Neuronal competition shapes the encoding, consolidation, and retrieval of precise spatial memories in mice

Memories are encoded in sparse neuronal ensembles called engrams, but whether core engram principles generalize from simple associative learning to complex, integrative memories remains unclear. Using a spatial foraging task in mice, we show that, as in conditioned fear, competitive activity-dependent allocation governs the formation of dorsal CA1 hippocampal engrams supporting precise, multifaceted spatial information. Silencing these ensembles impaired retrieval, whereas optogenetic reactivation restored spatial memory even under cue-degraded conditions. We further show that memories encoded in close temporal proximity link through overlapping ensembles via excitability-dependent allocation. Finally, artificial reactivation of a spatial engram was sufficient to drive appropriate behavior in ambiguous contexts. These findings identify neuronal competition as a fundamental organizing principle of engram formation and memory linking, showing that hippocampal engrams encode the detailed information required for adaptive navigation through mechanisms shared with simpler associative paradigms.