Point-spread function of the BOLD response across columns and cortical depth in human extra-striate cortex.

Alessio Fracasso,Serge O Dumoulin,Natalia Petridou

doi:10.1016/j.pneurobio.2021.102187

Abstract

Columns and layers are fundamental organizational units of the brain. Well known examples of cortical columns are the ocular dominance columns (ODCs) in primary visual cortex and the column-like stripe-based arrangement in the second visual area V2. The spatial scale of columns and layers is beyond the reach of conventional neuroimaging, but the advent of high field magnetic resonance imaging (MRI) scanners (UHF, 7 Tesla and above) has opened the possibility to acquire data at this spatial scale, in-vivo and non-invasively in humans. The most prominent non-invasive technique to measure brain function is blood oxygen level dependent (BOLD) fMRI, measuring brain activity indirectly, via changes in hemodynamics. A key determinant of the ability of high-resolution BOLD fMRI to accurately resolve columns and layers is the point-spread function (PSF) of the BOLD response in relation to the spatial extent of neuronal activity. In this study we take advantage of the stripe-based arrangement present in visual area V2, coupled with sub-millimetre anatomical and gradient-echo BOLD (GE BOLD) acquisition at 7 T to obtain PSF estimates and along cortical depth in human participants. Results show that the BOLD PSF is maximal in the superficial part of the cortex (1.78 mm), and it decreases with increasing cortical depth (0.83 mm close to white matter).

Highlights

The cortical column is a prominent organizational feature in primary visual cortex (V1) at the mesoscopic, i.e. millimetre, organization level, and is hypothesized to be a generic organizational feature across the whole human brain (Dumoulin et al, 2017)
Results show that the blood oxygen level dependent (BOLD) point-spread function (PSF) is maximal in the superficial part of the cortex (1.78 mm), and it decreases with increasing cortical depth (0.83 mm close to white matter)
Overall gradient-echo BOLD (GE BOLD) PSF is maximal in the superficial part of the cortex, and it decreases with increasing cortical depth

Summary

Introduction

The cortical column is a prominent organizational feature in primary visual cortex (V1) at the mesoscopic, i.e. millimetre, organization level, and is hypothesized to be a generic organizational feature across the whole human brain (Dumoulin et al, 2017). The cortical col umn is characterized by fine-scale functional specializations, for example V1 neurons responding preferentially to monocular input coming to the left and right eyes are segregated in distinct ocular dominance columns (ODCs). Data from macaque neurophysiology and human neuro imaging indicates that different visual features are processed in distinct streams, segregated both functionally and anatomically. We have shown that the functional and anatomical properties of V2 stripes are related (Dumoulin et al, 2017)

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