Takako Iwaki

Sign language ‘heard’ in the auditory cortex

The upper regions of the brains temporal lobe are important both for hearing and for comprehending spoken language. We have discovered that these regions can be activated by sign language in congenitally deaf subjects, even though the temporal lobe normally functions as an auditory area. This finding indicates that, in deaf people, the brain region usually reserved for hearing may be activated by other sensory modalities, providing striking evidence of neural plasticity.

Different forms of dizziness occurring after cochlear implant

Abstract Dizziness after cochlear implant (CI) was studied in a series of 94 consecutive adult patients receiving a cochlear implant, 46 (49.0%) of whom experienced dizziness post-operatively. In 29 patients, post-operative dizziness occurred soon after surgery and subsided within one month. Dizziness of the continuous type, lasting more than 6 months, was a complaint in only two patients. In addition to these already known forms of dizziness, spells of vertigo occurring later than one month after cochlear implant were experienced by 15 patients (delayed-V). The spells of delayed-V occurred suddenly and persisted for several hours. Moreover, 85.7% of delayed-V patients complained of hearing and tinnitus abnormalities during these spells. The clinical features of delayed-V were similar to those in patients with Ménière’s disease. The preoperative bithermal caloric test showed a significantly higher response for the delayed-V group than the other groups (ANOVA: P < 0.05) in terms of slow phase eye velocity of caloric nystagmus. These findings suggest that inner ear lesions due to cochlear implant surgery develop gradually. Similarities in clinical features between delayed-V and Ménière’s disease indicate the presence of labyrinthine hydrops.

Successful cochlear implantation in prelingual profound deafness resulting from the common 233delC mutation of the GJB2 gene in the Japanese

Objectives Recently, we identified three novel mutations of the GJB2 gene in Japanese families with autosomal‐recessive non‐syndromic deafness. 1 Seven of 11 mutated chromosomes (63.6%) contained a 233delC allele, suggesting that the 233delC mutation is the most common mutation of the GJB2 gene in the Japanese population. After it was recognized that cochlear implantation (CI) is of benefit to children with prelingual deafness, we have had a number of prelingual pediatric CI patients. Because children carrying the homozygous 233delC mutation show bilateral prelingual profound deafness, they could be enrolled in the CI program at Osaka University Graduate School of Medicine. The purposes of this study were 1) to analyze the occurrence of the GJB2 mutations in our 15 prelingual pediatric CI patients in whom the cause of non‐syndromic deafness was unknown, and 2) to evaluate the auditory function and postoperative speech perception with CI of those GJB2‐related deaf subjects.

Neural plasticity detected in short- and long-term cochlear implant users using PET.

The interaction of listening to words and watching sign language in short-term and long-term cochlear implant (CI) users who have learned sign language after becoming deaf was measured using PET. In short-term CI users the auditory cortex was inactive while in long-term CI users it was fully activated with the simultaneous presentation of auditory and visual input. The result suggests the possibility that the interference of rival modalities may be diminished with experience and the preference switchover from the visual input to the auditory input could be accomplished by means of the neural plasticity persisting in the mature human auditory cortex.

Comparison of speech perception between monaural and binaural hearing in cochlear implant patients

Objective To assess the advantages of binaural hearing for cochlear implant (CI) users using a hearing aid (HA) for the contralateral ear. Material and Methods The subjects comprised 3 males and 3 females (age range 48–84 years). All of them had been using a CI and HA for >6 months. Their speech perception was examined in quiet using monosyllables and Japanese Hearing in Noise Test (J-HINT) sentences. Speech perception in noise was examined using J-HINT sentences. Late cortical waves were measured while subjects listened to 1 kHz frequent and 2 kHz target tone stimuli. The latency of the event-related potential (P300) wave was compared for monaural and binaural hearing conditions. Results Three subjects showed significantly better results for binaural than monaural (CI alone) hearing for monosyllables and HINT sentences (p<0.05; paired t-test). Subjects with better speech perception had been using an HA for longer than those with poor performance (18.3 vs 4.0 years). The overall average score was better for binaural than monaural hearing in the speech perception test under quiet and noisy conditions. Comparison of the latency of the P300 wave under monaural and binaural hearing conditions showed a significantly shorter latency for the latter (p=0.02; paired t-test). Conclusion Although the use of an HA alone showed marginal benefit for CI users, binaural hearing (CI + HA) resulted in a significant improvement in speech perception under various circumstances.

Significance of auditory evoked responses (EABR and P300) in cochlear implant subjects

An electrically derived auditory brainstem response (EABR) was recorded intra-operatively, and the event-related potential (P300) postoperatively in post-lingually deaf adult cochlear implantees. EABR and P300 were recorded from two groups of 25 subjects each. All subjects had a cochlear mini-22 system implanted at our center between 1994 and 1998. Two parameters of EABR, threshold (T) and the gradient of the amplitude-growth (AG) curve, were used for correlation with postoperative speech reception scores. The consonant recognition score (CRS) measured 1 month postoperatively showed a significant correlation with the AG curve of EABR (Spearman rank order test, p=0.004), but not at later points in time. No correlation was found between the T and CRS at any time postoperatively. As the AG curve reflects the number of remaining spiral ganglion cells in the inner ear, a large number of surviving neurons is thought to be advantageous only for initial speech learning. The latency of P300 was measured for correlation with the speech reception score. The division of the cochlear implant subjects into a fair and a good hearing group according to their CRS showed that the average latency of P300 was significantly longer for the fair hearing group than for the good hearing group. A follow-up study showed that P300 latency significantly correlated with CRS measured at 6 months, 1 year and at a later time. As the latency of P300 is thought to reflect the time for sound processing in the central auditory system, our results indicate that plasticity of the central auditory system is more important than that of the peripheral auditory system for speech learning in cochlear implant subjects.An electrically derived auditory brainstem response (EABR) was recorded intra-operatively, and the event-related potential (P300) postoperatively in post-lingually deaf adult cochlear implantees. EABR and P300 were recorded from two groups of 25 subjects each. All subjects had a cochlear mini-22 system implanted at our center between 1994 and 1998. Two parameters of EABR, threshold (T) and the gradient of the amplitude-growth (AG) curve, were used for correlation with postoperative speech reception scores. The consonant recognition score (CRS) measured 1 month postoperatively showed a significant correlation with the AG curve of EABR (Spearman rank order test, p = 0.004), but not at later points in time. No correlation was found between the T and CRS at any time postoperatively. As the AG curve reflects the number of remaining spiral ganglion cells in the inner ear, a large number of surviving neurons is thought to be advantageous only for initial speech learning. The latency of P300 was measured for correlation with the speech reception score. The division of the cochlear implant subjects into a fair and a good hearing group according to their CRS showed that the average latency of P300 was significantly longer for the fair hearing group than for the good hearing group. A follow-up study showed that P300 latency significantly correlated with CRS measured at 6 months, 1 year and at a later time. As the latency of P300 is thought to reflect the time for sound processing in the central auditory system, our results indicate that plasticity of the central auditory system is more important than that of the peripheral auditory system for speech learning in cochlear implant subjects.

Auditory plasticity in cochlear implant patients

Dynamic range (DR) of cochlear implant electrodes and speech recognition scores (SRS) were chronologically studied in 23 post-lingually deaf subjects over a period of one year. DR significantly increased over one year (ANOVA, p = 0.03). When DR was compared among three groups of electrodes which were located in the inferior, ascending and superior segments of the cochlear basal turn, that in the superior segment showed the largest increase (p = 0.001), followed by those in the ascending and inferior segments. Vowel and consonant recognition scores with auditory cue were best 6 months after operation and were maintained at the level for one year. Although the time course of improvement differed between DR and SRS, a significant positive correlation was observed at 12 months after operation. Improvement of SRS could be a result of a DR increase in the superior segment of the cochlea, which should convey pitch information over the mid-frequency region.

Cortical processing of tactile language in a postlingually deaf-blind subject.

We compared neural activation detected by magnetoencephalography (MEG) during tactile presentation of words and non-words in a postlingually deaf-blind subject and six normal volunteers. The left postcentral gyrus, bilateral inferior frontal gyri, left posterior temporal lobe, right anterior temporal lobe, bilateral middle occipital gyri were activated when tactile words were presented to the right hand of the deaf-blind subject. This set of activated regions was not observed in the normal volunteers, although activation of several combinations of these regions was detected. Positron emission tomography confirmed the location of the MEG-activated areas in the deaf-blind subject. Our results demonstrated that the deaf-blind subject is heavily involved in interpreting tactile language by enhancing cortical activation of cognitive and semantic processing.

Assessing binaural/bimodal advantages using auditory event-related potentials in subjects with cochlear implants

OBJECTIVE To assess the advantage of binaural and bimodal hearing for subjects with cochlear implant (CI) using auditory event-related potentials as well as speech perception tests. SUBJECTS AND METHODS The subjects comprised four binaural CI users (CI/CI group) and eleven bimodal CI users, who wore a hearing aid (HA) contralaterally (CI/HA group). All subjects had used binaural or bimodal fitting for over 6 months. Their speech perception was examined in a quiet environment using monosyllabic words. Late cortical waves were measured while subjects were engaged in an oddball task of 1kHz frequent and 2kHz rare tone stimuli. The latencies of event-related potential (N1, N2, P3) were compared for monaural, binaural, and bimodal hearing conditions. RESULTS Significantly (p<0.01, paired t-test) better speech perception for monosyllabic words was found for both binaural and bimodal hearing than monaural hearing. The latency of N1 did not significantly change for either binaural or bimodal hearing. On the other hand, the latency of N2 was significantly (p<0.01, paired t-test) shorter for binaural and bimodal hearing than for monaural hearing. The latency of P3 was shorter for binaural and bimodal hearing than monaural hearing in all subjects, and the difference was statistically significant in both CI/CI and CI/HA groups (p<0.01, paired t-test). CONCLUSIONS Better speech perception was obtained for binaural and bimodal hearing than for monaural hearing in CI subjects. The results obtained in the comparison of P3 latency agreed with that of speech perception. Thus, using bilateral hearing devices is recommended for CI subjects. We also found that event-related potentials were useful as an objective tool to assess the advantage of binaural and bimodal hearing for CI subjects.

Auditory and tactile processing in a postmeningitic deaf–blind patient with a cochlear implant

The authors examined the neural function of a postmeningitic deaf–blind patient who regained his hearing with a multichannel cochlear implant. Auditory stimuli activated the temporal cortices of both sides in a manner similar to that of controls, reflecting the successful recruitment of the auditory cortex after implantation. The patient’s occipital lobes were deactivated during the tactile language task, the results of which were completely different from those before cochlear implantation.