Depth-Dependence of Visual Signals in the Human Superior Colliculus at 9.4 T

Activation maps obtained in each subject for 20 min functional measurement of hemifield activation, thresholded at p < 0.001 (uncorrected) for illustrative purposes and the corresponding zoomed images of the SC for each subject. Two different contrasts are shown: yellow is the contrast for right hemifield stimulation versus baseline and red for left hemifield stimulation versus baseline. The orange color shows areas with overlapping left‐right activations.

The superior colliculus (SC) is a layered structure located in the midbrain. We exploited the improved spatial resolution and BOLD signal strength available at 9.4 T to investigate the depth profile of visual BOLD responses in the human SC based on distortion-corrected EPI data with a 1 mm isotropic resolution. We used high resolution (350 µm in-plane) anatomical images to determine regions-of-interest of the SC and applied a semi-automated method to segment it into superficial, intermediate, and deep zones. A greater than linear increase in sensitivity of the functional signal at 9.4 T allowed us to detect a statistically significant depth pattern in a group analysis with a 20 min stimulation paradigm. Descriptive data showed consistent depth profiles also in single individuals. The highest signals were localized to the superficial layers of the right and left SC during contralateral stimulation, which was in good agreement with its functional architecture known from non-human primates. This study thus demonstrates the potential of 9.4 T MRI for functional neuroimaging even in deeply located, particularly challenging brain structures such as the SC.

Joana R Loureiro, Gisela E Hagberg, Thomas Ethofer, Michael Erb, Jonas Bause, Philipp Ehses, Klaus Scheffler, Marc Himmelbach:
Depth-dependence of visual signals in the human superior colliculus at 9.4 T.
Hum Brain Mapp. 2017 Jan;38(1):574-587.
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