Simple spikes and complex spikes

Abstract

Cerebellar Purkinje neurons communicate with downstream circuit elements by generating two distinct types of electrical activity. Purkinje neurons fi re conventional action potentials, termed simple spikes, and they also intermittently fi re a highly stereotyped burst of decrementing spikes, called a complex spike. Each of these types of electrical activity arises from an interaction between synaptic input and distinct excitability mechanisms intrinsic to Purkinje neurons. Simple spikes occur at very high frequencies in the range of 50 spikes per second and are driven by pacemaking ion channels expressed by Purkinje neurons. This high simple spike rate is then modulated by excitatory and inhibitory synaptic input. Complex spikes occur in response to excitatory synaptic input from the climbing fi ber; these compound electrical events are driven in part by the large voltage-gated calcium conductance in the dendrites of Purkinje neurons. Finally, the two forms of excitability interact; complex spikes can exert indirect effects on simple spike fi ring rate. Together, these two fi ring behaviors endow Purkinje neurons with a range of signaling behaviors critical for cerebellar contributions to motor coordination and motor learning.