Spatial and Temporal Characteristics of Vestibular Convergence

In all species studied, afferents from semicircular canals and otolith organs converge on central neurons in the brainstem. However, the spatial and temporal relationships between converging inputs and how these contribute to vestibular behaviors is not well understood. In the current study, we used discrete rotational and translational motion stimuli to characterize canal- and otolith-driven response components of convergent non-eye movement (NEM) neurons in the vestibular nuclear complex of alert pigeons. When compared to afferent responses, convergent canal signals had similar gain and phase ranges but exhibited greater spatial variability in their axes of preferred rotation. Convergent otolith signals also had similar mean gain and phase values to the afferent population but were spatially well-matched with the corresponding canal signals, cell-by-cell. However, neither response component alone nor a simple linear combination of these components was sufficient to predict actual net responses during combined canal-otolith stimulation. We discuss these findings in the context of previous studies of pigeon vestibular behaviors, and we compare our findings to similar studies in other species.