Synopsis

Keywords: Neuro: Brain function

This lecture will focus on VASO and diffusion-fMRI as methods imparting enhanced specificity on the funtional MRI signal.

The Blood Oxygenation Level Dependent (BOLD) mechanism plays a central role in contemporary noninvasive functional neuroimaging. By relying on neurovascular coupling mechanisms, BOLD contrasts are able to portray brain areas engaged in processing e.g. external stimuli or map resting-state networks. However, the neurovascular coupling can suffer from decreased specificity with respect to the underyling neural signals, both spatially (due to recruitement of vessels distant from activation foci) and temporally (due to the low-pass nature of neurovascular coupling). In the talk, we will discuss means for enhancing the specificity of BOLD-fMRI, both in terms of spatial specificity and temporal order. We will first describe VASO-fMRI as means of filtering neurovascular responses such that they provide enhanced spatial specificity, and then quickly describe ultrafast fMRI methods capable of mapping neural input order from BOLD onsets. We will then move to diffusion-fMRI (dfMRI), which aims to depart from neurovascular coupling and rather rely on a different coupling mechanisms, namely, the neuro-morphological coupling. We will describe evidence for neuromorphological coupling, and then discuss Le Bihan's proposal of their measurement via dfMRI. Several more recent experiments suggesting that dfMRI's mechanism is indeed coupled to activity-driven changes in microstructure will also be presented.

Acknowledgements

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References

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