Mapping directional functional connectivity across brain-wide networks with layer-specific CBV-fMRI

With recent advances in ultra-high field MRI contrast optimizations and acquisition strategies, it has become possible to measure cerebral blood volume (CBV)-weighted fMRI signal across cortical layers. While initial proof-of-principle layer-fMRI studies in primary brain areas with conventional fMRI task designs are promising (Polimeni 2010, Huber 2017-2019, De Martino 2015, Kok 2016, Koopmans 2010), layer-fMRI has not yet realized its full potential to map layer-dependent functional connectivity across large-scale brain networks (Finn 2018, Sharoh 2019). In this study, we investigate the applicability of CBV-weighted layer-fMRI to assess functional connectivity during naturalistic tasks without the biases of large draining veins. We can map common resting-state networks and characterize their internal layer-dependent signatures with respect to directionality and cortical hierarchy.

We find that layer-dependent fMRI is limited by SNR and venous signal leakage, making it challenging to map the functional connectome in humans. However, with the application of spatially specific CBV-weighted fMRI, we found that it is possible to measure functional connectivity across the entire brain without biases of venous signal leakage, yielding layer-dependent localization specificity.

It can be a valuable tool:
-> to obtain information about directional information flow across the entire brain
-> to reveal causal relationships in large scale networks