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Trial Lecture – time and place
See Trial Lecture.
Adjudication committee
- First opponent: Professor Tobias Rose, Bonn University, Germany
- Second opponent: Associate Professor Tora Bonnevie, Norwegian University of Science and Technology - NTNU,
- Third member and chair of the evaluation committee: Associate Professor Andreas Lossius, University of Oslo
Chair of the Defence
Professor Farrukh Abbas Chaudhry, University of Oslo
Principal Supervisor
Associate Professor Koen Gerard Alois Vervaeke, Oslo University
Summary
Space, time, and objects form the framework within which we experience our daily lives. Importantly, episodic memories – which are essential for learning and planning – rely on a spatial context, the specific objects involved, and their sequence in time. While the hippocampus is traditionally seen as the center for spatial navigation and memory, the retrosplenial cortex (RSC) is emerging as another crucial player. In this thesis, I provide new insights into the distributed networks and cellular mechanisms involved in these processes, emphasizing the retrosplenial cortex (RSC) as a crucial hub.
In the first study, we investigated the origin of position tuning in the RSC. We used two-photon Ca2+ imaging to analyze long-range inputs to the RSC during navigation. We found that most long-range axons to agranular RSC convey position information, with the secondary motor (M2) and posterior parietal cortex (PPC) providing the most spatial information. These findings demonstrate that the RSC participates in a brain network that shares position information.
In the second study, we aimed to understand the role of the RSC in integrating tactile input for navigation and memory. Mice navigated a tactile virtual reality environment while we used two-photon Ca2+ imaging. We discovered RSC neurons that encode object location within a spatial map. These signals often anticipate and maintain a memory of the object's position even when absent, suggesting the RSC creates a dynamic spatial representation integrating tactile data.
In the third study, we examined how gain modulation shapes spatial representations. Using optogenetics and mice navigating a linear track, we found that activating vasoactive intestinal peptide (VIP) expressing interneurons in the RSC selectively enhanced the response intensity of position-tuned cells. Hippocampal place cells were only minimally affected. Simulations revealed this area-specific gain modulation mechanism is beneficial for the RSC's weaker spatial signals but would be less advantageous to already sharp hippocampal maps.
And in the last study we explored how the brain represents time in the neocortex. Mice were trained to remember odors for specific durations. Imaging revealed area- specific differences. The RSC demonstrated sequential firing patterns encoding both odor and time, while this was less prominent in neighboring areas (including posterior parietal, visual, somatosensory, and motor cortices). This highlights the important role of the RSC in episodic memory and supports the idea of distributed time encoding.
These studies collectively highlight the RSC's role in spatial navigation and memory formation. They demonstrate how the RSC integrates diverse position signals, incorporates tactile information, and participates in temporal coding for episodic memories. Furthermore, the identification of a VIP-mediated gain modulation mechanism in the RSC provides insights into cellular processes that optimize spatial representations in the brain. These findings advance our understanding of the complex neural networks that allow us to navigate our world and remember our experiences.
Additional information
Contact the research support staff.