Fig. 1. Microstructural gradients in the striatum revealed in vivo.

(A) Automatic computation of the putamen’s AP axis in a single subject and calculation of a microstructural gradient along it. (B and C) R1 gradients along three axes of the left putamen (B) and caudate (C) in 23 young adults (dataset A). The typical spatial change between segments is represented by the fixed effect β, estimated using a mixed-effects model for each axis. The sign of β denotes a positive or negative gradient, i.e., an increase or decrease in R1 (s⁻¹) along the axis. (In subsequent analyses, cases of a nonlinear change along the axis are approximated using two linear models. See Methods and table S1.) P values are FDR-corrected. (D) The R1 functions along axes of a control white matter (WM) region show almost no change, ruling out image bias as an explanation for the measured striatum gradients. (E and F) Replications in two independent datasets (datasets B and C) in 3T (E) and 7T (F). The agreement between datasets is shown in each panel using linear regression between the average R1 functions along the putamen AP axis and along the caudate ML axis. Insets: R1 spatial functions from dataset A (gray) and dataset B or C (color). Data in (F) are z-scored since different strength fields yield different R1 ranges. Shaded areas and error bars represent ±1 SD.