Distal tuft dendrites shape and maintain new place fields.

Hippocampal pyramidal neurons support episodic memory by integrating complementary information streams into new 'place fields'. Distal tuft dendrites are thought to initiate place field formation via plateau potentials. However, the hitherto experimental inaccessibility of this dendritic compartment has rendered its in vivo function entirely unknown. We report that distal tuft dendrites are variably recruited during place field formation in mouse area CA1. This variability predicts place field information content and may account for the unique and unexplained association window underpinning place field formation. Surprisingly, tuft-associated plateau potentials primarily occur during subsequent place field traversals and may serve a maintenance function alongside robust local spatial tuning. Our findings represent a significant advance toward a mechanistic, subcellular understanding of memory formation in the hippocampus.