Edwards, L.

Haenelt, D.

Helbling, S.

Nasr, S.

Pine, K.

Polimeni, J.

Sereno, M.

Tootell, R.

Trampel, R.

Weiskopf, N.

English

MPG.PuRe

Myelination Differences of Stripes in Human V2: Preliminary Evidence from 7 T Quantitative MRIDaniel Haenelt1,2, Robert Trampel1, Shahin Nasr3,4, Jonathan Polimeni3,4, Roger Tootell3,4, Martin Sereno5, Kerrin Pine1, Luke Edwards1, Saskia Helbling1,6, Nikolaus Weiskopf1,71Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2International Max Planck Research School on Neuroscience of Communication: Function, Structure, and Plasticity, Leipzig, Germany, 3Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA, 4Department of Radiology, Harvard Medical School, Charlestown, MA, USA, 5Department of Psychology, College of Sciences, San Diego State University, San Diego, CA, USA, 6Department of Neuroscience, Max Planck Institute for Empirical Aesthetics, Frankfurt, Germany, 7Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University, Leipzig, GermanyIntroductionResultsOHBM, 2021, Poster number: 217723The second visual area (V2) is known to contain a repea-ting pale-thin-pale-thick stripe pattern of cytochrome oxi-dase activity (CO). [1]Staining for myelin also reveals a stripe pattern in V2.However, it is still debated whether pale or dark stripes defined by CO are heavier myelinated. [2]Recent advances in ultra high field MRI enabled the func-tional delineation of V2 stripes in vivo. [3,4]In this study, we exploited the sensitivity of MRI to myelinand acquired high-resolution fMRI in conjunction with qMRI (R1, R2*) to infer myelination differences [5] bet-ween stripe types in humans.Our results show that V2 pale stripes are heavier myeli-nated than surrounding gray matter.4 volunteers participated in several scanning sessions over multiple days. Thin and thick stripes were functionally loca-lized by exploiting their different sensitivity to color and bi-nocular disparity, respectively, see Fig. 1. [4] Relaxation pa-rameters (R1, R2*) were determined from a high resolution MPM protocol. [6]haenelt@cbs.mpg.de14R1 in 1/s0.45 0.65V1V2MTCentral sulcusAuditoryAngular MT V2 V10.500.520.540.560.580.60R1 in s−1subj. 1subj. 2subj. 3subj. 4meanAngulargyrusz-score1.0 3.0V1V2V1V2V1/V2 borderV2/V3 border* *z-score1.0 5.0Color-selective thin stripes Disparity-selective thick stripesRH RH> >Robust mapping of thin and thick stripes in V2 — Activation maps of color-selective thin (a) and disparity-selective thick (b) stripes are shown for one representative participant. Maps are averaged across two ses-sions and sampled at mid-cortical depth using the equi-volume model [8]. Stripes running perpendicular to the V1/V2 border can be identified. Cyan dots are shown to illustrate the alternating stripe pattern in (a) vs. (b). Borders were manually defined based on separate retinotopy measurements. Black asterisks indi-cate the foveal region. RH: right hemisphere.Cortical R1 sampled at mid-cortex  — Data from one participant is shown in lateral (a) and posterior (b) view. Higher R1 values can be identified in primary motor and sensory areas as expected from the known heavier myelination of these areas. (c) Differences of mean R1 values between different cortical regions (angular gyrus, MT, V2, V1) defined by corresponding FreeSurfer labels for each participant also demon-strate the heavier myelination of V1 for all participants. Gray line: Mean across participants. Shaded area: 1 SD across participants.a b ca ba bHeavier myelination in pale stripes — Mean R1 (a)-(b) and R2* (c)-(d) values in thin (magenta) stripes, thick (cyan) stripes and whole V2 (gray) for several z-score threshold levels. The mean wascomputed across participants and hemispheres. Thin and thick stripe labels were defined by thresholding activation maps (see Fig. 2) at a specific z-score level. One stripe type was excluded in the definition for whole V2. Assuming a tripartite stripe division in V2, this allowed an indirect assessment of pale stripe contributions by comparing one stripe type to whole V2 excluding the other stripe type. [9] For each z = 0.0, 0.5, …, 4.5, the difference between thin/thick stripes and whole V2 was tested for statistical signifi-cance using permutation testing. [10] We find lower R1 (but not R2*) values in thin and thick stripes which point to heavier myeli-nation in pale stripes. Statistically significant differences are marked by asterisks, *: p<0.05, **: p<0.01, ***: p<0.001. Shaded area: 1 SEM.Visual stimuli — A block design with two experimentalconditions was used to map thin (a) and tick (b) stripesin V2. Further details can be found in [4].[1] Tootell RBH et al. Science 1983; 220:737.[2] Horton JC et al. Cereb Cortex 1997; 7:166.[3] Nasr S et al. J Neurosci 2016; 36:1841.[4] Dumoulin SO et al. Scientific Reports 2017; 7:1.[5] Edwards LJ et al. NeuroImage 2018; 182:184.[6] Weiskopf N et al. Front Neurosci 2013; 7:1.[7] Tabelow K et al. NeuroImage 2019; 194:191.[8] Waehnert MD et al. NeuroImage 2014; 93:210.[9] Li X et al. Cereb Cortex 2019; 29:544.[10] Burt JB et al. NeuroImage 2020; 220:1.ReferencesDiscussionMethodsExperimental designMRI data acquisitionAnalysisMeasurements were performed on a Siemens MAGNETOM7 T whole-body MR scanner (Siemens, Germany) using a 32-channel RF coil (Nova Medical, USA). For fMRI, we acqui-red an oblique-coronal slab (50 slices) using a GE-EPI proto-col (iso. 0.8 mm, TR =  3000 ms, TE = 24 ms, GRAPPA = 3, part. Fourier = 6/8). For qMRI, the MPM protocol consisted of2 multi-echo FLASH acquisitions with T1- and PD-weighting(iso. 0.5 mm, 6 echoes, TR = 25 ms, TE = 2-16 ms. GRAPPA = 2x2) plus maps of B1+ and B0. An optical tra-cking system was used (Kineticor, USA) to prospectively correct head motion during anatomical scans.Cortex segmentation was performed with FreeSurfer (6.0.0) on a separately acquired MP2RAGE scan. QMRIparameter maps were computed using the hMRI tool-box [7]. SPM12 was used for fMRI processing.Our results show that pale stripes in human V2 are heavier myelinated than surrounding gray matter which is in line with a recent MRI study in macaques. [9]Furthermore, we used qMRI parameter maps (R1, R2*) which are less biased by instrumental artefacts and better comparable across time, subjects and scanner sites than weighted images.This might be crucial to reliably measure small signal differen-ces over larger cortical areas.To the best of our knowledge, this is the first study whichdemonstrates the feasibility to infer myelination variationswithin a cortical area at the spatial scale of cortical columnsin living humans using qMRI.FundingThe research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° 616905.0 1 2 3 4z-score threshold0.5780.5800.5820.5840.5860.5880.5900.592Thin stripesV2 mean excludingthick stripesThick stripesV2 mean excludingthin stripesR1 in s⁻¹R2* in s⁻¹R1 in s⁻¹R2* in s⁻¹0 1 2 3 4z-score threshold0.5550.5600.5650.5700.5750.5800.585** ** ****** ***************************Comparison of R1 values between stripe typesComparison of R2* values between stripe typesa bc d0 1 2 3 4z-score threshold33.033.233.433.633.80 1 2 3 4z-score threshold33.233.433.633.834.034.2

Myelination differences of stripes in human V2: Preliminary evidence from 7 T quantitative MRI

http://hdl.handle.net/21.11116/0000-000B-400F-D

Myelination differences of stripes in human V2: Preliminary evidence from 7 T quantitative MRI

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