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https://elifesciences.org/articles/48932

Journal Club 9: Mapping the human subcortical auditory system using histology, postmortem MRI and in vivo MRI at 7T Main Question: How can current MRI capabilities used for the analysis of the subcortical auditory system answer remaining questions about the human auditory system. Methods: ● In vivo MRI. Functional MRI data were acquired with a 2-D Multi-Band Echo Planar Imaging (2D-MBEPI) sequence. ● Postmortem MRI. A human brainstem and thalamus specimen were dissected at autopsy from a 65-year-old anonymous male. MRI was acquired postmortem. Conclusions: ● It was found that the current methods for localizing the subcortical auditory pathway are effective. ● Atlases were derived from each localization method which will facilitate further investigations into the structure, function, and connectivity of the human subcortical auditory system in vivo. ● 3-D representations were made to benefit the learning of the human subcortical auditory pathway. Findings: ● The streamlines were constrained to only those that pass through auditory structures, and the connectivity map of the subcortical auditory pathway was visualized. It was observed that connectivity closely resembled the expected pattern of the human subcortical auditory wiring. Figure 3 shows the percentage of total streamlines connecting each of the subcortical auditory structures as estimated from the postmortem diffusion MRI sample. ● T2-weighted GRE imaging is sensitive to blood vessels, so they processed their anatomical MR image to highlight brainstem vasculature, which is shown in Figure 5. The 3-D vasculature images have a strong resemblance to post mortem data acquired with a stereoscopic microscope after full clearing method. ● Visual inspection and comparison to the MNI dataset showed that the MGB and IC could be identified on the basis of the anatomical contrast in their participants. However, while the SOC could be identified in the MNI dataset, it could not be identified in average anatomical image from 7T data. This data is shown in Figure 5. ● Figure 5 also shows the overlap of functional responses across participants, plotted on top of in vivo anatomical MRI, histology, and post mortem MRI. ● Figure 4 shows the statistically thresholded activation maps together with leave-one-out

probabilistic functional maps obtained considering all other individuals. ● Table 1 shows a quantification of the volume of functionally defined structures for different thresholds of the probabilistic group map. ● Table 2 shows the overlap between functional regions and the BigBrain segmentations after projection in MNI space. Further directions/ questions: The continued research and investigation of the subcortical auditory structures will allow future investigations of more complex human auditory processing....