Unipolar brush cells (UBCs) are glutamatergic neurons in the cerebellar cortex. Their morphology includes a brush-like dendrite, soma, and axon with large ‘mossy fiber’ terminals. They are classified as being excited or inhibited by glutamate (ON and OFF). UBCs may contribute to auditory and vestibular circuits whose dysfunction may lead to tinnitus and ataxia, respectively. This study explores UBC physiology, connectivity in cerebellar circuits, and contributions to circuit dysfunction.