Layer-specific (f)MRI at high (3T) and ultra-high (7T) field strength

The human cerebral cortex has a well-known laminar structure that can be cytoarchitectonically divided into six different layers, ranging from layer I beneath the pial surface to layer VI above white matter.

 

Results from animal physiology indicate that different computational processes occur across these different layers1,2. In particular, feedback connections appear to originate from neurons mainly in deep layers (layer VI), and terminate mainly in layer I or in a combination of layers, but not in layer IV (granular layer)3,4. In contrast, forward connections originate in superficial cortical layers (layer II and III) and terminate in layer IV. This functional segregation according to cortical depth affords the exciting possibility to investigate in living human participants how bottom-up and top-down signals interact during perception and action.

 

The feasibility of layer-specific investigations in human subjects improves with increase in magnetic field strength. At high magnetic fields, fMRI benefits from increased BOLD based susceptibility contrast5,6 and higher signal-to-noise ratios (SNR)7,8. This permits the acquisition of images with higher spatial resolution and increased spatial specificity7,911. With increasing spatial resolutions, partial volume effects are reduced and the proportion of voxels that uniquely sample grey matter increases12. In cooperation with Professor Rainer Goebel from Maastricht University, we thus conduct experiments at field strength of both 3T and 7T.

 

Currently, we investigate how spatial attention modulates BOLD signal at three different cortical depth levels. One further goal is to correlate BOLD signal measured at different cortical depth levels with quantitative MR parameters (Magnetization Transfer, longitudinal relaxation time T1, Proton Density). This allows cross-validation and new insights into the structure-function relationship in human cortex.

 

Primary contacts

Marian Schneider (m.schneider «at» ucl.ac.uk)
Nikolaus Weiskopf (n.wieskopf «at» ucl.ac.uk)

 

References

[1]        Felleman, D. J. & Van Essen, D. C. Distributed hierarchical processing in the primate cerebral cortex. Cereb. Cortex N. Y. N 1991 1, 147 (1991).

[2]       Rockland, K. S. & Pandya, D. N. Laminar origins and terminations of cortical connections of the occipital lobe in the rhesus monkey. Brain Res. 179, 320 (1979).

[3]       Rockland, K. S., Saleem, K. S. & Tanaka, K. Divergent feedback connections from areas V4 and TEO in the macaque. Vis. Neurosci. 11, 579600 (1994).

[4]       Salin, P. A. & Bullier, J. Corticocortical connections in the visual system: structure and function. Physiol. Rev. 75, 107154 (1995).

[5]       Uğurbil, K. et al. Ultrahigh field magnetic resonance imaging and spectroscopy. Magn. Reson. Imaging 21, 12631281 (2003).

[6]       Yacoub, E. et al. Imaging brain function in humans at 7 Tesla. Magn. Reson. Med. Off. J. Soc. Magn. Reson. Med. Soc. Magn. Reson. Med. 45, 588594 (2001).

[7]       Olman, C. A. & Yacoub, E. High-field FMRI for human applications: an overview of spatial resolution and signal specificity. Open Neuroimaging J. 5, 7489 (2011).

[8]       Vaughan, J. T. et al. 7T vs. 4T: RF power, homogeneity, and signal-to-noise comparison in head images. Magn. Reson. Med. Off. J. Soc. Magn. Reson. Med. Soc. Magn. Reson. Med. 46, 2430 (2001).

[9]       Cheng, K., Waggoner, R. A. & Tanaka, K. Human ocular dominance columns as revealed by high-field functional magnetic resonance imaging. Neuron 32, 359374 (2001).

[10]       Yacoub, E., Harel, N. & Ugurbil, K. High-field fMRI unveils orientation columns in humans. Proc. Natl. Acad. Sci. 105, 1060710612 (2008).

[11]       Zimmermann, J. et al. Mapping the Organization of Axis of Motion Selective Features in Human Area MT Using High-Field fMRI. PLoS ONE 6, e28716 (2011).

[12]       De Martino, F. et al. Cortical Depth Dependent Functional Responses in Humans at 7T: Improved Specificity with 3D GRASE. PLoS ONE 8, e60514 (2013).

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