Interdigitated Color- and Disparity-Selective Columns within Human Visual Cortical Areas V2 and V3

Abstract

In nonhuman primates (NHPs), secondary visual cortex (V2) is composed of repeating columnar stripes, which are evident in histological variations of cytochrome oxidase (CO) levels. Distinctive "thin" and "thick" stripes of dark CO staining reportedly respond selectively to stimulus variations in color and binocular disparity, respectively. Here, we first tested whether similar color-selective or disparityselective stripes exist in human V2. If so, available evidence predicts that such stripes should (1) radiate "outward" from the V1-V2 border, (2) interdigitate, (3) differ from each other in both thickness and length, (4) be spaced ϳ3.5-4 mm apart (center-to-center), and, perhaps, (5) have segregated functional connections. Second, we tested whether analogous segregated columns exist in a "next-higher" tier area, V3. To answer these questions, we used high-resolution fMRI (1 ϫ 1 ϫ 1 mm 3 ) at high field (7 T), presenting color-selective or disparity-selective stimuli, plus extensive signal averaging across multiple scan sessions and cortical surface-based analysis. All hypotheses were confirmed. V2 stripes and V3 columns were reliably localized in all subjects. The two stripe/column types were largely interdigitated (e.g., nonoverlapping) in both V2 and V3. Color-selective stripes differed from disparity-selective stripes in both width (thickness) and length. Analysis of resting-state functional connections (eyes closed) showed a stronger correlation between functionally alike (compared with functionally unlike) stripes/columns in V2 and V3. These results revealed a fine-scale segregation of color-selective or disparity-selective streams within human areas V2 and V3. Together with prior evidence from NHPs, this suggests that two parallel processing streams extend from visual subcortical regions through V1, V2, and V3.

How to choose the right MR sequence for your research question at 7 T and above?

“…This same technique was also employed to detect for the first time orientation dependent columns in humans with fMRI . More recently columnar structures have been found in auditory cortex (De Martino et al, 2015a) using 3D GRASE and stripes in V2 and V3 using gradient echo EPI (Nasr et al, 2016).…”

“…This is advantageous for spin-echo as the slice can include the pial surface without it contributing to the total signal. For gradient echo the signal from the pial signal has to be removed on the basis of its depth Nasr et al, 2016;Polimeni et al, 2010).…”

Geospatial statistics of high field functional MRI reveals topographical clustering for binocular stereo depth in early visual cortex

“…Over the past two years, two studies have investigated the fine-scale organization of disparity, one focusing on V3A and KO 27 , and the other on V2 and V3 28 , both providing some evidence for clustering of disparity responses.…”

A scalable method to improve gray matter segmentation at ultra high field MRI

“…The increase in SNR can be leveraged to increase the voxels' 6 resolution of both functional and structural images to sub-millimeter scales. Such function [9][10][11][12][13][14] and structure [5,8,15], (ii) the mapping of cortical columnar 10 structures [16][17][18][19][20][21] as well as (iii) sub-millimeter cortical topography [18,[22][23][24].…”

“…Assume an average thickness of human cortex of 2.4 mm and a true signal 18 change at the upper cortical depth level. In this study, the functional resolution would 19 allow a straight piece of cortical ribbon to be divided in three relative cortical depths, 20 each of them one voxel thick. Falsely labeling an additional fourth voxel as GM would 21 make the difference between reporting an fMRI signal change at most superficial (false 22 voxel excluded) or mid-superficial (false voxel included) cortical depth level.…”