Fig. 3: Identified structural connections reflect key features of thalamocortical circuit anatomy.
a, The C–Mt gradient derived in prior work20 maps spatial variation in the relative distribution of different thalamic projection cell types. This gradient, defined and visualized within the thalamus, spans from areas with the highest relative proportion of core-like thalamic projection neurons (yellow voxels; lower C–Mt values) to areas with the highest proportion of matrix-like neurons (dark purple voxels; highest C–Mt values). C–Mt values range from −0.3 to 0.2. b, Thalamocortical connections were each assigned a C–Mt value, indexing their position in the C–M gradient, based on where their streamlines terminated within the thalamus. Connection-specific C–Mt values are plotted in PNC and HCPD. C–Mt values were nearly perfectly correlated between datasets, confirming that delineated pathways terminated in the same areas of the thalamus across datasets. c, Thalamic connection C–Mt values positively correlated with the S–A axis rank of the connection’s cortical partner in both PNC (left) and HCPD (right). Both datasets showed evidence of core-to-sensory and matrix-to-association thalamocortical connectivity motifs. The positive linear relationship between S–A axis ranks and C–Mt values is plotted with a 95% confidence interval. d, Thalamocortical connections are shown colored by mean FA (dark yellow—highest FA; dark purple—lowest FA). FA values range from 0.2 to 0.5 across connections. e, FA values are plotted for all thalamocortical connections in PNC and HCPD. FA robustly correlated between datasets, demonstrating that this microstructural connectivity measure exhibits highly reproducible variability across thalamic pathways. f, Thalamocortical connection FA values monotonically decreased along the S–A axis in PNC (left) and HCPD (right), revealing a continuum of connection strength and coherence that exhibits systematic hierarchical variation. The negative linear relationship between S–A axis ranks and FA is plotted with a 95% confidence interval. In b, c, e and f, Spearman’s correlations were used to calculate r values, and the significance of the correlation was determined using conservative spin-based spatial rotation tests.
