Topographic and somatotopic organization of functional connectivity between the intraparietal sulcus and primary somatosensory cortex in macaque monkeys

The research examined the intricate relationship between the intraparietal sulcus (IPS) and four distinct regions of the primary somatosensory cortex (S1) in 10 awake rhesus macaques, utilizing resting-state functional magnetic resonance imaging (fMRI). The goal was to understand the fine-scale topographic organization between these brain regions.

Across the S1 subregions and both hemispheres, the researchers observed a highly structured spatial organization of IPS-S1 connectivity. This organization followed a systematic pattern characterized by anteroposterior and mediolateral gradients, forming a semi-oval topology that mirrored the geometry of the intraparietal sulcus.

The connectivity between the IPS and S1 regions exhibited stronger connections towards the cortical banks and convexities, while weaker connections were found near the sulcal fundus. This pattern could not be attributed to reduced local temporal signal-to-noise ratio.

Employing unsupervised hierarchical clustering, the researchers identified connectivity-defined subdivisions that, while distinct, only partially align with classical cytoarchitectonic boundaries. Along the S1 mediolateral axis, significant troughs in cluster-averaged connectivity profiles corresponded to previously identified somatotopic transitions. These transitions delineated boundaries between tongue and face representations, as well as between hand and trunk-leg representations.

These findings suggest that the functional organization of the IPS is shaped by a complex interplay of large-scale sulcal topology and the fine-grained organization of S1 subregions and body-part representations. This dual influence contributes to the functional specialization of individual IPS regions.