Distinct CA3 inputs differentially shape the learning-dependent evolution of right CA1 spatial maps

Spatial maps in hippocampal CA1 arise from place fields that support memory and navigation, yet how upstream inputs shape these maps during learning remains unclear. Here we show that CA3 projections from the left and right hemispheres make distinct contributions to right CA1 spatial representations as animals become familiar with a new environment. Using two-photon calcium imaging and optogenetic inhibition in mice navigating virtual tracks, we monitored and perturbed CA3 inputs converging onto CA1. CA1 spatial maps were initially inaccurate but stabilized within ~10 laps, marking a transition from an early learning phase to a later stable phase. During early learning, right-origin CA3 inputs exerted stronger influence on the refinement of spatial coding, whereas left-origin inputs became more important for maintaining stable representations later. Axonal recordings revealed a corresponding shift in spatial activity between right and left CA3 inputs over time. Together, these results reveal that distinct CA3 inputs dynamically redistribute their influence during learning to coordinate the refinement and stabilization of right CA1 spatial maps. Neural mechanisms underlying spatial dynamics across distinct memory phases are not fully understood. Here authors show that distinct inputs from the left and right CA3 dynamically shape CA1 spatial maps, shifting their influence from early refinement to later stability as animals learn a new environment.