A dendrite-resolved, in vivo transfer function from spike patterns to dendritic Ca 2+

Abstract Dendrites transform local electrical activity into intracellular Ca 2+ signals that drive plasticity 1,2 , yet the voltage→Ca 2+ mapping during natural behavior remains poorly defined. Here, we measure this transfer function via simultaneous voltage and Ca 2+ imaging throughout the dendritic arbors of hippocampal CA2 pyramidal neurons in behaving mice. Dendritic Ca 2+ exhibited a hierarchical activation pattern dominated by back-propagating action potentials: simple spikes primarily drove somatic and proximal Ca 2+ , whereas complex spikes produced larger somatic Ca 2+ signals and propagated farther into distal dendrites, sometimes in a branch-selective manner. Dendrite-restricted co-activation of voltage and Ca 2+ without concurrent somatic events was rare. A biophysics-inspired model accurately predicted local Ca 2+ transients from local voltage waveforms. Our data and model provide a quantitative understanding of when – and why – dendritic Ca 2+ signals in CA2 pyramidal cells arise during behavior.