Chie Obuchi

Auditory Evoked Potentials under Active and Passive Hearing Conditions in Adult Cochlear Implant Users

Objectives Speech perception abilities, which vary widely among cochlear implant (CI) users, are considered to be associated with the integrity of the central auditory pathways from the auditory nerve to the cortex. Therefore, auditory evoked potentials (AEPs) are used to evaluate central auditory processing, which is thought to contribute to speech perception in CI subjects. In AEPs, the P300 component reflects the cognitive ability of subjects to detect and respond to stimuli and has most frequently been used and investigated in CI subjects. Other studies have used mismatched negativity (MMN) to examine central auditory processing. It is important to compare MMN and P300 and examine the auditory processing mechanisms involved in these components. Our study therefore aimed to investigate the relationship between P300 and MMN using both active and passive hearing paradigms in CI and normal hearing (NH) subjects. Methods Our subjects consisted of 3 CI subjects and 3 NH subjects. An oddball paradigm was used to deliver the stimuli on both components. The frequent stimuli were 1,000-Hz tone bursts, whereas the rare stimuli were 1,500, 2,000, and 4,000-Hz. Results As the frequency contrasts increased, the P3 latencies increased in the CI subjects. However, the latency in NH subjects did not change significantly across the frequency contrast conditions. MMNs were identified for both the CI and NH subjects; the latencies in the CI subjects were longer than those in the NH subjects. However, there were no differences in the latencies of either the CI or NH subjects in the 3 frequency contrast tasks. Conclusion Our results indicated that different auditory processing pathways are involved in the active and passive hearing conditions based on the P300 and MMN data and that a combination of both responses plays an important role in the comprehension of auditory processing mechanisms in CI subjects.

A novel frameshift mutation in KCNQ4 in a family with autosomal recessive non-syndromic hearing loss.

Mutation of KCNQ4 has been reported to cause autosomal dominant non-syndromic hearing loss (DFNA2A) that usually presents as progressive hearing loss starting from mild to moderate hearing loss during childhood. Here, we identified a novel KCNQ4 mutation, c.1044_1051del8, in a family with autosomal recessive non-syndromic hearing loss. The proband was homozygous for the mutation and was born to consanguineous parents; she showed severe hearing loss that was either congenital or of early childhood onset. The proband had a sister who was heterozygous for the mutation but showed normal hearing. The mutation caused a frameshift that eliminated most of the cytoplasmic C-terminus, including the A-domain, which has an important role for protein tetramerization, and the B-segment, which is a binding site for calmodulin (CaM) that regulates channel function via Ca ions. The fact that the heterozygote had normal hearing indicates that sufficient tetramerization and CaM binding sites were present to preserve a normal phenotype even when only half the proteins contained an A-domain and B-segment. On the other hand, the severe hearing loss in the homozygote suggests that complete loss of the A-domain and B-segment in the protein caused loss of function due to the failure of tetramer formation and CaM binding. This family suggests that some KCNQ4 mutations can cause autosomal recessive hearing loss with more severe phenotype in addition to autosomal dominant hearing loss with milder phenotype. This genotype-phenotype correlation is analogous to that in KCNQ1 which causes autosomal dominant hereditary long QT syndrome 1 with milder phenotype and the autosomal recessive Jervell and Lange-Nielsen syndrome 1 with more severe phenotype due to deletion of the cytoplasmic C-terminus of the potassium channel.

Auditory symptoms and psychological characteristics in adults with auditory processing disorders

Most adults with auditory processing disorder (APD) often have trouble at work. It is possible that these listening problems in adults with APD influence their mental health. Thus, we have to take the subjects personality and mental status into consideration when supporting subjects with APD. However, studies on APD in adults are comparatively rare. In this study, we aimed to evaluate the relationships between the results of auditory tests, APD symptoms, and psychological status in subjects with APD. This study included 22 adults who complained of listening problems in everyday life, and they underwent auditory processing tests and were questioned regarding their psychological characteristics. From the results of the auditory processing tests, all subjects showed low scores on at least one test; therefore, they were suspected of having APD. Especially, the scores were low on the auditory memory test. Furthermore, subjects with APD show relatively similar psychological characteristics to each other. However, there was no significant relationship between the results of the auditory processing tests and psychological characteristics. We have to take notice of a subjects psychological state when they perceive their listening difficulties as a large-scale problem and feel anxious as a result. For this purpose, we should take psychological characteristics into consideration at the time of the medical examination interview before audio-psychological testing.

Binaural integration abilities in bilateral cochlear implant user

Bilateral Cochlear implants (CIs) improved speech intelligibility, speech perception in background noise, and sound localization in quiet and noisy situations. However, it is unclear whether these advantages essentially result in binaural integration of acoustic stimuli from each ear. In this study, we investigated the effectiveness of binaural integration by bilateral CIs placement using binaural hearing tests and subjective auditory perceptual assessment. A 61-year-old bilateral CIs subject underwent the following four tests: the Japanese Hearing in Noise Test (HINT-J), the dichotic listening test (DLT), the Rapidly Alternating Speech Perception (RASP) test, and subjective auditory perceptual assessment. The HINT-J score was significantly higher for bilateral CIs than for a unilateral CI. However, DLT and the RASP test revealed contradictory results. Subjective auditory perceptual assessment revealed active and bright impressions for bilateral hearing, which were also noisy and strong compared with those for unilateral hearing. The results of this study revealed that bilateral CIs improved speech perception in background noise and an improved auditory impression, although the bilateral integration abilities were not improved. This was probably because the patient was required to combine information from the two ears into a single perception in DLT and the RASP test. More longitudinal data should be collected and analyzed in future studies to evaluate the long-term effects of bilateral CIs.