Large endolymphatic potentials from low-frequency and infrasonic tones in the guinea pig

Abstract

Responses of the ear to low-frequency and infrasonic sounds have not been extensively studied. Understanding how the ear responds to low frequencies is increasingly important as environmental infrasounds are becoming more pervasive from sources such as wind turbines. This study shows endolymphatic potentials in the third cochlear turn from acoustic infrasound (5 Hz) are larger than from tones in the audible range (e.g., 50 and 500 Hz), in some cases with peak-to-peak amplitude greater than 20 mV. These large potentials were suppressed by higher-frequency tones and were rapidly abolished by perilymphatic injection of KCl at the cochlear apex, demonstrating their third-turn origins. Endolymphatic iso-potentials from 5 to 500 Hz were enhanced relative to perilymphatic potentials as frequency was lowered. Probe and infrasonic bias tones were used to study the origin of the enhanced potentials. Potentials were best explained as a saturating response summed with a sinusoidal voltage (Vo), that was phase delayed by an average of 60° relative to the biasing effects of the infrasound. Vo is thought to arise indirectly from hair cell activity, such as from strial potential changes caused by sustained current changes through the hair cells in each half cycle of the infrasound.

The Auditory Nerve Overlapped Waveform (ANOW) Originates in the Cochlear Apex

“…Note that pre-injection CR dif,mid (pCM) amplitudes from inside scala media were much larger than from the round window: mean scala media 50 dB SPL = 478±90 1 μV from 15 measurements in three ears (five pre-injection measures from three ears) and mean round window 50 dB SPL =16±3 μV from 20 measurements in four ears. The large scala media/round window difference is consistent with Salt et al (2013). The consistency during TTX administration of CR dif,mid (pCM) from inside the scala media (Fig.…”

“…The average of B and C yields a waveform that oscillates at twice the frequency (D). This result is caused by the asymmetry of the response waveforms, seen as more saturation at negative potentials compared to positive in B and C. Lower: E is a Boltzmann inputoutput function (for equations, see Salt et al 2013) with parameters derived from fitting the measured response.…”

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…No data for human subjects are available, but, considering the higher sensitivity of humans for LF sounds, similar results can be expected (Salt et al 2013). Hirsh and Ward (1952) observed temporary deteriorations of human absolute thresholds about 2 min after presenting subjects with an intense, non-traumatic LF tone.…”

“…sound with frequencies lower than 250 Hz (Berglund et al 1996), has been considered to largely bypass the inner ear even at intense levels, simply because human hearing thresholds for frequencies below 250 Hz are relatively high. Recent evidence from animal models shows that physiological cochlear responses to LF sound are even larger than those evoked by equallevel, higher frequencies in the more sensitive range of hearing (Salt et al 2013).…”

Amplitude modulation of audible sounds by non-audible sounds: Understanding the effects of wind turbine noise

“…Therefore, several simultaneous inputs from many outer hair cells are required for type II-fiber firing, suggesting that the most effective stimulus would be that which maximally excites a broad cochlear length. Large outer-haircell potentials and broad cochlear displacement in response to infrasound and low-frequencies within the range of audibility (Salt et al 2013) suggest that type II fibers would fire most efficiently by such stimuli. While type II firing may be subconscious if evoked by sound from wind turbines, type II fibers innervate a region of the central auditory nervous system that extends to innervate regions responsible for, among other things, regulating attention, arousal, and pain/stress (Salt & Kaltenbach 2011;Kaltenbach & Godfrey 2008;Benson & Brown 2004;Brown et al 1988).…”