The Computational Functions of the Inferior Olive: Clues from Evolution

Precerebellar structures, mainly studied in weakly electric fish, act to remove the effects of the fish's own movements on the electrical signals they receive, but do not directly control movement, nor do they have a clear error signal. The cerebellum does directly control movement - arguably the most prominent difference in function between the two structures. The most pronounced anatomical difference between precerebellar structures and the cerebellum itself is that the latter possesses an inferior olive. This conjunction suggests that the inferior olive carries out a function that is necessary for the control of movements. What is the crucial function that the inferior olive carries out? Summary A clue comes from the the example of the vestibulo-ocular reflex. Allowing image movement degrades the visual signal irretrievably. It is therefore necessary to issue movement commands to prevent image movement, as in the vestibular-ocular reflex. But then the output of the precerebellar system is no longer an estimate of the actual sensory signal and can no longer serve as an error signal. This problem appears to have been addressed by the evolution of the inferior olive, which does provide an error signal. The inferior olive thus allows the cerebellum to participate in the control of movements. We consider evidence about how this works in practice. The evidence supports the view that the computational function of the inferior olive is indeed to provide an error signal for the control of movement.