NeuroImage
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Spinocerebellar ataxia type 17 (SCA17) is a rare autosomal dominant neurodegenerative disorder characterized by progressive cerebellar ataxia but also a broad spectrum of other neuropsychiatric signs. As anatomical and structural studies have shown severe cerebellar atrophy in SCA17 and a differentiation of the human cerebellum into an anterior sensorimotor and posterior cognitive/emotional partition has been implicated, we aimed at investigating functional connectivity patterns of two cerebellar clusters of atrophy revealed by a morphometric analysis in SCA17 patients. In particular, voxel-based morphometry (VBM) revealed a large cluster of atrophy in SCA17 in the bilateral anterior cerebellum (lobule V) and another one in the left posterior cerebellum (lobules IX, VIIb, VIIIA, VIIIB). ⋯ In turn, task-based task-independent functional connectivity analyses revealed that the cerebellar posterior seed was linked with fronto-temporo-parietal areas as well as partly the insula and the thalamus, i.e., brain regions implicated in cognitive and affective processes. Functional characterization of experiments activating either cerebellar seed further corroborated this notion, revealing mainly motor-related functions for the anterior cluster and predominantly cognitive functions were associated for the posterior one. The differential functional connectivity of the cerebellar anterior and posterior cluster highlights the manifold connections and dichotomy of the human cerebellum, providing additional valuable information about probably disrupted cerebellar-cerebral connections and reflecting the brunt of motor but also the broad spectrum of neuropsychiatric deficits in SCA17.
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Quantitative susceptibility mapping (QSM) is a novel magnetic resonance-based technique that determines tissue magnetic susceptibility from measurements of the magnetic field perturbation. Due to the ill-posed nature of this problem, regularization strategies are generally required to reduce streaking artifacts on the computed maps. ⋯ HEIDI resulted in susceptibility maps without streaking artifacts and excellent depiction of subtle susceptibility variations in most regions. By investigating HEIDI susceptibility maps acquired with the volunteers' heads in different orientations, it was demonstrated that the apparent magnetic susceptibility distribution of human brain tissue considerably depends on the direction of the main magnetic field.
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The first aim of the present study was to extend previous findings of similar cerebellar cortical areas being involved in verbal and spatial n-back working memory to the level of the cerebellar nuclei. The second aim was to investigate whether different areas of the cerebellar cortex and nuclei contribute to different working memory tasks (n-back vs. Sternberg tasks). ⋯ On the other hand, the focus of activation in right lobule VI in the verbal Sternberg task suggests specific cerebellar contributions to verbal working memory. The verbal Sternberg task emphasizes maintenance of stimuli via phonological rehearsal, whereas central executive demands prevail in n-back tasks. Based on the model of working memory by Baddeley and Hitch (1974), the present results show that different regions of the cerebellum support functions of the central executive system and one of the subsidiary systems, the phonological loop.
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One of the promises of Ultra High Field (UHF) MRI scanners is to bring finer spatial resolution in the human brain images due to an increased signal to noise ratio. However, at such field strengths, the spatial non-uniformity of the Radio Frequency (RF) transmit profiles challenges the applicability of most MRI sequences, where the signal and contrast levels strongly depend on the flip angle (FA) homogeneity. In particular, the MP-RAGE sequence, one of the most commonly employed 3D sequences to obtain T1-weighted anatomical images of the brain, is highly sensitive to these spatial variations. ⋯ Regarding the low-FA k(T)-point based excitations, the FA uniformity achieved at 7 T surpassed what is typically obtained at 3 T. Subsequently, automated white and gray matter segmentation not only confirmed the expected improvements in image quality, but also suggests that care should be taken to properly account for the strong local susceptibility effects near cranial cavities. Overall, these findings indicate that the k(T)-point-based pTx solution is an excellent candidate for UHF 3D imaging, where patient safety is a major concern due to the increase of specific absorption rates.
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Selective attention and multisensory integration are fundamental to perception, but little is known about whether, or under what circumstances, these processes interact to shape conscious awareness. Here, we used transcranial magnetic stimulation (TMS) to investigate the causal role of attention-related brain networks in multisensory integration between visual and auditory stimuli in the sound-induced flash illusion. ⋯ We found that disruption of the right angular gyrus, but not of the adjacent supramarginal gyrus or of a sensory control site, enhanced participants' veridical perception of the multisensory events, thereby reducing their susceptibility to the illusion. Our findings suggest that the same parietal networks that normally act to enhance perception of attended events also play a role in the binding of auditory and visual stimuli in the sound-induced flash illusion.