The present investigation is dedicated to elucidating how head movements are encoded in the discharge characteristics of primary afferent neurons innervating the semicircular canal cristae of the vestibular labyrinth. Its additional objective is to show how this neural code is distributed within the cerebellar cortex. The experiments are designed to determine how dynamic response characteristics, as reflected in broad-band systems transfer functions and in a novel approach to characterizing vestibular afferent receptive fields, are distributed with respect to the entire afferent ensemble. A morphophysiology strategy will show how these systems response characteristics are mapped onto the peripheral crista neuroepithelium. Experiments are also designed to determine how afferent spatial and temporal coding is reflected in the projections of vestibular afferent mossy fibers to the ventral uvula and nodulus of the cerebellar cortex. The results from these studies will elucidate the foundation of sensory coding in the semicircular canal afferent system, and the bases to interpret the contribution of afferent physiologic diversity to processing within the cerebellum. The ensuing maps will also provide the bridge between investigations of the peripheral receptor and the functional coding in the afferent neurons, which will provide a functional context with which to interpret studies of hair cell physiology and pathophysiologic investigations of peripheral vestibular lesions. The experiments to be conducted in this investigation utilize electrophysiologic recording and intracellular labeling methods in a mammalian model to identify the features of sensory coding that are associated with specific morphologic and physiologic characteristics of the afferent neuron. Extensive electrophysiologic recordings will be conducted to elucidate the continuum of afferent response dynamics among the afferent ensemble. These are analyzed in the context of a model of receptive fields for these neurons, in which individual afferents code for a region of head-movement state space. Afferent response dynamics are investigated with respect to the locus of innervation within the crista, and with respect to their terminations within the cerebellar uvula and nodulus. These experiments will reveal new insight regarding the fundamental organization of stimulus coding in this sensory system.
