Hearing mechanisms:
The auditory system is divided into 3 parts. The outer ear consists of the external ear (the pinna) and the ear canal. The middle ear is a cavity between the eardrum and the inner ear. It is air-filled and is connected to the back of the throat by the eustachian tube, which opens during swallowing and yawning and allows air to enter the middle ear, thus enabling the pressure in the middle ear to be maintained. The inner ear consists of the cochlea and the vestibular labyrinth. The latter is part of the systems controlling the balance mechanisms of the body.

Sound waves are transmitted by the eardrum through the middle ear as vibrations, which in turn are amplified by a series of small bones, attached to the eardrum at one end and to the oval window of the inner ear at the other. The sound waves are converted to electrical impulses by specialized cells in the cochlea, the outer hair cell (OHC). The impulses are then transmitted to the auditory cortex of the brain in the temporal lobe by the auditory nerve (cranial nerve 8).

The OHC generates sounds (emissions) because the cells have spontaneous motility, that causes backward energy propagation from the cochlea to the middle ear, and then to the ear canal, where they can be recorded using a special microphone. These emissions are called otoacoustic emissions (OAE). A special type is distortion product otoacoustic emissions (DPOAE), which are evoked by stimulation with two pure tones of different frequencies.

Aran and colleagues (2004) studied the effect on the ear mechanisms of exposing guinea pigs to RFR at 900 MHz frequency (SAR 1, 2 or 4 W/kg). They found no evidence of any damage to the inner ear or the auditory pathways. Galloni (2005) found no effect of 900 MHz RFR on the cochlear cells of rats. Galloni's group also failed to find evidence that 900 or 1800 MHz RFR affects the inner auditory system of rats. Parazzini (2007) reported no effect of RFR exposure (900 MHz frequency at 4 W/kg, 2h/d, 5 days a week, for 4 weeks) ± gentamicin on the auditory system of rats.

Authors
Aran JM, Carrere N, Chalan Y, Dulou PE, et al. (2004):
Title
Effects of exposure of the ear to GSM microwaves: in vivo and in vitro experimental studies.
Journal
Int J Audiol 43:545-54.
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Authors
Galloni P, Lovisolo GA, Mancini S, Parazzini M, et al. (2005):
Title
Effects of 900 MHz electromagnetic fields exposure on cochlear cells functionality in rats: Evaluation of distortion product otoacoustic emissions.
Journal
Bioelectromagnetics 26:536-547.
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Authors
Galloni P, Parazzini M, Piscitelli M, Pinto R, et al. (2005):
Title
Electromagnetic fields from mobile phones do not affect the inner auditory system of Sprague-Dawley rats.
Journal
Radiat Res 164:798-804.
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Authors
Parazzini M, Galloni P, Piscitelli M, Pinto R et al. (2007):
Title
Possible combined effects of 900 MHz continuous-wave electromagnetic fields and gentamicin on the auditory system of rats. 
Journal
Radiation Research 167:600-605.
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