Depth‐dependence of visual signals in the human superior colliculus at 9.4 T

Abstract

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. Hum Brain Mapp 38:574-587, 2017. © 2016 Wiley Periodicals, Inc.

Depth relationships and measures of tissue thickness in dorsal midbrain

“…However, several recent high-resolution fMRI studies using millimeter-scale voxels have demonstrated detailed analysis of the functional laminar topography of the human colliculi with reasonable CNR. Indeed, these studies have confirmed the functional properties of the three major layer groups of SC (Katyal & Ress, 2014;Linzenbold & Himmelbach, 2012;Loureiro et al, 2017;Savjani, Katyal, Halfen, Kim, & Ress, 2018;Schneider & Kastner, 2010), as well as the auditory organization of IC (De Martino et al, 2013;Moerel, De Martino, U gurbil, Yacoub, & Formisano, 2015;Ress & Chandrasekaran, 2013), encouraging interest in resolving these laminar variations of human colliculi in more detailed experiments. A recent fMRI study showed depth-dependent variations of the BOLD response with 1-mm sampling in SC (Loureiro et al, 2017).…”

Analysis strategies for high-resolution UHF-fMRI data

“…This approach has also been used to demonstrate that the across-subject variability of tonotopic maps in human primary auditory cortex, and the agreement between individual-subject maps and a recent model of the topographic layout, are both improved by removing gradient-echo BOLD voxels sampling the pial surface and considering only those voxels sampled away from these large draining vessels [Ahveninen et al , 2016]. Recent studies have similarly exploited the high-resolution afforded by UHF-fMRI to examine depth-dependent activation profiles and fine-scale functional organization within the hippocampus [Maass et al , 2014] and other subcortical structures [Loureiro et al. , 2017].…”

Ultra High Field fMRI of Human Superior Colliculi Activity during Affective Visual Processing

“…Because of their comparable size and adjacent anatomical location to those of the SC, the IC were selected as control regions to investigate the specificity of SC activity in response to visual stimulus processing. The masks were produced based on anatomical markers that delineate the SC and the IC from surrounding tissue 62 . The medial and posterior boundaries are demarcated respectively by the positions of the PAG 35 and of the cerebral spinal fluid identified on a region of high signal variability (see Fig.…”