Uncoupling of dysgranular retrosplenial “head direction” cells from the global head direction network
Spatial cognition is an important model system with which to investigate how sensory signals are transformed into cognitive representations. Head direction cells, found in several cortical and subcortical regions, fire when an animal faces a given direction and express a global directional signal which is anchored by visual landmarks and underlies the \"sense of direction\". We investigated the interface between visual and spatial cortical brain regions and report the discovery that a population of neurons in the dysgranular retrosplenial cortex, which we co-recorded with classic head direction cells in a rotationally symmetrical two-compartment environment, were dominated by a local visually defined reference frame and could be decoupled from the main head direction signal. A second population showed rotationally symmetric activity within a single sub-compartment suggestive of an acquired interaction with the head direction cells. These observations reveal an unexpected incoherence within the head direction system, and suggest that dysgranular retrosplenial cortex may mediate between visual landmarks and the multimodal sense of direction. Importantly, it appears that this interface supports a bi-directional exchange of information, which could explain how it is that landmarks can inform the direction sense while at the same time, the direction sense can be used to interpret landmarks.