE 70 ms, flip angle 90°, FOV 250 mm, matrix 112 × 128, twelve 4-mm slices parallel to ac — pc plane, ranging from z=-14 – 34 mm). Sagittal T1-weighted images were acquired to determine the ac — pc plane and important anatomical landmarks. Eye movements were monitored with the use of MR-compatible EOG electrodes. Stimuli were back-projected onto a translucent screen and viewed through prisms. The four test conditions were: fronto-parallel motion, during fixation and during target pursuit; expansion-contraction motion, also during fixation and during pursuit. Pixelwise t-tests were performed on functional series recorded during rest and stimulation periods (50 s each) to identify significantly activated voxels. Planes −8 to +8 mm around the ac — pc plane and 20 – 28 mm superior to ac — pc were activated most by visual motion. In addition to primary visual cortical areas, a ventral area in the temporo-occipital cortex (human MT) responded well to both types of visual motion and these responses were enhanced by eye movements. Human MST, located dorsal of MT, showed activation by visual motion during fixation. Its response was also enhanced by pursuit.
