Fig. 3.

Efferent action on afferent discharge. (A–C) Activation of the efferent vestibular system by delivering 200 shocks per second to the brainstem (30) typically increased the average discharge rate (spk/s) of sensitive afferents and reduced the peak-to-peak amplitude of modulation. For sinusoidal stimuli greater than ∼2-μm indentation (equivalent to ∼8°/s angular head rotation), efferent activation had no obvious effect on displacement of the cupula (e.g., B). (D and E) Continuous activation of the efferent system evoked tonic changes in afferent discharge rates far outlasting transient discharge modulations induced by mechanical stimuli (*). Subsequent results shown in Figs. 4 and 5 report changes in cupula motion during tonic efferent activation.