The timecourse of multisensory speech processing in unilaterally stimulated cochlear implant users revealed by ERPs

Preoperative EABR evaluation of auditory pathway integrity in patients with different etiology and postoperative effect estimation

OBJECTIVES

To evaluate the effect of electrical auditory brainstem response (EABR) on the integrity evaluation of auditory pathway and the prediction of postoperative effect of cochlear implantation in patients with different etiology of hearing loss.

METHODS

A total of 580 patients with neuropathic deafness who underwent cochlear implantation surgery from August 2011 to December 2020 were selected for EABR test. The preoperative EABR waveform was analyzed, and parameters such as V wave amplitude, threshold, latency and interval of each wave, and slope of V wave I/O curve were measured. Neural response telemetry (NRT) test was performed during MAP 1 month after operation, and C and T values of the machine were recorded.

RESULTS

The total EABR extraction rate was 98.45% among 580 patients, including 100% for the normal structure group and enlarged vestibular aqueduct group (LVAS), 92.44% for other malformed group. The average threshold of V wave in patients with normal cochlear structure was significantly better than the malformation groups (p < 0.05). The total extraction rate of NRT was 78.62%, including 99.72% in the group with normal structure, 95.65% in the LVAS group, 1.85-88.24% in the group with other malformations, and 0% in the cochlear ossification group. The correlation analysis showed a statistically significant correlation between the average preoperative EABR threshold and the C value of NRT.

CONCLUSIONS

Preoperative EABR could evaluate the integrity of auditory conduction pathway of patients with cochlear implantation and predict the postoperative hearing rehabilitation effect.

Exploring neurocognitive factors and brain activation in adult cochlear implant recipients associated with speech perception outcomes-A scoping review

Background

Cochlear implants (CIs) are considered an effective treatment for severe-to-profound sensorineural hearing loss. However, speech perception outcomes are highly variable among adult CI recipients. Top-down neurocognitive factors have been hypothesized to contribute to this variation that is currently only partly explained by biological and audiological factors. Studies investigating this, use varying methods and observe varying outcomes, and their relevance has yet to be evaluated in a review. Gathering and structuring this evidence in this scoping review provides a clear overview of where this research line currently stands, with the aim of guiding future research.

Objective

To understand to which extent different neurocognitive factors influence speech perception in adult CI users with a postlingual onset of hearing loss, by systematically reviewing the literature.

Methods

A systematic scoping review was performed according to the PRISMA guidelines. Studies investigating the influence of one or more neurocognitive factors on speech perception post-implantation were included. Word and sentence perception in quiet and noise were included as speech perception outcome metrics and six key neurocognitive domains, as defined by the DSM-5, were covered during the literature search (Protocol in open science registries: 10.17605/OSF.IO/Z3G7W of searches in June 2020, April 2022).

Results

From 5,668 retrieved articles, 54 articles were included and grouped into three categories using different measures to relate to speech perception outcomes: (1) Nineteen studies investigating brain activation, (2) Thirty-one investigating performance on cognitive tests, and (3) Eighteen investigating linguistic skills.

Conclusion

The use of cognitive functions, recruiting the frontal cortex, the use of visual cues, recruiting the occipital cortex, and the temporal cortex still available for language processing, are beneficial for adult CI users. Cognitive assessments indicate that performance on non-verbal intelligence tasks positively correlated with speech perception outcomes. Performance on auditory or visual working memory, learning, memory and vocabulary tasks were unrelated to speech perception outcomes and performance on the Stroop task not to word perception in quiet. However, there are still many uncertainties regarding the explanation of inconsistent results between papers and more comprehensive studies are needed e.g., including different assessment times, or combining neuroimaging and behavioral measures.

Systematic review registration

https://doi.org/10.17605/OSF.IO/Z3G7W.

Features of beta-gamma phase-amplitude coupling in cochlear implant users derived from EEG

Cochlear implants (CIs) allow patients with severe to profound hearing loss to gain or regain their sense of hearing. However, the objective assessment of auditory rehabilitation in CI users remains a challenge. In particular, the utility of phase-amplitude coupling (PAC) for evaluating postoperative rehabilitation of CI users remains unknown. In the present study, we conducted an oddball paradigm with stimuli varying in sample speech syllables and collected electroencephalography (EEG) signals for 10 CI users at the time the implant was activated and 180 days after activation. Twelve normal-hearing subjects served as controls. We explored the oscillatory properties of the neural response to syllable incongruence and the cross-frequency coupling between multiple frequencies in CI users. We found that beta-gamma coupling appeared to be enhanced in CI users compared with normal controls and this difference gradually disappeared with increasing implantation time. The present results suggest that predictively encoded auditory pathways are gradually restored in CI users. In addition, the PAC feature in unilateral CI users was found to be lateralized in the auditory cortex, which was consistent with previous studies of auditory-evoked cortical activity. Therefore, PAC may be a reference biomarker for the rehabilitation of speech discrimination in CI users.

Age effects on cognitive functions and speech-in-noise processing: An event-related potential study with cochlear-implant users and normal-hearing listeners

A cochlear implant (CI) can partially restore hearing in individuals with profound sensorineural hearing loss. However, electrical hearing with a CI is limited and highly variable. The current study aimed to better understand the different factors contributing to this variability by examining how age affects cognitive functions and cortical speech processing in CI users. Electroencephalography (EEG) was applied while two groups of CI users (young and elderly; N = 13 each) and normal-hearing (NH) listeners (young and elderly; N = 13 each) performed an auditory sentence categorization task, including semantically correct and incorrect sentences presented either with or without background noise. Event-related potentials (ERPs) representing earlier, sensory-driven processes (N1-P2 complex to sentence onset) and later, cognitive-linguistic integration processes (N400 to semantically correct/incorrect sentence-final words) were compared between the different groups and speech conditions. The results revealed reduced amplitudes and prolonged latencies of auditory ERPs in CI users compared to NH listeners, both at earlier (N1, P2) and later processing stages (N400 effect). In addition to this hearing-group effect, CI users and NH listeners showed a comparable background-noise effect, as indicated by reduced hit rates and reduced (P2) and delayed (N1/P2) ERPs in conditions with background noise. Moreover, we observed an age effect in CI users and NH listeners, with young individuals showing improved specific cognitive functions (working memory capacity, cognitive flexibility and verbal learning/retrieval), reduced latencies (N1/P2), decreased N1 amplitudes and an increased N400 effect when compared to the elderly. In sum, our findings extend previous research by showing that the CI users' speech processing is impaired not only at earlier (sensory) but also at later (semantic integration) processing stages, both in conditions with and without background noise. Using objective ERP measures, our study provides further evidence of strong age effects on cortical speech processing, which can be observed in both the NH listeners and the CI users. We conclude that elderly individuals require more effortful processing at sensory stages of speech processing, which however seems to be at the cost of the limited resources available for the later semantic integration processes.

Evidence of visual crossmodal reorganization positively relates to speech outcomes in cochlear implant users

Deaf individuals who use a cochlear implant (CI) have remarkably different outcomes for auditory speech communication ability. One factor assumed to affect CI outcomes is visual crossmodal plasticity in auditory cortex, where deprived auditory regions begin to support non-auditory functions such as vision. Previous research has viewed crossmodal plasticity as harmful for speech outcomes for CI users if it interferes with sound processing, while others have demonstrated that plasticity related to visual language may be beneficial for speech recovery. To clarify, we used electroencephalography (EEG) to measure brain responses to a partial face speaking a silent single-syllable word (visual language) in 15 CI users and 13 age-matched typical-hearing controls. We used source analysis on EEG activity to measure crossmodal visual responses in auditory cortex and then compared them to CI users' speech-in-noise listening ability. CI users' brain response to the onset of the video stimulus (face) was larger than controls in left auditory cortex, consistent with crossmodal activation after deafness. CI users also produced a mixture of alpha (8-12 Hz) synchronization and desynchronization in auditory cortex while watching lip movement while controls instead showed desynchronization. CI users with higher speech scores had stronger crossmodal responses in auditory cortex to the onset of the video, but those with lower speech scores had increases in alpha power during lip movement in auditory areas. Therefore, evidence of crossmodal reorganization in CI users does not necessarily predict poor speech outcomes, and differences in crossmodal activation during lip reading may instead relate to strategies or differences that CI users use in audiovisual speech communication.