Electrically evoked amplitude modulation following response in cochlear implant candidates: comparison with auditory nerve response telemetry, subjective electrical stimulation, and speech perception

Intraoperative Neural Response Telemetry and Auditory Outcomes in Pediatric Cochlear Implantation

OBJECTIVE

To evaluate the relationship between intraoperative neural response telemetry (NRT) and postoperative auditory testing outcomes in children.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary-care academic center.

METHODS

Children who underwent cochlear implantation using the Cochlear Corporation device between 2010 and 2019 were included. Associations of average NRT and the slope of amplitude with postoperative auditory outcomes including functional auditory measure Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS), and speech perception testing (consonant-nucleus-consonant [CNC], Pediatric AzBio [BABY BIO], Hearing In Noise Test [HINT], and Northwestern University Children's Perception of Speech [NU-CHIPS]), measured between 6 and 57 months after implantation, were assessed using Spearman's rank correlation (ρ).

RESULTS

Thirty-eight patients (19 female, 19 male) and 54 ears were included. The median age of implantation was 20.6 months (range 9.6 months to 10.6 years). Eight (21%) children had neurologic disorders such as stroke, epilepsy, cerebral palsy, and other causes. Thirteen (34%) children had connexin mutations. Average NRT was not significantly correlated with postoperative auditory outcomes (IT-MAIS [ρ = -0.08, p = .74], CNC [ρ = 0.19, p = .32], BABY BIO [ρ = 0.21, p = .29], HINT [ρ = 0.05, p = .83]) and NU-CHIPS (ρ = 0.21, p = .28). The average slopes of amplitude and comfort level were not strongly correlated with any auditory outcomes (p > .05).

CONCLUSIONS

Intraoperative NRT was not correlated with any postoperative functional auditory outcomes. Patient counseling should include discussions that a subpar intraoperative cochlear response does not preclude favorable speech and auditory outcomes.

Acoustic Change Responses to Amplitude Modulation in Cochlear Implant Users: Relationships to Speech Perception

Objectives

The ability to understand speech is highly variable in people with cochlear implants (CIs) and to date, there are no objective measures that identify the root of this discrepancy. However, behavioral measures of temporal processing such as the temporal modulation transfer function (TMTF) has previously found to be related to vowel and consonant identification in CI users. The acoustic change complex (ACC) is a cortical auditory-evoked potential response that can be elicited by a “change” in an ongoing stimulus. In this study, the ACC elicited by amplitude modulation (AM) change was related to measures of speech perception as well as the amplitude detection threshold in CI users.

Methods

Ten CI users (mean age: 50 years old) participated in this study. All subjects participated in behavioral tests that included both speech and amplitude modulation detection to obtain a TMTF. CI users were categorized as “good” (n = 6) or “poor” (n = 4) based on their speech-in noise score (<50%). 64-channel electroencephalographic recordings were conducted while CI users passively listened to AM change sounds that were presented in a free field setting. The AM change stimulus was white noise with four different AM rates (4, 40, 100, and 300 Hz).

Results

Behavioral results show that AM detection thresholds in CI users were higher compared to the normal-hearing (NH) group for all AM rates. The electrophysiological data suggest that N1 responses were significantly decreased in amplitude and their latencies were increased in CI users compared to NH controls. In addition, the N1 latencies for the poor CI performers were delayed compared to the good CI performers. The N1 latency for 40 Hz AM was correlated with various speech perception measures.

Conclusion

Our data suggest that the ACC to AM change provides an objective index of speech perception abilities that can be used to explain some of the variation in speech perception observed among CI users.

Brain Plasticity Can Predict the Cochlear Implant Outcome in Adult-Onset Deafness

Sensory plasticity, which is associated with deafness, has not been as thoroughly investigated in the adult brain as it has in the developing brain. In this study, we examined the brain reorganization induced by auditory deprivation in people with adult-onset deafness and its clinical relevance by measuring glucose metabolism before cochlear implant (CI) surgery. F-18 fluorodeoxyglucose positron emission tomography (¹⁸F-FDG-PET) scans were performed in 37 postlingually deafened patients during the preoperative workup period, and in 39 normal-hearing (NH) controls. Behavioral CI outcomes were measured at 1 year after implantation using a phoneme identification test with auditory cueing only. In the deaf individuals, areas involved in the auditory pathway such as the inferior colliculus and bilateral superior temporal gyri were hypometabolic compared to the NH controls. The hypometabolism observed in the deaf auditory cortices gradually returned to levels similar to the controls as the duration of deafness increased. However, contrary to our previous findings in congenitally deaf children, this metabolic recovery failed to have a significant prognostic value for the recovery of the speech perception ability in adult CI patients. In a broad occipital area centered on the primary visual cortices, glucose metabolism was higher in the deaf patients than the controls, suggesting that the area had become visually hyperactive for sensory compensation immediately after the onset of deafness. In addition, a negative correlation between the metabolic activity and behavioral speech perception outcomes was observed in the visual association areas. In the medial frontal cortices, cortical metabolism in most patients decreased, but patients who had preserved metabolic activities showed better speech performance. These results suggest that the auditory cortex in people with adult-onset deafness is relatively resistant to cross-modal plasticity, and instead, individual traits in late-stage visual processing and cognitive control seem to be more reliable prognostic markers for adult-onset deafness.

Evaluation of Temporal Difference Limen in Preoperative Non-Invasive Ear Canal Audiometry as a Predictive Factor for Speech Perception after Cochlear Implantation

The temporal difference limen (TDL) can be measured with noninvasive electrical ear canal stimulation. The objective of the study wa to determine the role of preoperative TDL measurements in predicting patients’ speech perception after cochlear implantation. We carried out a retrospective chart analysis of fifty-four cochlear implant (CI) patients with preoperative TDL and postoperative bisyllabic word recognition measurements in Helsinki University Central Hospital between March 1994 and March 2011. Our results show that there is no correlation between TDL and postoperative speech perception. However, patient’s advancing age correlates with longer TDL but not-directly with poorer speech perception. The results are in line with previous results concerning the lack of predictive value of preoperativ TDL measurements in CI patients.