We describe with a variant of the Golgi method a new type of neuron that is 
prominently represented in the granular layer of the mammalian 
vestibulocerebellum but is presently neglected in all major accounts on the 
cerebellum. These neurons, here termed unipolar brush cells, are intermediate in 
size between granule cells and Golgi cells. They typically have a thin and 
presumably myelinated axon, and a single and stubby dendrite whose tip forms a 
tightly packed group of branchlets resembling a paintbrush. The branchlets often 
intertwine with the digitiform claws of granule cell dendrites and are 
occasionally approached by Golgi cell dendrites, indicating that the unipolar 
brush cells may share the input of the other granular layer neurons. Branchlets 
of neighboring unipolar brush cells converging into the same neuropil island 
also occur. The brush-like tip of the unipolar cell engulfs one or two mossy 
fiber rosettes to form an extensive synapse that appears to close recurrent 
loops involving the vestibular nuclei. Positive feedback in these loops could 
help to explain several motor responses and drive mechanisms of extended 
duration that are controlled by the ventral cerebellum.