To date, all the electrophysiological methods for auditory testing rely on the measure on synchronous evoked auditory nerve activity. This measure only takes into account the response of the first action potential in every auditory fibber, but provides no information about the neural response during a sustained activity. This can explain why in experimental models, a loss of more of 80% of auditory nerve fibbers cannot be detected by usual electrophysiological measurements. In this study we aim at investigating the global spontaneous and sound evoked auditory nerve activity by recording directly the electrical field by an electrode placed directly on the auditory nerve of subjects during a skull base surgical procedure. We expected to demonstrated differences in the electrical activity between subjects with or without hearing loss.

Inclusion Criteria:

• 18 - 80 years ( inclusive borders)
• patient having to undergo surgery at the level of the ponto-cerebellar angle (microvascular decompression, vestibular neurotomy, tumor resection of the meningioma type or schwannoma) and
• Unaffected by neuro-sensory hearing loss, defined by mean auditory thresholds of less than 20 dB in tone audiometry in bone conduction on the side of the ear to be operated (N = 15, Group 1) or
• Showing mild to moderate hearing loss defined by average hearing loss (average of 500, 1000, 2000 and 4000 Hz thresholds) greater than 20 dB and less than 55 dB in air conduction threshold tone audiometry (N = 15 Group 2).
• Voluntary subjects to participate in the study,
• Subjects having signed written consent to participate in the study,
• Easily accessible topics.

Exclusion Criteria:

• Subjects unable to understand the nature and goals of the study and / or having difficulty communicating with the investigator,
• Subjects refusing to participate, subjects whose free and informed consent has not been sought, subjects for which a consent form has not been signed,
• Subjects for whom there is a contraindication to general anesthesia,
• Subjects with a central neurological pathology that can disrupt electrophysiological recordings
• Not affiliated to a French social security scheme or not benefiting from such a scheme,
• Majors protected by law,
• Pregnant women,
• deprived of liberty by judicial or administrative decision,
• Infectious or inflammatory pathology of the middle ear.