Structural and functional evidence for ephaptic control of Purkinje cell spike timing by networks of molecular layer interneurons

Axon collaterals of type 1 molecular layer interneurons (MLI1s) contribute to pinceaux that engulf the initial segments of Purkinje cell (PC) axons and generate extracellular signals that ephaptically inhibit PCs. Here we show that a remarkably large number of MLI1s (~50) contribute to each pinceau, and that this allows networks of synchronously firing MLI1s to use ephaptic signals to control the precise timing of PC firing in vivo.