کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6287070 | 1615565 | 2016 | 12 صفحه PDF | دانلود رایگان |
- Electrically evoked auditory-steady state responses can be measured free from stimulation artifacts when stimulating with clinically relevant monopolar pulse rates in cochlear implant users.
- Modulation frequencies within the 30-50Â Hz region elicit prominent responses in adult cochlear implant users.
- Reduced synchronized activity is observed in adult cochlear implant users for electrically evoked auditory steady-state responses that originate at the brain stem.
Previous studies have shown that objective measures based on stimulation with low-rate pulse trains fail to predict the threshold levels of cochlear implant (CI) users for high-rate pulse trains, as used in clinical devices. Electrically evoked auditory steady-state responses (EASSRs) can be elicited by modulated high-rate pulse trains, and can potentially be used to objectively determine threshold levels of CI users. The responsiveness of the auditory pathway of profoundly hearing-impaired CI users to modulation frequencies is, however, not known. In the present study we investigated the responsiveness of the auditory pathway of CI users to a monopolar 500 pulses per second (pps) pulse train modulated between 1 and 100Â Hz. EASSRs to forty-three modulation frequencies, elicited at the subject's maximum comfort level, were recorded by means of electroencephalography. Stimulation artifacts were removed by a linear interpolation between a pre- and post-stimulus sample (i.e., blanking). The phase delay across modulation frequencies was used to differentiate between the neural response and a possible residual stimulation artifact after blanking. Stimulation artifacts were longer than the inter-pulse interval of the 500Â pps pulse train for recording electrodes ipsilateral to the CI. As a result the stimulation artifacts could not be removed by artifact removal on the bases of linear interpolation for recording electrodes ipsilateral to the CI. However, artifact-free responses could be obtained in all subjects from recording electrodes contralateral to the CI, when subject specific reference electrodes (Cz or Fpz) were used. EASSRs to modulation frequencies within the 30-50Â Hz range resulted in significant responses in all subjects. Only a small number of significant responses could be obtained, during a measurement period of 5Â min, that originate from the brain stem (i.e., modulation frequencies in the 80-100Â Hz range). This reduced synchronized activity of brain stem responses in long-term severely-hearing impaired CI users could be an attribute of processes associated with long-term hearing impairment and/or electrical stimulation.
Journal: Hearing Research - Volume 335, May 2016, Pages 149-160