The fine evaluation of the function of auditory neurons in silence and in noise in humans is difficult, if not impossible, to date with the conventional methods available. That is why in certain situations, the hearing aids of patient with hearing loss fail, especially in the presence of noise.

In this study the investigators aim at investigating the global spontaneous and sound evoked human auditory nerve activity from electrophysiological acquisitions performed directly on the cochlear nerve in patients requiring posterior fossa surgery.

The fine evaluation of the function of auditory neurons in silence and in noise in humans is difficult, if not impossible, to date with the conventional methods available. That is why in certain situations, the hearing aids of patient with hearing loss fail, especially in the presence of noise.

In this study the investigators aim at investigating the global spontaneous and sound evoked human auditory nerve activity from electrophysiological acquisitions performed directly on the cochlear nerve in patients requiring posterior fossa surgery.

Stimulations will be performed in silence and in noise from stimuli identical to those used during the preoperative auditory assessment: clic and speech syllable stimulation. These acquisitions will allow us to compare clinical and electrophysiological data in order to better understand the coding of hearing in normal and hearing loss humans under silent and noisy conditions. A prospective longitudinal study will be performed.

inclusion criteria :

Will be included as hearing impaired patients:

• male or female
• over 18 years of age
• who are to undergo surgery on the cerebellopontine angle (microvascular decompression, vestibular neurotomy, removal of a meningioma or schwannoma tumor)
• with a mild to severe sensorineural hearing loss defined by an average hearing loss (average of thresholds obtained at 500, 1000, 2000 and 4000 Hz) greater than 20 dB and less than 90 dB in pure tone bone conduction audiometry on the side of the operated ear.
• affiliated to a social security system.
• have read the information note describing the study and have agreed in writing to participate by signing the informed consent form.

Will be included as normal hearing patients:

• male or female
• over 18 years of age
• who are to undergo surgery in the cerebellopontine angle (microvascular decompression, vestibular neurotomy, removal of a meningioma or schwannoma tumor)
• free of neuro-sensory deafness, defined by average hearing thresholds less than or equal to 20 dB in tonal bone conduction audiometry on the side of the operated ear
• affiliated with a social security system.
• having read the information note describing the study and having agreed in writing to participate by signing the informed consent form.

exclusion criteria :

Patients for whom the auditory nerve is not accessible during surgery,

• because of a complete tumor invasion of the cochlear nerve (stage III and IV neuroma, advanced meningioma)
• because of an anatomical feature not identified during the preoperative examination, making its exposure for recordings impossible (protrusion of the posterior face of the rock)