Direct cerebellar control over motor production in a species with extreme cerebellar enlargement

The cerebellum is thought to fine-tune movement without being required for its production. However, this textbook view derives mainly from studies of mammalian species with highly developed cerebral cortices. Here, we examined cerebellar function in the elephant-nose fish, a member of a family of African weakly electric fish (Mormyridae) in which the cerebellum is massively enlarged, covering the entire dorsal surface of the brain.^1,2,3,4,5 Although the microcircuitry and anatomical connections of the mormyrid "gigantocerebellum" have been well characterized, its function(s) remains unknown.^{6,7,8,9,10,11} The elephant-nose fish is named for a flexible facial appendage, the schnauzenorgan (SO), used to probe surfaces and extract prey from substrate.^8,12 Here, we provide evidence from microstimulation, electrophysiological recordings, and lesions for a direct and essential role for the C1 region of the mormyrid cerebellum in the production of SO movement. These findings indicate that the cerebellum may be capable of performing a wider range of functions than previously thought, including roles typically ascribed to the forebrain, and emphasize the importance of evolutionary history on the functional specialization of brain regions.