RESEARCH ARTICLE On the Firing Rate Dependency of the Phase Response Curve of Rat Purkinje Neurons In

Synchronous spiking during cerebellar tasks has been observed across Purkinje cells: how-ever, little is known about the intrinsic cellular mechanisms responsible for its initiation, cessation and stability. The Phase Response Curve (PRC), a simple input-output character-ization of single cells, can provide insights into individual and collective properties of neu-rons and networks, by quantifying the impact of an infinitesimal depolarizing current pulse on the time of occurrence of subsequent action potentials, while a neuron is firing tonically. Recently, the PRC theory applied to cerebellar Purkinje cells revealed that these behave as phase-independent integrators at low firing rates, and switch to a phase-dependent mode at high rates. Given the implications for computation and information processing in the cerebellum and the possible role of synchrony in the communication with its post-synaptic targets, we further explored the firing rate dependency of the PRC in Purkinje cells. We iso-lated key factors for the experimental estimation of the PRC and developed a closed-loop approach to reliably compute the PRC across diverse firing rates in the same cell. Our re-sults show unambiguously that the PRC of individual Purkinje cells is firing rate dependen