Simple spikes occur at rates of 17 - 150 Hz (Raman and Bean, 1999), either spontaneously or when Purkinje cells are activated synaptically by the parallel fibers, the axons of the granule cells.
Complex spikes are slow, 1-3 Hz spikes, characterized by an initial prolonged large-amplitude spike, followed by a high-frequency burst of smaller-amplitude action potentials.