Visual landmark coding and dynamic coupling with path integration circuits in area 29e of the rodent parahippocampal...

The brain relies on external landmarks to anchor internal spatial representations. The neural mechanisms underlying this process and the sources of landmark signals remain unknown in mammals. Here, we simultaneously recorded single neurons across five parahippocampal regions in rats navigating a virtual reality environment that preserved natural locomotion. Area 29e, an understudied parahippocampal field, displayed strong locking to visual landmarks under conditions in which neurons in the other regions, such as the medial entorhinal cortex, decoupled their spatial firing from the landmarks. Compared to the other regions, area 29e neurons also displayed weaker theta modulation, stronger gamma rhythmicity, stronger egocentric head-direction tuning, and enhanced landmark contrast sensitivity. The loss of landmark anchoring in non-29e parahippocampal neurons was preceded by a decline of gamma-band influence from 29e to medial entorhinal cortex. Together, these findings position 29e as a specialized visuospatial hub that may carry landmark signals for anchoring parahippocampal representations of space to the external world.