The inferior olive transforms upstream sensorimotor errors into cerebellar teaching signals

Summary Adaptive behavior requires evaluating whether sensory feedback matches expectations derived from motor commands. In cerebellar theories, climbing fibers arising from the inferior olive (IO) convey prediction error signals that instruct learning, yet how these signals are constructed remains unresolved. Using larval zebrafish performing visuomotor behaviors in virtual reality, we combined two-photon calcium imaging with glutamate sensors to measure excitatory input to the IO and climbing fiber output under identical conditions. IO activity scaled with discrepancies between expected and experienced optic flow across open- and closed-loop perturbations. Strikingly, excitatory drive to the IO already contained structured, motor-dependent information consistent with error-like signals. Comparison of input and output revealed selective, frequency-dependent transmission from the olive to the cerebellum. These findings suggest where error representations arise in the olivo-cerebellar pathway and support a model in which climbing fiber teaching signals reflect upstream processing combined with filtering within the IO.