Direct and indirect parieto-medial temporal pathways for spatial navigation in humans: evidence from resting-state functional connectivity

Anatomical and functional findings in primates suggest the existence of a dedicated parieto-medial temporal pathway for spatial navigation, consisting of both direct and indirect projections from the caudal inferior parietal lobe (cIPL) to the hippocampus and the parahippocampal cortex, with indirect projections relaying through the posterior cingulate and retrosplenial cortex. This neural network is largely unexplored in humans. This study aimed at testing the existence of a parieto-medial temporal pathway for spatial navigation in humans. We explored the cortical connectivity patterns of the parahippocampal place area (PPA), the retrosplenial cortex (RSC), and the hippocampus (HC) using resting-state functional connectivity MRI. Our results demonstrate the existence of connections between the medial temporal lobe structures, i.e., PPA and HC, and the angular gyrus (AG), the human homologue of cIPL, as well as between RSC and AG. These connectivity patterns seem to reflect the direct and the indirect projections found in primates from cIPL to the medial temporal lobe. Such a result deserves feasible considerations to better understand the brain networks underpinning human spatial navigation.