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Keith A. Schneider, Marlene C. Richter, Sabine Kastner; Retinotopic organization and functional subdivisions of the human lateral geniculate nucleus and superior colliculus. Journal of Vision 2004;4(8):284. doi: 10.1167/4.8.284.
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Purpose: The lateral geniculate nucleus (LGN) and superior colliculus (SC) are small subcortical visual structures. We demonstrate the feasibility of measuring their retinotopy and discriminating the magnoceullular (M) and parvocellullar (P) layers of the LGN using functional magnetic resonance imaging (fMRI) in humans. Methods: High-contrast flickering (8 Hz) and periodic (1/32 Hz) checkerboard stimuli, rotating hemifields and expanding rings, were presented in separate sessions to 7 subjects to obtain polar angle and eccentricity maps, respectively. In a third session, alternating hemifield stimuli of 100% or 10% luminance contrast were presented to attempt to discriminate the M and P layers of the LGN. 128 volumes (18 interleaved coronal slices 2 mm thick, no gap) were acquired with a 3 T scanner, birdcage head coil and a standard EPI sequence (TR = 2 s, TE = 41 ms, FA = 90°, 128 matrix, in-plane resolution 1.5 × 1.5 mm). The volumes were motion-corrected and averaged over 6–12 scanning runs, and the phases of each voxel's responses were calculated with a Fourier analysis. Results: Adjacent voxels in the LGN exhibited distinct response phases, yielding highly consistent retinotopic maps across subjects. The lower contralateral hemifield was represented medially and superiorly, and the upper contralateral hemifield was represented laterally and inferiorly. The fovea was represented posteriorly, with eccentricity increasing anteriorly. The volumetric eccentricity magnification factor was similar to that in V1. Based on their contrast responses, LGN voxels containing mostly M cells were localized to the inferior and medial surfaces. In the SC, contralateral activation was observed, but no consistent further organization could be resolved. Conclusions: Robust measurement of the LGN and SC topography is possible using high-resolution fMRI due to a reduced partial volume effect. Resolving the LGN in humans on the scale of its individual layers has many applications.
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