As cartwheel cells exhibit spontaneous firing in vitro, at the beginning of the experiment, the resting membrane potential was adjusted to around −80 mV to suppress spontaneous firing by injecting a negative bias current (−50 to −150 pA). The amplitude of the bias current was kept constant throughout the experiment. Input resistance was measured by applying a small hyperpolarizing current pulse (−50 pA, 300-ms duration). For the measurement of action potential properties, simple or complex spikes were induced by brief, strong current injection (1-ms duration, 100-pA increment, up to 2500 pA). Threshold current was defined as the current amplitude that evoked action potential for the first time. The half-width of action potential was measured at the potential between the threshold and action potential peak. In complex-spiking neurons, the threshold potential, action potential amplitude, and the maximum rate of spike rise and decay of action potentials were calculated from the waveform of the first action potential. Statistical significance was tested using paired t tests; n.s.: not significant, *p < 0.05, **p < 0.01, ***p < 0.001.