Effects of the Conductive Component of Hearing Loss on Speech Discrimination Ability

The effect of aging and asymmetrical hearing on speech discrimination

BACKGROUND

Speech discrimination (SpD) is exacerbated by hearing loss, but the relationship between pure-tone audiometry (PTA) and SpD is poorly described and understood in the aging process. It is also unclear whether severity of left-right (L-R) differences in PTA threshold disproportionately affects SpD.

METHODS

We conducted a retrospective cross-sectional study of a broad age range (10-99 years) of patients in Japan. Demographic data, SpD, and PTA threshold data were collected for each patient and side (L-R). We evaluated the association between chronological age and overall SpD, and SpD according to severity of PTA-threshold difference for ear pairs. Asymmetries in L-R PTA thresholds were stratified into four equally spaced categories: <10dB L-R difference to ≥40 dB L-R difference.

RESULTS

Among the 2760 eligible participants, data from 5508 ears are analyzed. Overall SpD gradually decreases with age, with SpD scores in the oldest groups being significantly worse (Kruskal-Wallis followed by Dunn's test; p < 0.0001) than those of the youngest group. Comparison of worse-hearing ears to better-hearing ears within the same severity of hearing impairment reveals significant differences on SpD in ears that have moderate or severe hearing impairment (p < 0.0001). Post-hoc analysis identifies significant differences in SpD between the worse-hearing ears and the better-hearing ears that have hearing differences of 20 dB or more.

CONCLUSIONS

SpD is dramatically affected by age and asymmetrical hearing. Therefore, appropriate audiological interventions should be proactively considered according to an individual's hearing level, age, and difference in L-R hearing levels.

The association between dietary total antioxidant capacity and hearing loss: results from the Tehran employees Cohort Study

BACKGROUND

Despite numerous studies that have explored the association between individual antioxidants or specific combinations and the risk of hearing loss, there is lack of information regarding the relationship between dietary total antioxidant capacity (dTAC) and hearing loss. The conflicting results on this association further highlight the need for more research in this area. This study aims to investigate the association between overall dietary antioxidant intake and the risk of hearing loss among Iranian adults.

METHODS

This cross-sectional study recruited 3443 adult participants aged between 19 and 67 years (with an average age of 41.4 years ± 8.8) who were employed at Tehran University of Medical Sciences in Iran. Participants underwent dietary assessment using a validated Food Frequency Questionnaire (FFQ). The hearing status of each participant was evaluated by a licensed audiologist in a soundproof room, using diagnostic audiometry that adhered to American National Standards specifications and followed standard audiometric clinical procedures. The dietary total antioxidant capacity (dTAC) was calculated using the Ferric Reducing-Antioxidant Power (FRAP) values.

RESULTS

43.6% of male participants had hearing loss, while 26.8% among female participants. After accounting for various confounding factors, no significant association was observed between higher levels of dTAC and reduced odds of hearing loss in the overall population. However, among men under the age of 40, higher levels of dTAC were associated with decreased odds of hearing loss, even after adjusting for several covariates (OR: 0.56, 95% CI: 0.31-1.02, Ptrend = 0.02). This relationship was not evident in men over 40 years of age or among women.

CONCLUSION

The study found an inverse relationship between higher antioxidant intake in the diet and lower odds of hearing loss, specifically among men who were 40 years old or younger. However, this relationship was not observed in the overall population or among women. Additional prospective studies are necessary to validate these results.

Associations of hearing loss and structural changes in specific cortical regions: a Mendelian randomization study

INTRODUCTION

Previous studies have suggested a correlation between hearing loss (HL) and cortical alterations, but the specific brain regions that may be affected are unknown.

METHODS

Genome-wide association study (GWAS) data for 3 subtypes of HL phenotypes, sensorineural hearing loss (SNHL), conductive hearing loss, and mixed hearing loss, were selected as exposures, and GWAS data for brain structure-related traits were selected as outcomes. The inverse variance weighted method was used as the main estimation method.

RESULTS

Negative associations were identified between genetically predicted SNHL and brain morphometric indicators (cortical surface area, cortical thickness, or volume of subcortical structures) in specific brain regions, including the bankssts (β = -0.006 mm, P = 0.016), entorhinal cortex (β = -4.856 mm2, P = 0.029), and hippocampus (β = -24.819 cm3, P = 0.045), as well as in brain regions functionally associated with visual perception, including the pericalcarine (β = -10.009 cm3, P = 0.013).

CONCLUSION

Adaptive changes and functional remodeling of brain structures occur in patients with genetically predicted HL. Brain regions functionally associated with auditory perception, visual perception, and memory function are the main brain regions vulnerable in HL.

Sensorineural Hearing Loss Affects Functional Connectivity of the Auditory Cortex, Parahippocampal Gyrus and Inferior Prefrontal Gyrus in Tinnitus Patients

Background

Tinnitus can interfere with a patient’s speech discrimination, but whether tinnitus itself or the accompanying sensorineural hearing loss (SNHL) causes this interference is still unclear. We analyzed event-related electroencephalograms (EEGs) to observe auditory-related brain function and explore the possible effects of SNHL on auditory processing in tinnitus patients.

Methods

Speech discrimination scores (SDSs) were recorded in 21 healthy control subjects, 24 tinnitus patients, 24 SNHL patients, and 27 patients with both SNHL and tinnitus. EEGs were collected under an oddball paradigm. Then, the mismatch negativity (MMN) amplitude and latency, the clustering coefficient and average path length of the whole network in the tinnitus and SNHL groups were compared with those in the control group. Additionally, we analyzed the intergroup differences in functional connectivity among the primary auditory cortex (AC), parahippocampal gyrus (PHG), and inferior frontal gyrus (IFG).

Results

SNHL patients with or without tinnitus had lower SDSs than the control subjects. Compared with control subjects, tinnitus patients with or without SNHL had decreased MMN amplitudes, and SNHL patients had longer MMN latencies. Tinnitus patients without SNHL had a smaller clustering coefficient and a longer whole-brain average path length than the control subjects. SNHL patients with or without tinnitus had a smaller clustering coefficient and a longer average path length than patients with tinnitus alone. The connectivity strength from the AC to the PHG and IFG was lower on the affected side in tinnitus patients than that in control subjects; the connectivity strength from the PHG to the IFG was also lower on the affected side in tinnitus patients than that in control subjects. However, the connectivity strength from the IFG to the AC was stronger in tinnitus patients than that in the control subjects. In SNHL patients with or without tinnitus, these changes were magnified.

Conclusion

Changes in auditory processing in tinnitus patients do not influence SDSs. Instead, SNHL might cause the activity of the AC, PHG and IFG to change, resulting in impaired speech recognition in tinnitus patients with SNHL.

Decreasing auditory input induces neurogenesis impairment in the hippocampus

Hearing loss is associated with cognitive decline and dementia risk. Sensorineural hearing loss suppresses hippocampal neurogenesis, resulting in cognitive decline. However, the underlying mechanism of impaired neurogenesis and the role of microglial activation and stress responses related to hearing loss in the hippocampus remains unknown. Using a conductive hearing loss (CHL) model, we investigated whether a decrease in sound level could induce impairment of hippocampal neurogenesis and examined the differences between unilateral CHL (uCHL) and bilateral CHL (bCHL). To establish the CHL mouse model, ears were unilaterally or bilaterally occluded for five weeks by auditory canal ligation. Although hearing thresholds were significantly increased following CHL, CHL mice exhibited no significant loss of spiral ganglion or hippocampal neurons. Hippocampal neurogenesis was significantly and equally decreased in both sides following uCHL. More severe decreases in hippocampal neurogenesis were observed in both sides in bCHL mice compared with that in uCHL mice. Furthermore, microglial invasion significantly increased following CHL. Serum cortisol levels, which indicate stress response, significantly increased following bCHL. Therefore, auditory deprivation could lead to increased microglial invasion and stress responses and might be a risk factor for hippocampal neurogenesis impairment.

Long-term administration of vitamin B12 and adenosine triphosphate for idiopathic sudden sensorineural hearing loss: a retrospective study

Background

In idiopathic sudden sensorineural hearing loss (ISSNHL), the relationship between the administration duration of vitamin B12 (vit B12) with adenosine triphosphate (ATP) and their therapeutic effect is not fully understood.

Objective

To investigate the therapeutic effect of long-term 16 (≥weeks) administration of vit B12 with ATP on the prognosis of ISSNHL patients and compare it with those of short-term (<8 weeks) and middle-term (≥8 weeks, <16 weeks) administration.

Methods

We retrospectively reviewed the medical records of 117 patients with ISSNHL treated between 2015 and 2018.

Results

The overall recovery rate was 32.5%. Initial higher hearing threshold and initial higher grade of hearing loss (HL) were associated with a poor prognosis. However, the administration duration of vit B12 and ATP did not influence the overall hearing improvement. With regard to the time course of hearing recovery, there was no significant difference in hearing recovery among the long-, middle-, and short-term administration groups until 16 weeks after treatment. However, at 16–24 weeks after initial treatment, the short-term administration group exhibited significantly lower hearing recovery than did the long-term administration groups.

Conclusions

The administration duration of vit B12 and ATP did not influence the overall hearing prognosis in ISSNHL, but long-term administration of vit B12 and ATP helped prevent the progression of HL after ISSNHL. Our results suggest that long-term administration of vit B12 and ATP is not necessarily required to treat ISSNHL patients, except for slowly progressing HL in the affected ears.

Speech discrimination impairment of the worse-hearing ear in asymmetric hearing loss

OBJECTIVE

This study aimed to compare the difference in maximum speech discrimination score (SDSmax) of the worse-hearing ear in asymmetric hearing loss (ASHL) patients with that in symmetric hearing loss (SHL) patients.

DESIGN

We retrospectively reviewed medical records of patients with suspected hearing loss (HL) who underwent audiometric examinations. Patients were divided into two groups according to the difference in air conduction (AC) threshold between the right and left ears: the SHL group and the ASHL group.

STUDY SAMPLE

Of the 102 patients (204 ears), 74 (148 ears) had SHL, and 28 had ASHL.

RESULTS

The worse-hearing ear of ASHL patients exhibited a statistically significantly higher AC threshold and lower SDSmax, compared with ears of SHL patients and better-hearing ears of ASHL patients, and SDSmax exhibited a statistically significant negative correlation with AC threshold. The SDSmax was statistically significantly lower in the worse-hearing ear of the ASHL group than in moderate to severe HL ears of the SHL group, even though these groups had comparable AC thresholds.

CONCLUSIONS

ASHL patients' worse-hearing ear exhibited a lower SDSmax than SHL patients' ears, despite a comparable AC threshold. Management of hearing impairment in ASHL patients should receive more attention.

Transient Conductive Hearing Loss Regulates Cross-Modal VGLUT Expression in the Cochlear Nucleus of C57BL/6 Mice

Auditory nerve fibers synapse onto the cochlear nucleus (CN) and are labeled using the vesicular glutamate transporter-1 (VGLUT-1), whereas non-auditory inputs are labeled using the VGLUT-2. However, the underlying regulatory mechanism of VGLUT expression in the CN remains unknown. We examined whether a sound level decrease, without primary neural damage, induces cellular and VGLUT expression change in the CN, and examined the potential for neural plasticity of the CN using unilateral conductive hearing loss models. We inserted earplugs in 8-week-old mice unilaterally for 4 weeks and subsequently removed them for another 4 weeks. Although the threshold of an auditory brainstem response significantly increased across all tested frequencies following earplug insertion, it completely recovered after earplug removal. Auditory deprivation had no significant impact on spiral ganglion and ventral CN (VCN) neurons’ survival. Conversely, although the cell size and VGLUT-1 expression in the VCN significantly decreased after earplug insertion, VGLUT-2 expression in the granule cell lamina significantly increased. These cell sizes decreased and the alterations in VGLUT-1 and -2 expression almost completely recovered at 1 month after earplug removal. Our results suggested that the cell size and VGLUT expression in the CN have a neuroplasticity capacity, which is regulated by increases and decreases in sound levels. Restoration of the sound levels might partly prevent cell size decrease and maintain VGLUT expression in the CN.