Entorhinal-retrosplenial circuits for allocentric-egocentric transformation of boundary coding

Spatial navigation requires landmark coding from two perspectives, relying
on viewpoint-invariant and self-referenced representations. The brain
encodes information within each reference frame, but their interactions
and functional dependency remains unclear. Here we investigate the
relationship between neurons in rat retrosplenial cortex (RSC) and
entorhinal cortex (MEC) that increase firing near boundaries of space.
Border cells in RSC specifically encode walls, but not objects, and are
sensitive to the animal’s direction to nearby borders. These egocentric
representations are generated independent of visual or whisker sensation,
but depend on inputs from MEC that contains allocentric spatial cells.
Pharmaco- and optogenetic inhibition of MEC cells led to a disruption of
border coding in RSC, but not vice versa, indicating
allocentric-to-egocentric transformation. Finally, RSC border cells fire
prospective to the animal’s next motion, unlike those in MEC, revealing
the MEC-RSC pathway as an extended border coding circuit that implements
coordinate transformation to guide navigation behavior.