VASO reveals distinct layer-connectivity between digit-representations in BA3b

Poster No:

1634 

Submission Type:

Abstract Submission 

Authors:

Sebastian Dresbach1, Renzo Huber1, Rainer Goebel1, Amanda Kaas1

Institutions:

1Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Limburg

First Author:

Sebastian Dresbach  
Faculty of Psychology and Neuroscience, Maastricht University
Maastricht, Limburg

Co-Author(s):

Renzo Huber  
Faculty of Psychology and Neuroscience, Maastricht University
Maastricht, Limburg
Rainer Goebel  
Faculty of Psychology and Neuroscience, Maastricht University
Maastricht, Limburg
Amanda Kaas  
Faculty of Psychology and Neuroscience, Maastricht University
Maastricht, Limburg

Introduction:

Inter-digit interactions are crucial for manual abilities like tool use or object manipulation. However, digits seem to be distinctly represented in subareas of the primary somatosensory cortex (S1). In non-human primates, interactions between digits have been demonstrated within and between representations in subregions of S1 during stimulation and resting-state (RS). However, there is little evidence on the mechanisms behind these interactions and whether similar processes can be found in humans. One outstanding issue with respect to the application of this research to humans is the necessary specificity of non-invasive (fMRI) measurements. In contrast to the commonly used BOLD-signal, which is heavily biased towards the pial surface, slice-selective slab-inversion vascular space occupancy (VASO) might fulfil this need. Therefore, we aim to use VASO to map individual digit-representations in human subjects during stimulation and explore their intrinsic interactions at rest.

Methods:

5 subjects underwent scanning using a "classical" 7T Magnetom whole body scanner (Siemens Healthineers, Erlangen, Germany), equipped with a Rx 32-channel head coil at Scannexus (Maastricht, The Netherlands). All functional scans were performed with 3D-EPI, VASO (nominal resolution=0.75x.075x1.29mm,22 slices,TI1/TI2/TR/TE=50/650/2269/25ms,part. fourier factor=6/8, flip angle=4°,bandwidth=1064Hz/Px,FoV=122mm). Slice position and orientation were chosen individually for each subject and covered the postcentral gyrus while optimising resolution perpendicular to its anterior bank. Finally, 3 high-resolution anatomical MP2RAGE-slabs (0.5mm isotropic,60 slices,TI1/TI2/TR/TE=900/2750/6000/4.02ms, flip angle1=6°,flip angle2=7°,bandwidth=140Hz/Px,acceleration factor=2,FoV=160mm) were acquired with the same coverage.
During stimulation runs (~12 minutes), 3 digit-tips (fig. 1A) were stimulated (30s on-off block design, 4 repetitions/digit) with a vibrotactile stimulator (mini PTS, Dancer Design, UK). During subsequent RS scans, subjects were instructed to lay comfortably with their eyes open.
Motion- and BOLD-correction was applied using ANTs-Registration and LayNii, respectively. GLM-analyses were performed in FSL, a ROI for each digit was manually drawn in FSLeyes. Finally, layering and signal extraction was performed on spatially upsampled data (0.1x0.1x1.29mm).

Results:

Fig. 1B shows zmaps and ROIs of a representative subject.
Fig. 1C shows the layer-profiles per ROI resulting from finger-stimulation across all subjects. Profiles corresponding to the stimulated digit show a peak in middle layers for VASO- and a peak drawn towards the superficial layers for BOLD-signal. The former likely reflects the input to the granular layer from the thalamus, while the BOLD-signal is dominated by draining veins on the pial surface.
In order to investigate the depth-dependent correlations between digit-ROIs, we extracted RS-signal from 3 layers (fig. 2A) of each ROI (i.e. 9 per subject). We ran GLMs containing single time-courses as predictors and extracted beta-values across layers for the two non-seed ROIs. Finally, profiles from all ROIs were averaged per seed-depth.
fig. 2B shows that superficial layers of a given ROI are correlated with superficial layers of other ROIs, while deep layers of a given ROI are correlated with deep layers of other ROIs. There was no depth-effect for middle-layer seeds. These results are not likely to be a result of differences in tSNR (fig. 2C).
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Supporting Image: ScreenShot2021-02-01at175545.png
 

Conclusions:

Here, we show the applicability of VASO in the investigation of digit-specific representations in S1. Furthermore, we demonstrated the specificity of the technique by showing that, in contrast to the BOLD-signal, activation-peaks can be seen in middle layers, as expected based on input-output characteristics of the canonical microcircuit. Finally, we provide initial results towards the implication of distinct patterns of layer-connectivity across depth between functionally related patches of cortex.

Modeling and Analysis Methods:

Activation (eg. BOLD task-fMRI)
Connectivity (eg. functional, effective, structural)
Task-Independent and Resting-State Analysis

Novel Imaging Acquisition Methods:

Non-BOLD fMRI 2

Perception, Attention and Motor Behavior:

Perception: Tactile/Somatosensory 1

Keywords:

Cortical Layers
FUNCTIONAL MRI
HIGH FIELD MR
Perception
Somatosensory
Other - VASO; 7T

1|2Indicates the priority used for review

My abstract is being submitted as a Software Demonstration.

No

Please indicate below if your study was a "resting state" or "task-activation” study.

Resting state
Task-activation

Healthy subjects only or patients (note that patient studies may also involve healthy subjects):

Healthy subjects

Was any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

Yes

Was any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.

Not applicable

Please indicate which methods were used in your research:

Functional MRI

For human MRI, what field strength scanner do you use?

7T

Which processing packages did you use for your study?

FSL
Other, Please list  -   LayNii

Provide references using author date format

Felleman D.J. (1991), 'Distributed hierarchical processing in the primate cerebral cortex', Cerebral Cortex. 1(1): 1–47.
Jones, E.G. (1978), 'Intracortical connectivity of architectonic fields in the somatic sensory, motor and parietal cortex
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Huber L. (2014), 'Slab-selective, BOLD-corrected VASO at 7 Tesla provides measures of cerebral blood volume
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Hsiao S. (2008), 'Central mechanisms of tactile shape perception. Current Opinion in Neurobiology' 18(4): 418–424.
Marques J.P. (2010) 'MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at
high field', Neuroimage 49: 1271–1281.
Poser B.A. (2010), 'Three dimensional echo-planar imaging at 7 Tesla', NeuroImage. 51(1): 261–266.
Wang Z. (2013), 'The Relationship of Anatomical and Functional Connectivity to Resting-State Connectivity in
Primate Somatosensory Cortex', Neuron 78(6): 1116–1126.