A rodent. (credit: Carlos de Paz) Cerebellar granule cells, which make up the cerebellum, are the smallest and most abundant of all neuron types in the brain. These cells are known to contribute to motor function, attention, language, and fear. A recent study published in Nature demonstrates that these cells may also contribute to our expectations of whether a given action will result in a positive reward. It's a discovery that departs from our previous understanding of how these types of cells function. To examine the function of these cerebellar granule cells, the authors used a mouse model of reward and reward anticipation.