For more than a century, studies have confirmed the involvement of the cerebellum in the control and coordination of ongoing movements 1, 2, 3, 4. In the last several years, however, research has revealed its substantial contribution to cognitive and emotional functions, thus prompting the revision of the more restricted view of the cerebellum as purely a motor structure 5, 6, 7. The recent discovery that many cell types in the cerebellum encode reward delivery, expectation, size, and omission — which are typically attributed to the basal ganglia — has elicited intense interest 8, 9•, 10, 11, 12, 13, 14. In addition, works have reported the existence of nonmotor cerebellar functions, including higher cognitive functions such as working memory, language, time representation and interval assessment 15, 16, 17, 18, and sleep-dependent memory processing [19], but also social preference 20, 21, 22•, fear learning and extinction 23, 24, 25, the regulation of defensive states [26], movement planning and vigor 27, 28, 29, emotional enhancement of episodic memory [30], and promotion of satiation [31]. The role of the cerebellum in the majority of these functions has been corroborated by clinical symptoms in cases of cerebellar dysfunction, such as ataxia, essential tremor, dyslexia, autism, and various psychiatric disorders, including bipolar disorder, post-traumatic stress disorder, attention deficit, and schizophrenia 32, 33, 34, 35, 36, 37, 38, 39, 40.

The discovery of these numerous cerebellar-dependent functions has been complemented by advances in understanding of the cerebellar anatomy and the variety of cellular and physiological mechanisms it exploits. The basic cerebellar circuit comprises a three-layered cortex that receives excitatory input from the mossy fibers (MFs) and climbing fibers (CFs), which in turn projects its output to the deep cerebellar nuclei (CbN) via the Purkinje cells (PCs) that constitute the sole output from the cerebellar cortex (CC). The CbN integrate inhibitory input primarily from the PCs and excitatory input from both the MF and the CF collaterals [41]. Overall, the cerebellum is considered to be a highly modular structure with many recurrent connections that support both feedforward and feedback information transfer and regulation [42].

For many decades, cerebellar research centered on the CC but sidelined the CbN that were assumed to simply be relay stations. Technological advances in research techniques and methodology have now demonstrated that there is more to CbN computation than meets the eye. This review sheds light on these newly discovered anatomical and physiological mechanisms that shape the activity of CbN neurons, and describes the key pathways that may enable the cerebellum to intervene rapidly and efficiently in a variety of brain functions.