Taiping Zeng^1,3 (), Ming Bo Cai^2,3; ¹Fudan University, ²University of Miami, ³University of Tokyo

The representation of geometric structures of one's surroundings is key to self-localization during human spatial navigation. However, the spatial organization of geometry representation in the visual system has not been fully characterized. We displayed navigational videos from identical realistic virtual environments under different weather and lighting conditions to different participants while their brain activities are recorded by fMRI. By modeling the synchronized brain activity from participants watching videos of navigating through the same trajectories, we found that a compact representation of egocentric 3D scene geometric structures is present in a widespread network of brain regions. These regions carrying geometry-related signals form three parallel pathways, which we collectively refer to as "geometry visual pathways", starting from the primary visual cortex: the dorsal and medial pathways end in the intraparietal areas, while the ventral pathway arrives at the hippocampus via the parahippocampal gyrus. The synchronized neural activity in the identified geometry visual pathways allows for reliable decoding of the 3D scene geometric structures. Furthermore, road types, a more abstract representation of the route geometry, are encoded in overlapping pathways, distinctly absent from early visual cortex (V1, V2, V3). In addition to complementing the classical “what” and “where” dichotomy, the identified brain-wide geometry visual pathways narrow a critical gap in understanding how the brain constructs cognitive maps from visual inputs.

Acknowledgements: The study was funded by WPI-IRCN startup budgets (M.B. Cai and T. Zeng) and JSPS KAKENHI Grant Number JP21K20679 (T. Zeng). The research does not reflect the funders' opinions.