THE FORMATION AND RETRIEVAL OF AN ABSTRACT COGNITIVE MAP IN HIPPOCAMPAL CA1

The hippocampus is a key brain region critical for the cognitive map – an internal representation of external environment for flexible spatial navigation. However, how hippocampal cells encode the ordinal relationship (abstract cognitive map), and how this encoding is gradually established through experience-dependent learning, remains largely unclear. Here, we developed a local cue-guided sequential spatial navigation task in which mice learned to visit maze arms following a specific sequence (A-B-C-D-A) guided by multisensory local cues. Using calcium imaging in dorsal hippocampal CA1 during the task, we discovered that neural population activity formed ring-shaped manifolds that emerged gradually during learning and represented the abstract sequential relationships between maze arms. Remarkably, when local cues were removed or swapped, both individual arm-selective neurons and population-level ring structures maintained their representations supporting the pattern completion. These findings reveal that hippocampal CA1 cells form an abstract cognitive map of ordinal sequences that can be retrieved to support flexible navigation by a pattern completion mechanism when environmental cues are degraded or changed.