Representation of visual landmarks in retrosplenial cortex

The process by which visual information is incorporated into the brain’s
spatial framework to represent landmarks is poorly understood. Studies in
humans and rodents suggest that retrosplenial cortex (RSC) plays a key
role in these computations. We developed an RSC-dependent behavioral task
in which head-fixed mice learned the spatial relationship between visual
landmark cues and hidden reward locations. Two-photon imaging revealed
that these cues served as dominant reference points for most task-active
neurons and anchored the spatial code in RSC. Presenting the same
environment but decoupled from mouse behavior degraded encoding fidelity.
Analyzing visual and motor responses showed that landmark codes were the
result of supralinear integration. Surprisingly, V1 axons recorded in RSC
showed similar receptive fields. However, they were less modulated by task
engagement, indicating that landmark representations in RSC are the result
of local computations. Our data provide cellular- and network-level
insight into how RSC represents landmarks.