Processing reliant on granule cells is essential for motor learning but dispensable for many cerebellar-dependent behaviors

Cerebellar dysfunction leads to motor, learning, emotional, and social deficits. It is assumed that these deficits arise from impaired processing of mossy fiber inputs that activate granule cells (GCs) that in turn excite Purkinje cells (PCs). However, high-frequency spontaneous PC firing might also influence behaviors. To clarify how the cerebellum regulates behaviors, we compared the effects of disrupting either GC signaling, which selectively perturbs cerebellar processing, or PC signaling, which disrupts cerebellar processing and spontaneous PC firing. We find that both GC and PC signaling are required for eyeblink conditioning and vestibulo-ocular reflex (VOR) learning. However, disrupting PC signaling impairs baseline VOR, anxiety, and social behaviors, but abolishing GC signaling does not. This establishes that cerebellar processing is essential for motor learning, but is not required for many cerebellum-dependent behaviors. This suggests that such behaviors could be rescued by elevating firing in downstream targets, as shown previously for social deficits.