A utricular origin of frequency tuning to low-frequency vibration in the human vestibular system?

Recent work has demonstrated that the human vestibular system displays a remarkable sensitivity to low-frequency vibration. To address the origin of this sensitivity we compared the frequency response properties of vestibular reflexes to 10ms bursts of air-conducted sound and transmastoid vibration, which are thought to be differentially selective for the saccule and utricle, respectively. Measurements were made using two separate central pathways: vestibular evoked myogenic potentials (VEMPs), which are a manifestation of vestibulo-collic projections, and ocular vestibular evoked myogenic potentials (OVEMPs), which are a manifestation of vestibulo-ocular projections. For both response pathways air-conducted sound and vibration stimuli produced the same patterns of quite different tuning. Sound was characterised by a band-pass tuning with best frequency between 400 and 800Hz whereas vibration showed a low-pass type response with a largest response at 100Hz. Our results suggest that the tuning is at least in part due to properties of end-organs themselves, while the 100Hz best frequency may be a specifically utricular feature.