Updating the sulcal landscape of the human lateral parieto-occipital junction provides anatomical, functional, and cognitive insights

Abstract

Recent work has uncovered relationships between evolutionarily new small and shallow cerebral indentations, or sulci, and human behavior. Yet, this relationship remains unexplored in the lateral parietal cortex (LPC) and the lateral parieto-occipital junction (LPOJ). After defining thousands of sulci in a young adult cohort, we revised the previous LPC/LPOJ sulcal landscape to include four previously overlooked, small, shallow, and variable sulci. One of these sulci (ventral supralateral occipital sulcus, slocs-v) is present in nearly every hemisphere and is morphologically, architecturally, and functionally dissociable from neighboring sulci. A data-driven, model-based approach, relating sulcal depth to behavior further revealed that the morphology of only a subset of LPC/LPOJ sulci, including the slocs-v, is related to performance on a spatial orientation task. Our findings build on classic neuroanatomical theories and identify new neuroanatomical targets for future "precision imaging" studies exploring the relationship among brain structure, brain function, and cognitive abilities in individual participants.

Keywords: Cortical folding; Functional neuroanatomy; Magnetic resonance imaging (MRI); Occipital cortex; Parietal cortex; Spatial orientation.

Fig. 1.. Four previously undefined small and shallow sulci in the lateral parieto-occipital junction (LPOJ).

a. Four example inflated (top) and pial (bottom) left hemisphere cortical surfaces displaying the 13–17 sulci manually identified in the present study. Each hemisphere contains 1–4 of the previously undefined and variable LOC/LPOJ sulci (slocs and pAngs). Each sulcus is numbered according to the legend. b. Criteria for defining slocs and pAngs components. (i) Slocs-v is the cortical indentation between the cSTS3 and lTOS. (ii) Slocs-d is the indentation between cSTS3/cSTS2 and IPS-PO. (iii) pAngs-v is the indentation between the cSTS2 and pips. (iv) pAngs-d is the indentation between cSTS2/cSTS1 and IPS. c. The variability of the slocs and pAng components can cause them to disappear when individual surfaces are averaged together. Left to right: (i) 10 HCP participants, (ii) 20 HCP participants, (iii) 100 HCP participants, and iv) 650 HCP participants. The disappearance of these sulci on average surfaces, which are often used for group analyses in neuroimaging research, emphasizes the importance of defining these structures in individual hemispheres.

Fig. 2.. The slocs-v is morphologically, architecturally, and functionally dissociable from nearby sulci.

a. Radial plot displaying the morphological (upper metrics: depth, surface area) and architectural (lower metrics: cortical thickness, myelination) features of the slocs-v (gray), cSTS3 (blue), and lTOS (green). Each dot and solid line represents the mean. The dashed lines indicate ± standard error. These features are colored by sulcus (legend). Metrics are in standardized units. b. Radial plot displaying the connectivity fingerprints of these three sulci: the Dice Coefficient overlap (values from 0–1) between each component and individual-level functional connectivity parcellations (Kong et al., 2019).

Fig. 3.. The morphology of LPC/LPOJ sulci, including the slocs-v, is related to cognitive performance.

a. Beta-coefficients for each left hemisphere LPC/LPOJ sulcus at a range of shrinking parameter values [alpha (α)]. Highlighted gray bar indicates coefficients at the chosen α-level. Bottom: Cross-validated mean-squared error (MSE_CV) at each α level. By convention, we selected the α that minimized the MSE_CV (dotted line). b. Inflated left hemisphere cortical surface from an example participant highlighting the two groups of sulci—dorsal positive (orange) and ventral negative (green)—related to spatial orientation performance. c. Spearman’s correlation (r_s) between the measured and the predicted spatial orientation scores from the LASSO-selected model is shown in a.

Fig. 4.. The slocs-v relative to modern functional and cytoarchitectonic parcellations in LPC/LPOJ.

a. Top: Left (LH) and right (RH) hemispheres of the inflated fsaverage surface with two areas from the modern HCP multimodal parcellation (HCP-MMP; blue) (Glasser et al., 2016) relative to an MPM of the slocs-v (warm colors indicate areas with at least 20% overlap across participants; Supplementary Fig. 6). Bottom: Same as top, except for two observer-independent cytoarchitectonic regions from the Julich-Brain Atlas (Amunts et al., 2020). b. Overlap between the slocs-v and each area (Methods). Each dot and solid line represents the mean. The dashed lines indicate ± standard error (left: gray; right: white).

Fig. 5.. The slocs-v relative to retinotopy.

a. Top: Left (LH) and right (RH) hemispheres of the inflated fsaverage surface displaying the probabilistic locations of retinotopic maps from over 50 individuals from Wang and colleagues (L. Wang et al., 2015) (black outlines). The predicted slocs-v location from the MPMs is overlaid in orange (as in Fig. 4). (i), (ii), and (iii) point out the retinotopic maps in the cortical expanse spanning the TOS, IPS-PO, and IPS, respectively. b. Same format as in a, but with a map of the mean R² metric from the HCP retinotopy dataset (Benson et al., 2018) overlayed on the fsaverage surfaces (thresholded between R² values of 10% and 90%). This metric measures how well the fMRI time series at each vertex is explained by a population receptive field (pRF) model. The mean and max R² values for the slocs-v MPM in each hemisphere are included below each surface.