Nyberg, Malte Nils Olof; (2024) Egocentric navigation-related representations in the rodent hippocampus. Doctoral thesis (Ph.D), UCL (University College London).

Text Nyberg_10195733_Thesis_corrections.pdf Access restricted to UCL open access staff until 1 March 2025. Download (118MB)

Abstract

The mammalian hippocampal formation contains several distinct populations of neurons involved in representing self-position and orientation. These neurons, which include place, grid, head direction, and boundary cells, are thought to collectively instantiate cognitive maps supporting flexible navigation. However, to flexibly navigate, it is necessary to also maintain internal representations of goal locations, such that goaldirected routes can be planned and executed. How the mammalian brain performs these functions is currently not known, although computational models and preliminary experimental results have suggested some candidate mechanisms (e.g., see: Nyberg et al. 2022). Here, we investigate this question by recording from principal pyramidal cells in the hippocampus (dorsal CA1) of rats while they perform a novel flexible and naturalistic navigation task. The navigation task was flexible in the sense that the rats were required to continuously make novel trajectories to a goal location, and natural in the sense that both the environmental layout and the goal location independently changed over time, mimicking real navigation scenarios. We specifically investigated whether hippocampal activity 1) became over-represented at the goal relative to other locations, or 2) exhibited distance and/or direction-tuning to the goal during navigation. Unlike some previous studies reporting increased hippocampal activity at the goal in stereotyped-navigation tasks (e.g., Dupret et al. 2010; Hollup et al. 2001b), we did not find evidence for such a mechanism in our flexible navigation task. Furthermore, unlike previous reports in bats that hippocampal cells can show tuning to a goal-vector (e.g., Sarel et al. 2017), we did not find strong evidence to support this claim. Specifically, we used a similar classification approach as Sarel et al. (2017) and found a minority of cells that became classified as having goal-distance and/or direction tuning. However, by incorporating a simulation approach, we discovered that this method had a high-false positive rate, that could explain most or all of our results. Furthermore, our classified cells were not, on average, more tuned to the goal relative to other locations in control analyses. In addition, we confirmed these results using a complementary modelling approach from Jercog et al. (2019), that finds the location in the environment that best accounts for the directional tuning of hippocampal cells. Our results suggest that during flexible navigation – which is presumed to critically engage hippocampal-dependent navigation and memoryrelated processes – there is no evidence for specific goal-tuning in hippocampal principal cells. Thus, goal representations and computations may take place elsewhere in the brain or, alternatively, in the hippocampus but in a more complex form that was either not directly investigated, or which can be readily read-out using electrophysiological approaches.

Download activity - last month

Export as CSVJSONXML

Download activity - last 12 months

Export as JSONCSVXML

Downloads by country - last 12 months

Export as XMLCSVJSON

Archive Staff Only

View Item