The Breakfast and Science Seminar #7, held on 25th August, featured two presentations of CIBM research. 

The first talk was given by Gabriel Girard. The second talk represents a long-standing research collaboration which started in 2015 between Dr. Gregoire Wuerzner, MD, Dr. Marielle Hendricks-Balk at the Lausanne University Hospital (CHUV) and CIBM research staff scientists Dr. Domenica Bueti, who is now a Professor at SISSA in Trieste, and continued with Dr. Sandra Borges Da Costa in 2016.


On the cortical connectivity in the macaque brain: a comparison of diffusion tractography and histological tracing data

Gabriel Girard,
Research Staff Scientist, CIBM SP CHUV-EPFL Section & Postdoctoral researcher Department of Radiology, Lausanne University Hospital (CHUV)

Abstract: Diffusion-weighted magnetic resonance imaging (DW-MRI) tractography is a non-invasive tool to probe neural connections and the structure of the white matter. Recent work has revealed that tractography produces a high incidence of false-positive connections, often from bottleneck white matter configurations. The rich literature in histological connectivity analysis studies in the macaque monkey enables quantitative evaluation of the performance of tractography algorithms. In this study, we use the intricate connections of frontal, cingulate, and parietal areas, well established by the anatomical literature, to derive a symmetrical histological connectivity matrix composed of 59 cortical areas. We evaluate the performance of fifteen diffusion tractography algorithms, including global, deterministic, and probabilistic state-of-the-art methods for the connectivity predictions of 1,711 distinct pairs of areas, among which 680 are reported connected by the literature. The diffusion connectivity analysis was performed on a different ex-vivo macaque brain, acquired using multi-shell DW-MRI protocol, at high spatial and angular resolutions. Across all tested algorithms, the true-positive and true-negative connections were dominant over false-positives and false-negative connections, respectively. Overall, those results confirm the usefulness of tractography in predicting connectivity, although errors are produced. Many of the errors result from bottleneck white matter configurations near the cortical grey matter and should be the target of future implementation of methods.

Ultra-high field fMRI brainstem investigation in relation to blood pressure control

Mariëlle Hendriks-Balk,
Clinical Research Collaborator, Service de néphrologie et hypertension, Centre Hospitalier Universitaire Vaudois CHUV, Lausanne


Abstract: Modern imaging techniques such as blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) allow the non-invasive and indirect measurement of brain activity. Whether changes in signal intensity can be detected in small brainstem regions during a stress test, that increases blood pressure, has not been explored thoroughly. The aim of our study was to measure whole brain and brainstem BOLD signal intensity changes in response to a modified cold pressure test (CPT). In a pilot study BOLD fMRI was measured in 11 healthy normotensive participants during a randomized crossover study (modified CPT vs. control test) using ultra-high field 7 Tesla MRI scanner. Data were analyzed using Statistical Parametric Mapping (SPM) in a whole-brain approach, and with a brainstem-specific analysis using the spatially unbiased infra-tentorial template (SUIT) toolbox. Blood pressure (BP) and hormonal responses (norepinephrine and epinephrine levels) were also measured. BP increased during the CPT. Whole-brain analysis revealed significant activations linked to the CPT in the right supplementary motor cortex, midcingulate (bilateral) and the right anterior insular cortex. The brainstem-specific analysis showed significant activations in the dorsal medulla. These results open up new ways to explore and acquire new insights in the comprehension of neurogenic hypertension. Based on these results we adapted and optimized our paradigm of stimulation, the image acquisition and the image processing to get more precise data for the brainstem and the whole brain of both healthy subjects and hypertensive patients.

The monthly meet-up seminar series is a great environment to ask questions or to share insights on challenges and solutions. It’s also a good way to broaden and enrich professional networks.

The next Breakfast and Science Seminar #8 will be held on September 29th.

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