In vivo whole-cell recording from a medium ganglion (MG) cell. These cells exhibit frequent, small amplitude narrow spikes and infrequent, large broad spikes. The broad spikes propagate into the dendrites and serve as the trigger for inducing synaptic plasticity at parallel fiber synapses. Parallel fibers are the axons of the granule cell and convey a wide variety of signals including corollary discharge and proprioception.