Time-slicing: a model for cerebellar function based on synchronization, reverberation, and time windows

We present a new theory of cerebellar function that is based on synchronization, delayed reverberation, and time windows for triggering spikes. We show that granule cells admit messy fiber activity to the parallel fibers only if the Golgi cells are firing synchronously and if the spikes arrive within short and well-defined time windows. The time window mechanism organizes neuronal activity in discrete 'time slices' that can be used to discern meaningful information from background noise. In particular, Purkinje cell activity can trigger rebound spikes in deep cerebellar nuclei cells which project via brain stem nuclei and messy fibers back to the cerebellar cortex. Large network simulations reveal that a form of synaptic plasticity at the parallel fiber/Purkinje cell synapses that relies on the timing of parallel and climbing fiber spikes allows the system to learn, store, and recall spatio-temporal patterns of spike activity. The present theory sheds new light on several experimental observations such as the high degree of climbing fiber spike synchrony, the width of micro zones, and developmental changes in inhibitory postsynaptic currents of granule cells.