Imaging the columnar functional organization of human area MT+ to axis-of-motion stimuli using VASO at 7 Tesla

Abstract

Cortical columns of direction-selective neurons in the motion sensitive area (MT) have been successfully established as a microscopic feature of the neocortex in animals. The same property has been investigated at mesoscale (<1 mm) in the homologous brain area (hMT+, V5) in living humans by using ultra-high field functional magnetic resonance imaging (fMRI). Despite the reproducibility of the selective response to axis-of-motion stimuli, clear quantitative evidence for the columnar organization of hMT+ is still lacking. Using cerebral blood volume (CBV)-sensitive fMRI at 7 Tesla with submillimeter resolution and high spatial specificity to microvasculature, we investigate the columnar functional organization of hMT+ in 5 participants perceiving axis-of-motion stimuli for both blood oxygenation level dependent (BOLD) and vascular space occupancy (VASO) contrast mechanisms provided by the used slice-selective slab-inversion (SS-SI)-VASO sequence. With the development of a new searchlight algorithm for column detection, we provide the first quantitative columnarity map that characterizes the entire 3D hMT+ volume. Using voxel-wise measures of sensitivity and specificity, we demonstrate the advantage of using CBV-sensitive fMRI to detect mesoscopic cortical features by revealing higher specificity of axis-of-motion cortical columns for VASO as compared to BOLD contrast. These voxel-wise metrics also provide further insights on how to mitigate the highly debated draining veins effect. We conclude that using CBV–VASO fMRI together with voxel-wise measurements of sensitivity, specificity and columnarity offers a promising avenue to quantify the mesoscopic organization of hMT+ with respect to axis-of-motion stimuli. Furthermore, our approach and methodological developments are generalizable and applicable to other human brain areas where similar mesoscopic research questions are addressed.

Layered Structure of Cortex Explains Reversal Dynamics in Bistable Perception

“…Future work on layer specific responses and connectivity during bistable vision could help to further constrain our model. For example, the advent of ultra-high field fMRI allows us to investigate neural correlates of human cognition at columnar and laminar resolution [30, 45].…”

Characterisation of laminar and vascular spatiotemporal dynamics of CBV and BOLD signals using VASO and ME-GRE at 7T in humans

“…In recent years, this method (specifically slice-selective slab-inversion [SS-SI] VASO [Huber et al, 2014], henceforth referred to as VASO) has gained popularity for investigations of cortical depth-dependent signal changes at ultra-high fields ( > 7T) due to its high specificity to the microvasculature and hence the underlying neural activity (e.g. Faes et al, 2023; Haenelt et al, 2023; Huber et al, 2017; Koiso et al, 2023; Persichetti et al, 2020; Pizzuti et al, 2023; Yu et al, 2019; for other VASO variants at ultra-high field, see e.g. Chai et al, 2020; Hua et al, 2013).…”