Olivier Coulon: Morphological features of sulci and their relationship to function and connectivity
Channel: Brain Web
Date: 14/07/2021

Morphological features of sulci and their relationship to function and connectivity

Cortical folds, or sulci, are the main visible features when observing the cortex at a macroscopic scale and, as such, they are often used to define locations on the surface of the cortex and, to some extent, describe macroscopic cortical organization. The current presentation will describe how sulcal morphology can be used to define functionally relevant landmarks within specific folds.

Starting with the central sulcus (CS), I will first define the sulcal profile, a morphological curve that quantifies the antero-posterior variations in shape of the CS along its dorso-ventral axis. The sulcal profile of the CS can be used to locate automatically the well-known hand-knob, a morphological landmark in the CS that has been associated with the primary motor area of the hand(1). Functional data will be presented that show a strong relationship between the location of this motor area and that of features extracted from the sulcal profile(2). Sulcal depth is another feature that has been used to characterize cortical shape, and it will be demonstrated that variations in sulcal depth can be used to describe morphology and localize function. Specifically, evidence will be provided for how inter-hemispheric depth asymmetries within the superior temporal sulcus (STS) can be used to localize temporal voice areas(3), that is, functional areas that respond specifically to vocal sounds.

Studies have shown strong relationships between morphology and function at the group level, but sulcal patterns show topological and geometrical variations that often make it difficult to establish inter-subject correspondences. Therefore, the group average is not representative of individual sulcal morphology. It has been proposed that morphological features called ‘annectant gyri’ or ‘plis-de-passage’ (PdP) can explain inter-individual variations in sulcal patterns(4). Studies will be presented that suggest that PdPs are related to specific short-range U-shape white matter connectivity(5,6). More specifically, PdPs appear to occur at the location of a denser connectivity between the two opposite banks of a sulcus, which in some cases might explain the link between specific PdPs and functional areas(7).

To conclude, the above research demonstrates the value of studying morphological features of sulci. Despite the existence of inter-subject variability in sulcal patterns, morphological features, such as sulcal depth, can provide insight into the functional organization of the cerebral cortex and its local short-range white matter connectivity.

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2. Coulon, O. et al. (2011). Two new stable anatomical landmarks on the central sulcus: Definition, automatic detection, and their relationship with primary motor functions of the hand, in IEEE EMBC 2011, pp.7795-7798, Boston, USA.
3. Bodin, C. et al. (2018). Anatomo-functional correspondence in the superior temporal sulcus. Brain Structure and Function, 223, 221-232.
4. Ochiai, T. et al. (2004). Sulcal pattern and morphology of the superior temporal sulcus. NeuroImage, 22, 706-719.
5. Pron, A. et al. (2020). U-shape short-range extrinsic connectivity organisation around the human central sulcus. Brain Structure and Function. doi:10.1007/s00429-020-02177-5
6. Bodin, C. et al. (2020). Plis de passage in the superior temporal sulcus: Morphology and local connectivity. NeuroImage, 117513. doi:10.1016/j.neuroimage.2020.117513
7. Boling, W. et al. (1999). Localization of hand motor activation in Broca’s pli de passage moyen. Journal of Neurosurgery, 91, 903-910.