Seminar - Dr Andreea Hertanu "Diffusion MRI as a microstructural and functional probe for cortical Gray Matter"

Seminar of Dr Andreea Hertanu, Dep of Radiology, Microstructure mapping Lab, Lausanne, Switzerland

The seminar will take place on Mai 23-rd at 2:00 PM – l'amphithéâtre Ruch (first floor - Faculté de Chirurgie Dentaire).

Title: Diffusion MRI as a microstructural and functional probe for cortical Gray Matter

Abstract: Owing to its sensitivity to restrictions and hindrances in the form of cell membranes or sub-cellular structures encountered by diffusing water molecules, diffusion MRI (dMRI) facilitates the exploration of microstructural features within the brain. As such, alterations in cell morphology and water transport mechanisms linked to neuronal activity are inherently embedded in the dMRI signal. In this context, our goal was to investigate changes in Mean Diffusivity (MD) and Mean Kurtosis (MK) and their time-dependence across the rat brain upon unilateral forepaw electrical stimulation. The positive BOLD response in the contralateral primary somatosensory cortex, forelimb region (S1FL) was accompanied by a significant decrease in MD, described in the literature as the result of cellular swelling and increased tortuosity in the extracellular space. For the first time, we are also reporting a paired decrease in MK during stimulation in S1FL, most likely indicative of increased membrane permeability, as suggested by the slight decrease in exchange time estimated from time-dependence analyses. Other cortical and subcortical brain regions involved in somatosensory processing and integration were investigated. However, changes in MD and MK did not parallel changes in the BOLD signal in a systematic way, and more surprisingly, subcortical somatosensory relays such as the thalamus and the hippocampus displayed increased MD and MK in the absence of a BOLD response. Our results reflect a disconnection of underlying functional contrast sources between diffusion weighting and BOLD and highlight the capacity of dMRI to offer complementary functional insights into neural activity, potentially below the BOLD detection threshold