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All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. Insertion of cochlear implant (CI) Electrode Array
NOTE: The intracochlear electrode array consists of four platinum bands (Ø0.2 mm) with platinum/iridium parylene insulated wire shielded in a silicone tube (Figure 1).
- Place the retractor tool in the incision to re-access the bulla.
- Insert the electrode array into the round window (scala tympani) at a depth where the 4th platinum ring is located just inside the round window. This gives an insertion depth of ~2 mm, corresponding to an intracochlear position at ~30 kHz.
- Coil the lead wire inside the bulla and glue the wire to the tissue above the bulla. Coiling the wire helps to keep the array in place throughout the experiment.
- Carefully remove the retractor and close the insertion with tissue glue.
- Make a small incision (0.5 mm) in the neck perpendicular to the line between where the active and reference auditory brainstem response (ABR) electrodes will be using a tissue scissor. Place the platinum ground ball in the subcutaneous pocket and close the small incision with tissue glue (Figure 2).
- Connect the electrode array board to the Animal Stimulator Platform (ASP).
2. Electric Auditory Brainstem Response (eABR)
NOTE: An Animal Stimulator Platform is used to electrically stimulate the electrode array. Other current sources and software systems can be used.
- Clean the ABR electrodes with 70% ethanol solution. Place the electrodes under the skin: active (Ch1) on the vertex, reference (-) below the pinna of the ipsilateral ear, and ground in the hind leg (Figure 2).
- Open the ASP software and define the electric pulse stimulation paradigm. We use a charge-balanced biphasic pulse with 50 μs/phase and 10 μs interphase gap presented at 23.3 pulses per second (pps). The electric stimulation is delivered in a monopolar electrode configuration with increasing current levels. A total of 400 responses are averaged at each current level.
- Present the electric pulse trains and record the evoked eABR response continuously via the Tucker Davis Technologies (TDT) headstage, pre-amplifier, and auditory processor.
- Plot and analyze the eABR data via a custom-made Matlab script (Figure 3). The script and an example of a recording are provided in the Supplementary.
