Isabel Muzzio, Ph.D.
Biotechnology, Sciences, and Engineering
University of Texas
“Neural codes of reorientation”
Reorientation – regaining one’s bearings after becoming lost – is a fundamental problem of navigation. During disorientation, the internal sense of direction is unreliable and lost navigators must reorient only using external cues. Of all the external cues available to reorient, geometry has been shown to play a predominant role across species, even when other directionally informative cues, such as landmarks, are present. However, the ability to reorient is affected by age. While the hippocampal map of young mice aligns to the geometry of the layout during reorientation, the cognitive map of old lost animals displays instability. These previous studies were conducted in situations without contextual ambiguity, more recently we studied what happens when lost animals do not recognize their surroundings. In this scenario animals must recover their facing direction within a context (heading retrieval) and simultaneously recognize where they are (context recognition), two processes that we hypothesized would require the use of geometric and non-geometric features, respectively. To test this idea, we trained disoriented mice to locate rewards in two chambers with identical geometry, distinguishable based on the visual features along one wall, while we recorded hippocampal neuronal activity. We observed that although visual features were used to identify the chambers, those very same cues were not used to disambiguate facing direction within a chamber. Rather, recovery of heading retrieval relied exclusively on the use of geometry. At the neuronal level, cells discriminated context identity using a rate code and facing direction using a location code. These data suggest that context recognition and heading retrieval are independent cognitive processes that are differentially represented in the brain during reorientation.