Regaining our bearings: Neural representations and circuits underlying spatial reorientation.

Isabel Muzzio

University of Texas San Antonio

https://utsa.zoom.us/j/92387759081

Friday, February 18, 2022

11 AM – 12 PM CST

Reorientation – regaining one’s bearings after becoming lost – is a fundamental navigation process wherein the internal sense of direction becomes unreliable, forcing disoriented navigators to reorient only using external cues. Across species the geometry of the surrounding space plays a dominant role in reorientation, even when other directionally informative cues, such as landmarks, are available. Consequently, the modular theory has proposed that reorientation is driven by a mechanism that is sensitive to geometry and impermeant to non-geometric landmarks. In support of this theory, we have shown that the hippocampal map aligns to the geometry of a layout during reorientation. However, the modular theory’s exclusive reliance on geometry fails in situations of contextual ambiguity (identity of a context is unclear) as well as following overtraining, after animals learn the directional value of landmarks and use these cue to minimize errors in geometrically equivalent locations. In these situations, disoriented animals must identify the environment in which they are lost (context recognition) and recover facing direction within the context (heading retrieval). Disoriented animals initially use non-geometric landmarks to perform context recognition, but exclusively rely on the shape of the layout to compute heading retrieval; however, over time they incorporate features to recover heading in order to maximize reward. The neural mechanisms associated with these processes exhibit unique patterns of activity and dynamics. Following disorientation, heading retrieval cells rapidly align to environmental geometry, while context recognition cells align to local landmarks over days, as animals learn the value of these cues. We further demonstarte that the retrosplenial cortex (RSC), a region involved in scene perception containing neurons responsive to location, borders, and head-direction, is required for the use of geometry during reorientation. These inputs are modulated by a long-range GABAergic projection from CA1 to RSC, which inhibits the use of geometry, thereby enhancing the use of landmarks, as animals learn their directional value. This research uncovers important aspects of navigation with critical applications to the fields of robotics and health.