Event:

Frank Sengpiel (School of Biosciences, Cardiff University)

In rodents as well as in primates, the retrosplenial cortex (RSC) integrates inputs from the hippocampal formation with those from sensory areas, especially the visual cortex, and plays a key role in spatial memory and navigation. Until recently, little has been known about how the RSC processes visual information, and how visuospatial memories are encoded at neuronal population level.
We have shown that the dysgranular part of the RSC (RSCd) contains a retinotopic map of visual space. The activity of individual neurons is modulated by locomotion, both in darkness and in the presence of visual stimuli. The response to visual cues is stable over time, indicating an egocentric representation of visual space.
Using in vivo two-photon imaging, we have demonstrated the gradual emergence in RSCd of context-specific patterns of neuronal activity over a 3-week period, which are re-instated upon retrieval more than 3 weeks later. These spatial memory engrams become progressively more stable with learning and are maintained over several weeks. The degree of memory retention is related to the stability of the engrams, suggesting a possible mechanism for memory consolidation.
Using head-mounted miniscopes, we are investigating how familiar vs. novel locations are encoded in the RSC. In a radial-arm maze mice spend longer time exploring novel arms compared with familiar arms for delay times up to 30 minutes, and this is correlated with an overall increase in RSC activity in novel arms. However, there are two distinct population of neurons in the RSC, one responding preferentially in novel, the other in familiar locations. We are currently studying how placing the maze in darkness affects mouse behaviour as well as RSC activity. We are further analysing whether raising mice in complete darkness affects their spatial memory and the activity of RSC neurons.