Retrosplenial PV and SST interneurons shape egocentric spatial precision and stability

Accurate navigation requires egocentric representations of environmental geometry to be continuously updated by self-motion while remaining stable over time. The retrosplenial cortex (RSC) is central to this process, yet how local inhibitory circuits support this balance remains unclear. We show that parvalbumin (PV) and somatostatin (SST) interneurons regulate distinct components of egocentric spatial coding in RSC. PV interneurons are strongly modulated by self-motion and exhibit bearing-aligned synchrony that precedes SST activation, linking movement to egocentric coding precision. In contrast, SST interneurons display weak self-motion modulation but robust boundary-anchored activity with globally coherent dynamics that stabilize representations over time. Optogenetic silencing revealed dissociable effects: PV perturbation degraded egocentric coding precision while SST perturbation disrupted global population organization. Behaviorally, PV silencing impaired initial egocentric orientation while SST silencing preserved initial orientation but impaired its sustained update. These findings identify separable inhibitory mechanisms balancing rapid updating with representational stability during navigation.