Research PaperOtoliths - Accelerometer and seismometer; Implications in Vestibular Evoked Myogenic Potential (VEMP)

- Mechanics theory for seismic instruments is applied to the otolith organs.
- Otoliths are accelerometers below the natural frequency and seismometers above.
- In seismometer mode the otoconial layer is at rest and the base is in motion.
- In seismometer mode otoliths report neuro-epithelial base displacement.
- High frequency Bone Conducted Vibration (BCV) results in striolar region stimulus.

Vestibular otolithic organs are recognized as transducers of head acceleration and they function as such up to their corner frequency or undamped natural frequency. It is well recognized that these organs respond to frequencies above their corner frequency up to the 2-3 kHz range (Curthoys et al., 2016). A mechanics model for the transduction of these organs is developed that predicts the response below the undamped natural frequency as an accelerometer and above that frequency as a seismometer. The model is converted to a transfer function using hair cell bundle deflection. Measured threshold acceleration stimuli are used along with threshold deflections for threshold transfer function values. These are compared to model predicted values, both below and above their undamped natural frequency. Threshold deflection values are adjusted to match the model transfer function. The resulting threshold deflection values were well within in measure threshold bundle deflection ranges. Vestibular Evoked Myogenic Potentials (VEMPs) today routinely uses stimulus frequencies of 500 and 1000 Hz, and otoliths have been established incontrovertibly by clinical and neural evidence as the stimulus source. The mechanism for stimulus at these frequencies above the undamped natural frequency of otoliths is presented where otoliths are utilizing a seismometer mode of response for VEMP transduction.