Laminar analysis of the cerebellar cortex shows widespread damage in early MS patients: A pilot study at 7T MRI.

BACKGROUND: To date, little is known about the presence and extent of cerebellar cortical pathology in early stages of MS. OBJECTIVE: The aims of this study were to (i) investigate microstructural changes in the normal-appearing cerebellar cortex of early MS patients by using 7 T MRI and (ii) evaluate the influence of those changes on clinical performance. METHODS: Eighteen RRMS patients and nine healthy controls underwent quantitative T1 and T2* measurement at 7 T MRI using high-resolution MP2RAGE and multi-echo gradient-echo imaging. After subtracting lesion masks, average T1 and T2* maps were computed for three layers in the cerebellar cortex and compared between groups using mixed effects models. RESULTS: The volume of the cerebellar cortex and its layers did not differ between patients and controls. In MS patients, significantly longer T1 values were observed in all vermis cortical layers and in the middle and external cortical layer of the cerebellar hemispheres. No between-group differences in T2* values were found. T1 values correlated with EDSS, SDMT and PASAT. CONCLUSIONS: We found MRI evidence of damage in the normal-appearing cerebellar cortex at early MS stages and before volumetric changes. This microstructural alteration appears to be related to EDSS and cognitive performance.

Whole-body somatotopic maps in the cerebellum revealed with 7T fMRI.

The cerebellum is known to contain a double somatotopic body representation. While the anterior lobe body map has shown a robust somatotopic organization in previous fMRI studies, the representations in the posterior lobe have been more difficult to observe and are less precisely characterized. In this study, participants went through a simple motor task asking them to move either the eyes (left-right guided saccades), tongue (left-right movement), thumbs, little fingers or toes (flexion). Using high spatial resolution fMRI data acquired at ultra-high field (7T), with special care taken to obtain sufficient B1 over the entire cerebellum and a cerebellar surface reconstruction facilitating visual inspection of the results, we were able to precisely map the somatotopic representations of these five distal body parts on both subject- and group-specific cerebellar surfaces. The anterior lobe (including lobule VI) showed a consistent and robust somatotopic gradient. Although less robust, the presence of such a gradient in the posterior lobe, from Crus II to lobule VIIIb, was also observed. Additionally, the eyes were also strongly represented in Crus I and the oculomotor vermis. Overall, crosstalk between the different body part representations was negligible. Taken together, these results show that multiple representations of distal body parts are present in the cerebellum, across many lobules, and they are organized in an orderly manner.

Metabolite concentration changes associated with positive and negative BOLD responses in the human visual cortex: A functional MRS study at 7 Tesla.

Negative blood oxygenation-level dependent (BOLD) signal observed during task execution in functional magnetic resonance imaging (fMRI) can be caused by different mechanisms, such as a blood-stealing effect or neuronal deactivation. Electrophysiological recordings showed that neuronal deactivation underlies the negative BOLD observed in the occipital lobe during visual stimulation. In this study, the metabolic demand of such a response was studied by measuring local metabolite concentration changes during a visual checkerboard stimulation using functional magnetic resonance spectroscopy (fMRS) at 7 Tesla. The results showed increases of glutamate and lactate concentrations during the positive BOLD response, consistent with previous fMRS studies. In contrast, during the negative BOLD response, decreasing concentrations of glutamate, lactate and gamma-aminobutyric acid (GABA) were found, suggesting a reduction of glycolytic and oxidative metabolic demand below the baseline. Additionally, the respective changes of the BOLD signal, glutamate and lactate concentrations of both groups suggest that a local increase of inhibitory activity might occur during the negative BOLD response.

Whole brain measurements of the positive BOLD response variability during a finger tapping task at 7 T show regional differences in its profiles.

PURPOSE: The positive BOLD response can vary across brain regions. Here, the positive BOLD responses of motor regions, including the cerebellum, were investigated by fast fMRI acquisition. METHODS: The participants were asked to perform an event-related finger-tapping task in a 7T MRI scanner during a fast 3D-EPI controlled aliasing in parallel imaging acquisition protocol (CAIPI; TR = 399 ms). The positive BOLD responses of 6 motor regions were extracted and their timings and shapes measured. RESULTS: Compared with other brain regions, the positive BOLD responses in the cerebellum and secondary somatosensory cortex showed delayed onsets, but no differences were observed for the time to-peak. Additionally, variations of the undershoot and main peak amplitudes were also observed, and undershoot was quasi-absent in the cerebellum. CONCLUSION: This study confirms that care should be taken when drawing conclusions about neuronal activity from the BOLD signal, particularly for the cerebellum.

Surface-based characteristics of the cerebellar cortex visualized with ultra-high field MRI.

Although having a relatively homogeneous cytoarchitectonic organization, the cerebellar cortex is a heterogeneous region characterized by different amounts of myelin, iron and protein expression profiles. In this study, we used quantitative T1 and T2* mapping at ultra-high field (7T) MRI to investigate the tissue characteristics of the cerebellar gray matter surface and its layers. Detailed subject-specific surfaces were generated at three different cortical depths and averaged across subjects to create averaged T1- and T2*-maps on the cerebellar surface. T1 surfaces showed an alternation of lower and higher T1 values when going from the median to the lateral part of the cerebellar hemispheres. In addition, longer T1 values were observed in the more superficial gray matter layers. T2*-maps showed a similar longitudinal pattern, but no change related to the cortical depths. These patterns are possibly due to variations in the level of myelination, iron and zebrin protein expression.