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The vestibular nerve sends signals to the brain that code the movement and position of the head in space. These signals are used for a variety of functions, including the control of reflex and voluntary movements and the construction of a sense of self-motion. In order to carry out these functions, sensory vestibular signals need to be transformed in a variety of ways. Transformations are thought to occur at an early stage of sensory processing in the brain, and in many cases are apparent in the responses of neurons in the vestibular nuclei that receive direct inputs from the vestibular nerve. Several specific examples of sensory transformation in the vestibular nuclei are presented, and current hypotheses about the mechanisms that are used to produce the transformations are discussed.

The contributions of vestibular nerve afferents and central vestibular pathways to the angular (AVOR) and linear (LVOR) vestibulo-ocular reflex were studied in squirrel monkeys during fixation of near and far targets. Irregular vestibular afferents did not appear to be necessary for the LVOR, since when they were selectively silenced with galvanic currents the LVOR was essentially unaffected during both far- and near-target viewing. The linear translation signals generated by secondary AVOR neurons in the vestibular nuclei were, on average, in phase with head velocity, inversely related to viewing distance, and were nearly as strong as AVOR-related signals. We suggest that spatial-temporal transformation of linear head translation signals to angular eye velocity commands is accomplished primarily by the addition of viewing distance multiplied, centrally integrated, otolith regular afferent signals to angular VOR pathways.

Neurons in the vestibular nuclei and the prepositus nucleus exhibited several different types of changes in their firing behavior during voluntary cancellation of the horizontal VOR. The head velocity sensitivity of type I position-vestibular-pause neurons was reduced during cancellation, while type II vestibular neurons exhibit an increase in their sensitivity. The firing behavior of burst tonic neurons in the medial vestibular nucleus, the prepositus nucleus, like the cells in the abducens nucleus, was closely related to the eye movements generated when the VOR is cancelled. Other cells in the PH and MVN respond primarily to smooth pursuit eye movements. We suggest that the behavior of abducens neurons during the VOR and during VOR cancellation can be explained if they receive inputs from PVP neurons, burst tonic neurons, and smooth pursuit neurons.