Towards single-trial classification of invasively recorded auditory evoked potentials in cochlear implant users.

Objective.One promising approach towards further improving cochlear implants (CI) is to use brain signals controlling the device in order to close the auditory loop. Initial electroencephalography (EEG) studies have already shown promising results. However, they are based on noninvasive measurements, whereas implanted electrodes are expected to be more convenient in terms of everyday-life usability. If additional measurement electrodes were implanted during CI surgery, then invasive recordings should be possible. Furthermore, implantation will provide better signal quality, higher robustness to artefacts, and thus enhanced classification accuracy.Approach.In an initial project, three additional epidural electrodes were temporarily implanted during the surgical procedure. After surgery, different auditory evoked potentials (AEPs) were recorded both invasively (epidural) and using surface electrodes, with invasively recorded signals demonstrated as being markedly superior. In this present analysis, cortical evoked response audiometry (CERA) signals recorded in seven patients were used for single-trial classification of sounds with different intensities. For classification purposes, we used shrinkage-regularized linear discriminant analysis (sLDA). Clinical speech perception scores were also investigated.Main results.Analysis of CERA data from different subjects showed single-trial classification accuracies of up to 99.2% for perceived vs. non-perceived sounds. Accuracies of up to 89.1% were achieved in classification of sounds perceived at different intensities. Highest classification accuracies were achieved by means of epidural recordings. Required loudness differences seemed to correspond to speech perception in noise.Significance.The proposed epidural recording approach showed good classification accuracy into sound perceived and not perceived when the best-performing electrodes were selected. Classifying different levels of sound stimulation accurately proved more challenging. At present, the methods explored in this study would not be sufficiently reliable to allow automated closed-loop control of CI parameters. However, our findings are an important initial contribution towards improving applicability of closed auditory loops and for next-generation automatic fitting approaches.

Monitoring of the auditory pathway maturation after early intervention during the first year of life in infants with sensorineural hearing loss.

PURPOSE: The objective of this study was to investigate the auditory pathway maturation monitored by auditory brainstem responses (ABR) in infants with hearing loss during the first year of life. ABR were used to estimate hearing thresholds and the effect of early intervention strategies using hearing aids (HA). METHODS: Click-evoked ABRs were measured in 102 infants aged from 0 to 12 months to determine their individual auditory threshold. Early therapy intervention was recommended before 12 months of age and analyzed. To evaluate the effect of hearing amplification on auditory maturation, different subgroups of infants with moderate hearing loss were analyzed and the auditory pathway maturation was determined based on IPL I-V shortening. RESULTS: Overall, 110 ears (54.0% of 204 ears) with mild to profound HL showed threshold changes of 10 dB up to 60 dB in the follow-up ABR testing. HA were prescribed at the age of 3.8 ± 3.9 months. Cochlear implantation (CI) was performed in cases of repeated profound HL at the age of 9.9 months ± 4.5 months. A significant shortening of IPL I-V in all subgroups of infants (with and without risk factors) who received HA was shown and assumed auditory pathway maturation. CONCLUSION: An early intervention using optimally fitted HA influenced auditory pathway maturation and may lead to improvements of hearing thresholds during the first year of life in infants. This study underscores the importance of not only providing HAs to infants, but also controlling for hearing threshold changes ensuring that HAs provide the optimal level of intervention or CI is indicated.

Epidural recordings in cochlear implant users.

OBJECTIVE: In the long term it is desirable for CI users to control their device via brain signals. A possible strategy is the use of auditory evoked potentials (AEPs). Several studies have shown the suitability of auditory paradigms for such an approach. However, these investigations are based on non-invasive recordings. When thinking about everyday life applications, it would be more convenient to use implanted electrodes for signal acquisition. Ideally, the electrodes would be directly integrated into the CI. Further it is to be expected that invasively recorded signals have higher signal quality and are less affected by artifacts. APPROACH: In this project we investigated the feasibility of implanting epidural electrodes temporarily during CI surgery and the possibility to record AEPs in the course of several days after implantation. Intraoperatively, auditory brainstem responses were recorded, whereas various kinds of AEPs were recorded postoperatively. After a few days the epidural electrodes were removed. MAIN RESULTS: Data sets of ten subjects were obtained. Invasively recorded potentials were compared subjectively and objectively to clinical standard recordings using surface electrodes. Especially the cortical evoked response audiometry depicted clearer N1 waves for the epidural electrodes which were also visible at lower stimulation intensities compared to scalp electrodes. Furthermore the signal was less disturbed by artifacts. The objective quality measure (based on data sets of six patients) showed a significant better signal quality for the epidural compared to the scalp recordings. SIGNIFICANCE: Altogether the approach revealed to be feasible and well tolerated by the patients. The epidural recordings showed a clearly better signal quality than the scalp recordings with AEPs being clearer recognizable. The results of the present study suggest that including epidural recording electrodes in future CI systems will improve the everyday life applicability of auditory closed loop systems for CI subjects.

[Discrimination of musical pitch with cochlear implants]. / Diskrimination musikalischer Tonhöhen bei Patienten mit Kochleaimplantat.

BACKGROUND: Numerous people with cochlear implants (CI) report difficulties in listening to music even though they understand speech quite well. One reason for this is a limited perception of pitch and timbre. In this study ability of adult CI subjects to discriminate musical pitch is investigated. PATIENTS AND METHODS: In two psychoacoustic experiments, each conducted in 10 adult CI subjects provided with MED-EL Combi 40+ cochlear implant devices and a control group of subjects with normal hearing, individual discrimination abilities for musical pitch perception were determined. To investigate the influence of the group of instruments on discrimination ability, stimuli representing four different groups of instruments were used: woodwind (clarinet), brass (trumpet), strings (violin) and keyboard instruments (piano). RESULTS: The discrimination thresholds determined varied between individual CI subjects, and on average they were significantly higher for the piano than for the other three instruments. CONCLUSIONS: The results show that in subjects with CI pitch perception differs from instrument to instrument and is in general worse than in persons with normal hearing.

[Radiological findings in bilharziasis of the urinary tract]. / Radiologische Befunde bei der Bilharziose des Harntraktes.

Bilharzia of the urinary tract has characteristic radiological changes; because of the increase in this disease, it is important to be familiar with these. The typical changes are demonstrated in six patients and could be seen on abdominal films, tomography of the pelvis, excretion urography and computed tomography. The paper is supplemented by a description of the area in which the disease is endemic.