Electrically Evoked Auditory Steady State Responses in Cochlear Implant Users

Abstract

Auditory steady state responses are neural potentials in response to repeated auditory stimuli. This study shows that electrically evoked auditory steady state responses (EASSRs) to low-rate pulse trains can be reliably recorded by electrodes placed on the scalp of a cochlear implant (CI) user and separated from the artifacts generated by the electrical stimulation. Response properties are described, and the predictive value of EASSRs for behaviorally hearing thresholds is analyzed. For six users of a Cochlear Nucleus CI, EASSRs to symmetric biphasic pulse trains with rates between 35 and 47 Hz were recorded with seven scalp electrodes. The influence of various stimulus parameters was assessed: pulse rate, stimulus intensity, monopolar or bipolar stimulation mode, and presentation of either one pulse train on one electrode or interleaved pulse trains with different pulse rates on multiple electrodes. To compensate for the electrical artifacts caused by the stimulus pulses and radio frequency transmission, different methods of artifact reduction were employed. The validity of the recorded responses was confirmed by recording on-off responses, determination of response latency across the measured pulse rates, and comparison of amplitude growth of stimulus artifact and response amplitude. For stimulation in the 40 Hz range, response latencies of 35.6 ms (SD = 5.3 ms) were obtained. Responses to multiple simultaneous stimuli on different electrodes can be evoked, and the electrophysiological thresholds determined from EASSR amplitude growth in the 40 Hz range correlate well with behaviorally determined threshold levels for pulse rates of 41 Hz.

Improved Electrically Evoked Auditory Steady-State Response Thresholds in Humans

“…Although the results presented in Hofmann and Wouters (2010) are encouraging, the implementation of an automatic fitting procedure for CIs in young children based on EASSRs still poses a number of methodological challenges: (1) the correlation between electrophysiological thresholds and behavioral T levels at clinically used pulse rates such as 900 pps is too low, (2) the used statistical methods for response detection are sensitive to any residual stimulus artifacts potentially resulting in erroneously detected responses, (3) the used response detection methods require the removal of stimulus artifacts as they cannot distinguish between neural response and stimulus artifacts, and (4) responses have mostly been recorded to bipolar stimulation, while, in clinical practice, most CIs are fit in monopolar mode.…”

“…The same six subjects as in Hofmann and Wouters (2010) took part in the experiments (Table 1). They were taking part voluntarily and signed an informed consent form.…”

“…In guinea pigs, stationary responses to direct electrical stimulation with sinusoidally amplitude-modulated stimuli can be measured that exhibit response characteristics similar to those of acoustically evoked responses (Jeng et al 2007(Jeng et al , 2008. In CI users, electrically evoked auditory steady-state responses (EASSRs) can be evoked by unmodulated low-rate pulse trains (Hofmann and Wouters 2010). Response properties in the 40 and 80-Hz range are similar to those of acoustically evoked responses, and electrophysiological thresholds derived from amplitude growth functions for pulse trains in the 40-Hz range have a very high correlation with behavioral T levels for 40 pps.…”

Objective Measures of Neural Processing of Interaural Time Differences

“…Work is currently underway to assess the IPM-FR in bilateral CI users. The EEG recording of steady-state responses in CI users is made challenging by the electrical artefacts created by stimulus pulses, but artefact rejection techniques have been successfully applied for the recording of AM-evoked steady-state responses (e.g., Hofmann and Wouters 2010). Such techniques should also be applicable for the recording of the IPM-FR.…”

Correlation between Preoperative Auditory Steady-State Response and Postoperative Electrically Evoked Auditory Brainstem Response and T Level in Cochlear Implantation for Child Patients with Inner-Ear Malformations

“…This is presently being applied as one of the routine examination items before cochlear implantation, with superiorities in frequency characteristics, maximum power output, objectivity, inspection efficiency, and insusceptibility to the influences of sleep and anesthesia. ASSR can make up the insufficiency of ABR through the following improvements: the stimuli used in ASSR have a fine frequency-specificity, the maximum output can reach as high as 115 dB, and the audiometry results are automatically judged by the system [13][14][15][16][17][18][19]. With origins of waves similar to those in ABR, EABR can theoretically reflect the functional state of the auditory pathway in the acoustic nerve of the brainstem, and it has a high extraction rate.…”