Layer-specific response properties of the human lateral geniculate nucleus and superior colliculus

The human LGN and SC consist of distinct layers, but their layer-specific response properties remain poorly understood. In this fMRI study, we characterized visual response properties of the magnocellular (M) and parvocellular (P) layers of the human LGN, as well as at different depths in the SC. Results show that fMRI is capable of resolving layer-specific signals from the LGN and SC. Compared to the P layers of the LGN, the M layers preferred higher temporal frequency, lower spatial frequency stimuli, and their responses saturated at lower contrast. Furthermore, the M layers are colorblind while the P layers showed robust response to both chromatic and achromatic stimuli. Visual responses in the SC were strongest in the superficial voxels, which showed similar spatiotemporal and contrast response properties as the M layers of the LGN, but were sensitive to color and responded strongly to isoluminant color stimulus. Thus, the non-invasive fMRI measures show that the M and P layers of human LGN have similar response properties as that observed in non-human primates and the superficial layers of the human SC prefer transient inputs but are not colorblind.