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. In this model, mice are trained to push a lever to receive a small treat of sugar-water.

When the authors looked directly at the electrical activity in the brains of these mice, they saw that some of these cerebellar granule neurons were activated throughout the lever-pushing task. The peak of neuronal activity coincided with the peak of physical activity for up to 20 percent of the cells. However, not all populations of cells fired during the same part of the lever-pushing task, so the researchers wanted to learn more about the neuronal differences among these subpopulations of cells.