Changes in afferent input from macular receptors, produced by tilting the head with respect to gravity, can modulate discharge rates of neurons in all 4 major vestibular nuclei. All second-order vestibular neurons studied in a recent investigation are found to respond to tilting in opposite directions with rate changes of opposite sign. Complex responses, including all possible combinations of rate increases and decreases, are obtained from higher-order neurons. The largest responses to tilting are exhibited by second-order neurons in Deiters' nucleus and the descending nucleus, indicating that these neurons receive extensive input from macular afferent fibers. In agreement with the known patterns of reflex responses to tilting, the average discharge rate of vestibulospinal tract neurons, projecting to the cervicothoracic spinal cord, has been found to increase during tilt toward the ipsilateral side and decrease during tilt toward the opposite side, whereas the average discharge rate of neurons projecting to the lumbo-sacral spinal cord increased during tilt in both directions. Analysis of this data has shown that the difference in response between the two neuronal populations is related to the anatomical organization of Deiters' nucleus but has failed to reveal the significance of the large variability of responses evoked by the same tilt stimulus.
ASJC Scopus subject areas