Electrophysiological assessment of temporal envelope processing in cochlear implant users

Area of Science:

• Neuroscience
• Biomedical Engineering
• Audiology

Background:

• Cochlear implant (CI) users require accurate encoding of temporal envelope modulations (TEMs) for speech comprehension.
• Clinical success in CI users is linked to the fidelity of neural ensemble encoding of TEMs.
• Non-invasive electroencephalography (EEG) could offer a method to assess this encoding, but is challenged by large stimulation artifacts.

Purpose of the Study:

• To develop and validate an EEG method for artifact-free measurement of neural responses to electrical stimulation in CI users.
• To assess the feasibility of using EEG measures to evaluate the encoding of temporal envelope modulations (TEMs) in CI users.
• To compare the sensitivity of the 40-Hz electrically evoked auditory steady-state response (eASSR) and electrically evoked auditory change complex (eACC) to modulation depth.

Main Methods:

• Utilized a custom-built, high-sample-rate EEG system to precisely capture stimulation artifacts.
• Employed linear interpolation to remove artifacts, enabling the isolation of neural responses.
• Measured 40-Hz eASSR and eACC in ten adult CI users using amplitude-modulated pulse trains at various modulation depths.

Main Results:

• Successfully recorded artifact-free 40-Hz eASSRs and eACCs in CI users.
• Demonstrated that the 40-Hz eASSR exhibited significant responses even at shallow modulation depths.
• Observed that the eACC was less responsive at shallower modulation depths compared to the 40-Hz eASSR.

Conclusions:

• The 40-Hz eASSR is a robust and artifact-free measure of neural encoding in CI users.
• The 40-Hz eASSR shows potential as a clinically viable objective tool for assessing TEM encoding.
• This method could aid clinicians in optimizing CI performance by identifying and potentially disabling non-responsive electrodes.