In Vivo Identification of Thick, Thin, and Pale Stripes of Macaque Area V2 Using Submillimeter Resolution (f)MRI at 3 T.

Xiaolian Li,Wim Vanduffel,Thomas Janssens,Qi Zhu,John T Arsenault

doi:10.1093/cercor/bhx337

Xiaolian Li, Wim Vanduffel + Show 3 more

Open Access

https://doi.org/10.1093/cercor/bhx337

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Abstract

Primate area V2 contains a repetitive pattern of thick, thin and pale cytochrome oxidase stripes that are characterized by largely discrete in- and output channels, as well as differences in function, and myelo- and cytoarchitecture. Stripes have been identified mainly using microscope-based imaging of tiny portions of superficially located V2, or by postmortem methods, hence, the quest for (quasi) noninvasive tools to study these mesoscale functional units. Only recently, stripe-like V2 patterns have been demonstrated in humans with high-field (functional) magnetic resonance imaging (f)MRI, but in both such studies only 2 stripe compartments could be identified. Although interstripe distances in monkeys are ~half of those in humans, we show that all 3 V2 stripe classes can be reliably separated using submillimeter (f)MRI (0.6 mm isotropic voxels) on regular 3 T scanners by combining contrast agents and implanted phased-array coils. Specifically, we show highly reproducible fMRI patterns, both within and across subjects, of color-selective thin and disparity-selective thick stripes. Furthermore, reliable MRI-based higher myelin-density was observed in pale stripes. Hence, this is the first study showing segregation of columns using (f)MRI-based methods in macaque cortex, which opens the possibility of studying these elementary building blocks of the visual system noninvasively on a large scale.

Highlights

Visual information is transmitted from retina to cortex through multiple parallel channels
The retinotopic definition of the rostral border of V2d is less straightforward in macaque monkeys, since a noncontinuous retinotopic organization has been reported immediately rostral to V2d (Gattass et al 1988)
We found that the median myelin densities in both color and disparity stripes was significantly lower than that observed in randomly selected vertices of V2d (P-values < 0.05)

Summary

Introduction

Visual information is transmitted from retina to cortex through multiple parallel channels. Early visual cortical areas are characterized by subcompartments that can be differentiated based on their in- and outputs and the corresponding anatomical (cyto- and myeloarchitecture) and functional differences These mesoscale functional compartments are oriented either parallel (in layers) or orthogonal (in columns) to the cortical surface and allow partially segregated processing of, for example, color, orientation, disparity, and motion signals in the early visual stages. In the second visual area (V2) of monkeys and humans, 3 column-like functional subdivisions have been described using cytochrome oxidase (CO) staining (Tootell et al 1983; Horton 1984; DeYoe and Van Essen 1985; Hockfield et al 1990): the CO-dark thin, CO-light pale (or inter), and CO-dark thick stripes. Since different staining methods for myelin can yield conflicting results (Horton and Hocking 1997), it remains unclear whether higher myelin densities should be attributed to pale, thick, or thin strips (Krubitzer and Kaas 1989; Tootell and Taylor 1995)

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