Fig. 2: Ultra-high angular resolution postmortem diffusion MRI allows us to (a) characterise the diffusion signal in great detail, (b) find more tertiary populations and estimate fibre orientations with increased precision, (c) reconstruct longer streamlines and increase inter-hemispheric connectivity, particularly to the occipital and temporal lobe, and (d) reconstruct the SLF II with increased confidence.

a Each point represents the diffusion signal along a single gradient direction. The voxel is shown from two orthogonal views. b The Ball and Stick model was fitted to data with varying angular resolution. Both the number of fibre populations, and the precision of the orientation estimates is plotted. Boxplot interpretation: box limits indicate upper and lower quartiles, whilst whiskers indicate the range of data not considered as outliers. The white matter mask included 30061 voxels for the b = 4 ms/μm² and 30690 voxels for b = 7 or 10 ms/μm² data. c Comparing connectivity matrices from 64 and 1000 gradient datasets. Since the difference matrix is symmetric, the bottom half is used to highlight interesting features: the green box indicates interhemispheric connectivity, with the turquoise box showing connections between parietal and premotor areas; the dark blue boxes show intrahemispheric connectivity of areas that are separated along the inferior-superior axis. Streamlines whose length <10 mm are considered `short', 10–50 mm are `mid' length and >50 mm are `long'. d Reconstruction of the superior longitudinal fasciculus (SLF) II using probabilistic tractography.