Genetically eliminating Purkinje neuron GABAergic neurotransmission increases their response gain to vestibular motion.

Purkinje neurons in the caudal cerebellar vermis combine semicircular canal and otolith signals to segregate linear and gravitational acceleration, evidence for how the cerebellum creates internal models of body motion. However, it is not known which cerebellar circuit connections are necessary to perform this computation. We first showed that this computation is evolutionarily conserved and represented across multiple lobules of the rodent vermis. Then we tested whether Purkinje neuron GABAergic output is required for accurately differentiating linear and gravitational movements through a conditional genetic silencing approach. By using extracellular recordings from lobules VI through X in awake mice, we show that silencing Purkinje neuron output significantly alters their baseline simple spike variability. Moreover, the cerebellum of genetically manipulated mice continues to distinguish linear from gravitational acceleration, suggesting that the underlying computations remain intact. However, response gain is significantly increased in the mutant mice over littermate controls. Altogether, these data argue that Purkinje neuron feedback regulates gain control within the cerebellar circuit.