Deep Cerebellar Nuclei Rebound Firing In Vivo: Much Ado About Almost Nothing?

How the output neurons of the cerebellum, the neurons of the deep cerebellar nuclei (DCN), encode information remains a matter of much debate. DCN neurons have the requisite biophysical characteristics to exhibit rebound firing and fire a brief but high-frequency burst of action potentials after pauses brought about by strong hyperpolarizations. Rebound firing is an attractive coding mechanism as it can provide a timed signal with a high signal-to-noise ratio to downstream motor areas. However, whether DCN rebound firing is a common signaling mechanism under physiological conditions remains to be demonstrated. We analyzed postpause firing rates of DCN neurons in awake animals in vivo under a number of behavioral conditions, including cerebellar-intensive behaviors such as balancing on a beam and walking on a treadmill. We did not find any evidence in support of a role for rebound firing in encoding information under any of these behavioral conditions.