Fundamental and Clinical Study of Cochlear Synaptopathy

Not Applicable

Recruiting

Interventions: Procedure: near field recording of human auditory nerve activity during retro sigmoid approach with contact electrode

Brief Summary: In humans, surface electrophysiological recording of the cochlear nerve in response to a sound stimulus provides information about the integrity and function of synapses (synaptic transmission) and nerve fibre function. However, this information remains global. The investigators have preliminary data showing that it is possible to extract and characterise the functional properties of nerve fibres during otoneurosurgery in humans, and therefore to isolate the neuronal sub-populations mentioned above more precisely than is currently possible. The use of these electrophysiological data from near-field recordings, i.e. in contact with the nerve, will enable the design and improvement of a mathematical model of the human cochlea. This model will provide access to the individual responses of each nerve fibre and fill the current gap in knowledge between the functioning of these fibres and global surface recordings.

Detailed Description: During functional surgery on the cerebellopontine angle, a ball electrode is placed on the human cochlear nerve to monitor hearing. Once the electrode is in place, clicks and random noise bands will be delivered in order to analyze the cochlear electrophysiological signal produced. Depending on the characteristics recorded, this signal can be used at a given frequency and intensity to identify the populations of auditory neurons mainly involved. Prior to surgery, each patient will have been examined by the audiologist in order to determine the auditory thresholds in silence and noise, in tone and in speech, to carry out the digit test and to perform an electrocochleography and distortion products. Each result analyzed will be the subject of a further analysis using the mathematic model of the human cochlea.

Recruitment & Eligibility

Inclusion Criteria

Not provided

Exclusion Criteria

Not provided

Arm && Interventions

Group	Intervention	Description
normal hearing patients	near field recording of human auditory nerve activity during retro sigmoid approach with contact electrode	free of neuro-sensory deafness, defined by mean hearing thresholds of less than or equal to 20 dB HL in pure tone audiometry in air conduction bilaterally on the side of the ear operated on and on the non-operated side from 0.25 to 8 kHz
hearing impaired patients	near field recording of human auditory nerve activity during retro sigmoid approach with contact electrode	have a sensorineural hearing loss defined by hearing thresholds of 20 dB HL or better from 0.25 to 2 kHz and from 20 dB HL excluded to 55 dB HL at frequencies above 2 kHz.

Primary Outcome Measures

Name	Time	Method
Compare the amplitude and spectrum of global evoked auditory nerve activity with basic stimuli between patients defined as normo and hearing loss based on preoperative audiometric tests	At 48 months	During ponto cerebellum retro sigmoide surgeryelectrocochleography and distortion products.
In response to a stimulus, the neurophonic potential recorded in the form of a wave called PSTR will be characterised patients defined as normo and hearing loss based on preoperative audiometric tests	At 48 months	During ponto cerebellum retro sigmoide surgery. In response to a stimulus, the neurophonic potential recorded in the form of a wave called PSTR will be characterised patients defined as normo and hearing loss based on preoperative audiometric tests by the following indices:- the amplitude of the peak- the amplitude of the plateau- the peak to plateau ratio- the time constant for the rapid decay of the peak- the time constant for the slow decay of the peak.

Secondary Outcome Measures

Name	Time	Method
compare the primary objective with the results obtained with a mathematical model of the human cochlea in order to improve the responses of our model.	At 48 months	During ponto cerebellum retro sigmoide surgery