Frequency modulation of afferent and efferent unit activity in the vestibular nerve by oculomotor impulses.

Publisher Summary In this chapter, single unit activity is recorded from the peripheral vestibular nerve of unrelaxed and unanaesthetized goldfish, and rabbits. Eye movements are also registered. Nearly 10 % of the neurones show a frequency modulation starting before the beginning of each spontaneous saccadic eye movement and rapid phase of optokinetic and vestibular nystagmus. Bidirectionally activated (type-a) and bidirectionally inhibited (type-i) neurones can be established. In the goldfish, a few direction-specific neurones with inhibition or activation depending upon the direction of horizontal saccadic eyemovements (type-d) are found. The presaccadic initiated phasic discharge-modulation is supposed to originate from supranuclear optomotor centers. In addition to these phasically modulated neurons, found in both the goldfish and rabbit, the goldfish shows neurones whose discharge-frequency depends upon eye position (type-p). These neurones may be influenced by proprioceptive afferents from the eye muscle. Mainly in the goldfish, most of the neurones are identified as being efferent ones. In the rabbit, afferent bidirectionally activated neurones of type-a are verified. The results demonstrate the existence of a vestibular control by oculomotor impulses mediated by efferent fibers to the vestibular receptor level in teleosts and lower mammals. The possible functional significance is discussed in this chapter.