Fig. 4: LV2 correlations between IdC MPM measures and NODDI in white matter.

a The relative contributions of each NODDI metric to the overall pattern are calculated as a sum of the design scores and expressed as a percentage. Covariance of ODI with IdC integrity is the primary driver of this pattern. b The strength and direction of the relationship that each measure of isodendritic core microstructure (R1, MTsat, R2*, PD) has with the voxels highlighted in (c) for each measure of white matter microstructure (NDI, ODI or FW). Error bars show 95% confidence intervals from 1000 bootstrapped samples. The midpoint of each bar represents the correlation using the full dataset. Non-significant correlations (confidence intervals overlapping with zero) are faded out. c The yellow voxels indicate a positive relationship with the pattern shown in (b). The blue voxels indicate a negative relationship. Only voxels with a bootstrap ratio of >|2| are colored. These plots can be interpreted as follows: Greater R1 in LC is associated with lower NDI in yellow regions (brainstem efferent tracts) and greater NDI in blue regions (limbic tracts), as the correlation value in (b) is negative. Greater R1 in LC is also associated with greater ODI in yellow regions and lower ODI in blue regions, as the correlation value in (b) is positive. R1 in LC is not associated with FW in this pattern, as the correlation value confidence intervals in (b) overlap with zero. Overall, in this pattern, we see positive associations between R1, MTsat and R2* across all isodendritic core nuclei and ODI in yellow regions (brainstem efferent tracts) and negative associations with ODI in blue regions (limbic tracts). LC locus coeruleus, DR dorsal raphe, VTA ventral tegmental area, NbM nucleus basalis of Meynert, MTsat magnetization transfer saturation, PD proton density, NDI neurite density index, ODI orientation dispersion index, FW free water fraction. Source data are provided as a Source Data file.