VESTIBULAR AFFERENT ACTIVITY AFTER CANAL PLUGGING

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DESCRIPTION: Plugging of reciprocal semicircular canal pairs eliminates the response associated with rotation about their associated axis at a frequency of 0.2 Hz. At higher frequencies, there is a Anormalization of the spatial responses of the angular vestibulo-ocular reflex (aVOR). The hypothesis of this study is that this normalization occurs because plugging does not eliminate the respons of the plugged canal. Rather, it modifies the canal dynamics so that the dominant time constant of the canal is lowered. At present, there is no direct evidence that plugged canal afferents respond to rotation at higher frequencies. Neither has central vestibular activity been studied following canal plugging to determine if indeed there is spatial adaptation. The purpose work will address the following questions: Does canal plugging modify the spatial and temporal characteristics of the afferents in response to rotation? How will the spatial characteristics of central vestibular neurons be affected by plugging of the lateral canals and by section of the lateral canal nerves? Vestibular afferents of the cynomolgus monkeys will be recorded before and after bilateral lateral canal plugging. It is expected that the amplitude of modulation of lateral-canal afferents will be approximately zero at 0.2 Hz after plugging, but will tend to Anormalize as the head oscillation frequency is increased up to 4.0 Hz. Vertical canal afferents should maintain their normal frequency characteristics. Spatial oculomotor and central vestibular neuronal responses will be compared following bilateral sectioning of the nerves and after canal plugging to determine whether there is significant spatial adaptation following nerve cut. It is expected that the spatial responses will be altered due to central adaptation, but that changes in spatial responses as a function of frequency will not be as significant as for canal plugging. This work should lead to a clearer understanding of how lesions, such as plugging and nerve section, affect the sensory processing of head movements and how the central vestibular system adapts to these types of lesions.