Study of the Fine Structure and Temporal Envelope of the Human Cochlea in Response to Human Vocalizations

The Functional Role of Cochlear Synaptopathy for Speech Coding in the Brain

In humans, surface electrophysiological recordings of the cochlear nerve in response to a sound stimulus provide information about the cochlear's ability to encode sound. Depending on the stimulus, the fine structure and temporal envelope of the signal will vary, allowing us to determine its characteristics. By phenotyping patients before surgery using subjective and objective audiometric tests, it will be possible to isolate for each patient the moment when the fine structure disappears and when the temporal envelope is effective.

During functional cerebellopontine angle surgery, a spherical electrode is placed on the human cochlear nerve to monitor hearing. Once the electrode is in place, clicks and speech signals with and without noise are delivered to analyze the cochlear electrophysiological signal produced. Depending on the characteristics recorded, this signal can be used to determine how fine structure and temporal envelope are encoded by the cochlea. Prior to surgery, each patient is evaluated by an audiologist to determine quiet and noise thresholds, tone and speech, electrocochleography, distortion testing, tympanometry, ABR and psychoacoustic testing.

Inclusion criteria:

• The following will be included as hearing-impaired patients:

  • Male or female
  • Over 18 and up to 80 years of age
  • Normal otoscopic examination
  • Scheduled for surgery on the cerebellopontine angle (microvascular decompression)
  • With sensorineural hearing loss defined by average hearing thresholds between 21 dB HL and 40 dB HL at 0.5, 1, 2 and 4 kHz
  • Affiliated to a social security scheme
  • Having read the information note describing the study and having agreed in writing to participate by signing the informed consent form

• Will be included as normal-hearing patients:

  • Male or female
  • Over 18 and up to 80 years of age
  • Normal otoscopic examination
  • Scheduled for surgery on the cerebellopontine angle (microvascular decompression)
  • Free of sensorineural hearing loss, defined by average hearing thresholds of less than or equal to 20 dB HL in tonal air conduction audiometry, bilaterally on the side of the ear undergoing surgery and on the side not undergoing surgery, at 0.5, 1, 2 and 4 kHz
  • Affiliated to a social security scheme
  • Having read the information note describing the study and having agreed in writing to participate by signing the informed consent form

Exclusion criteria: patients will be excluded from the study if the auditory nerve is not accessible during surgery:

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