??Purpose: Neural microstimulation experiments in the superior colliculus (SC) of non-human primates have demonstrated a topographically organized representation of saccadic eye movements by neurons within the intermediate layers of the SC (Robinson, Vision Research, 12, 1972). A recent study using fMRI showed lateralization of saccade related activity in the human SC (Krebs et al., PLOS One, 5, 2010). Here, we examine the topographic representation of saccades in human SC. Methods: We used saccade targets (high-contrast 0.5?° dots) that could appear anywhere within a wedge-shaped region (eccentricity 4a??10?°, azimuthal width 12?°) that slowly rotated (48-s period) around the fixation mark. Subjects made alternating centrifugal and centripetal saccades to the eccentric and fixation targets respectively while performing a shape discrimination task (square or triangle) within each target with each trial lasting 0.8 seconds. High-resolution fMRI (1.2 mm voxels, 3-shot spiral, TE = 40 ms) was acquired (3 s/volume) in 8 slices that covered the whole of the SC. Results: We observed that the polar angle of the saccade directions was represented upon both left and right SC, with the upper-lower visual field mapped in a roughly mediolateral direction, within a narrow band along the rostrocaudal direction. Preliminary results suggest that the maps agree well with previous measurements the representation of visual stimulation in the superficial layers of human SC (Katyal et al., J Neurophysiol, in press). Depth profiles of the activity suggest that the activity peaks slightly below the superficial surface of the SC. Conclusions: High-resolution fMRI can resolve retinotopic maps of saccadic eye movements in the intermediate layers of human SC. The observed topography is similar to that observed in non-human primates.
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