Is the cerebellum like cerebellar-like structures?

The cerebellum and cerebellar-like structures (including the dorsal and medial octavolateral nucleus of fishes and amphibians, the electrosensory lateral line lobe of electroreceptive teleost fishes and the dorsal cochlear nucleus of mammals) have similar anatomy, common developmental origins and common cellular markers. Transplanted embryonic Purkinje cells integrate into cerebellar-like structures but not neighboring brain parenchyma, and mutations that cause cerebellar degeneration cause similar defects in cerebellar-like structures. This review advances the idea that these neuroanatomical and molecular similarities have functional equivalents. The main structural difference between the cerebellum and cerebellar-like structures, the inferior olivary nucleus, can be viewed as a relay station that evolution has interposed along the path of flow of primary sensory information to the cerebellum. Gating of sensory information to the cerebellum occurs at the level of inferior olivary nucleus depending on whether arriving information is expected. Activation of inferior olivary neurons leads to plasticity, and finely tuned inhibitory inputs suppress olivary excitation when the plasticity is not needed. Functionally, the olivo-cerebellar system performs the same kind of computation as cerebellar-like structures: the subtraction of sensory expectations.