Layer Specific fMRI of the Human Superior Colliculi (SC)
We investigate the superior colliculi to reveal how human sensory processing is managed by this small mid-brain structure. Ultra-high fields are central to enable detailed detection of layer-specific fMRI signals.
Functional MRI of the human brain stem is challenging because of the proximity and small size of its functionally distinct brain nuclei. Using targeted fMRI techniques, that included point-spread-function correction, and a limited echo-train-length, we obtained EPI time-series with high spatial (1mm3 voxelsize) and temporal resolution (1s repetition time). Functional signals from regions-of-interests covering different zones at increasing depths of the superior colliculi revealed a characteristic pattern. Owing to a purely visual fMRI paradigm, lasting just 20min, the superficial zone clearly showed the highest signal. This finding was in accordance with current knowledge of the functional architecture of the SC. At 9.4T, the duration of the fMRI paradigm could be shortened to less than 1/3 than what is required at 3T. In addition, the depth dependence could be identified owing to the small voxels which were more than 4 times smaller than those used at 3T.