Age-related hearing impairment and frailty in Alzheimer's disease: interconnected associations and mechanisms

Digging into the intrinsic capacity concept: Can it be applied to Alzheimer's disease?

Historically, aging research has largely centered on disease pathology rather than promoting healthy aging. The World Health Organization's (WHO) policy framework (2015-2030) underscores the significance of fostering the contributions of older individuals to their families, communities, and economies. The WHO has introduced the concept of intrinsic capacity (IC) as a key metric for healthy aging, encompassing five primary domains: locomotion, vitality, sensory, cognitive, and psychological. Past AD research, constrained by methodological limitations, has focused on single outcome measures, sidelining the complexity of the disease. Our current scientific milieu, however, is primed to adopt the IC concept. This is due to three critical considerations: (I) the decline in IC is linked to neurocognitive disorders, including AD, (II) cognition, a key component of IC, is deeply affected in AD, and (III) the cognitive decline associated with AD involves multiple factors and pathophysiological pathways. Our study explores the application of the IC concept to AD patients, offering a comprehensive model that could revolutionize the disease's diagnosis and prognosis. There is a dearth of information on the biological characteristics of IC, which are a result of complex interactions within biological systems. Employing a systems biology approach, integrating omics technologies, could aid in unraveling these interactions and understanding IC from a holistic viewpoint. This comprehensive analysis of IC could be leveraged in clinical settings, equipping healthcare providers to assess AD patients' health status more effectively and devise personalized therapeutic interventions in accordance with the precision medicine paradigm. We aimed to determine whether the IC concept could be extended from older individuals to patients with AD, thereby presenting a model that could significantly enhance the diagnosis and prognosis of this disease.

Impact of Concurrent Visual and Hearing Impairment on Incident Alzheimer's Disease: The LIFE Study

Background

The prevalence of Alzheimer's disease (AD) is increasing in Japan due to population aging. The association between sensory impairment and incident AD remains unclear.

Objective

This study aimed to investigate the impact of sensory impairment on incident AD.

Methods

We analyzed residents of five municipalities participating in the Longevity Improvement & Fair Evidence (LIFE) Study. The participants comprised individuals who had newly applied for long-term care needs certification between 2017 and 2022 and had no cognitive impairment upon application or AD diagnosis within the preceding six months. Participants were classified according to sensory impairment status: visual impairment (VI), hearing impairment (HI), neither sensory impairment (NSI), and dual sensory impairment (DSI). The month succeeding the certification application was set as the index month, and the interval from that month until AD onset was assessed. Multivariable Cox proportional hazards analysis was performed to calculate the risk of AD onset according to sensory impairment status while adjusting for sex, age, dependence level, self-reliance level, and comorbidities.

Results

Among 14,186 participants, we identified 1,194 (8.4%) who developed AD over a median follow-up period of 22.6 months. VI and HI only were not associated with incident AD. However, DSI conferred a significantly higher risk (HR: 1.6, CI: 1.1-2.2, p = 0.008) of AD onset than NSI.

Conclusions

Individuals with concurrent DSI have a higher risk of developing AD than those with single or NSI. Preventing and treating sensory impairment may not only improve functional outcomes, but could also help to reduce the future risk of AD.

Adjunct Methods for Alzheimer's Disease Detection: A Review of Auditory Evoked Potentials

The auditory afferent pathway as a clinical marker of Alzheimer's disease (AD) has sparked interest in investigating the relationship between age-related hearing loss (ARHL) and AD. Given the earlier onset of ARHL compared to cognitive impairment caused by AD, there is a growing emphasis on early diagnosis and intervention to postpone or prevent the progression from ARHL to AD. In this context, auditory evoked potentials (AEPs) have emerged as a widely used objective auditory electrophysiological technique for both the clinical diagnosis and animal experimentation in ARHL due to their non-invasive and repeatable nature. This review focuses on the application of AEPs in AD detection and the auditory nerve system corresponding to different latencies of AEPs. Our objective was to establish AEPs as a systematic and non-invasive adjunct method for enhancing the diagnostic accuracy of AD. The success of AEPs in the early detection and prediction of AD in research settings underscores the need for further clinical application and study.

Cocoa Polyphenols Prevent Age-Related Hearing Loss and Frailty in an In Vivo Model

Age-related hearing loss (ARHL) impairs the quality of life in elderly persons. ARHL is associated with comorbidities, such as depression, falls, or frailty. Frailty syndrome is related to poor health outcomes in old age. ARHL is a potentially modifiable risk factor for frailty. Oxidative stress has been proposed as a key factor underlying the onset and/or development of ARHL and frailty. Cocoa has high levels of polyphenols and provides many health benefits due to its antioxidant properties. Male and female C57Bl/6J mice were randomly assigned to two study groups: animals receiving a cocoa-supplemented diet and the other receiving a standard diet. Then, at the ages of 6, 14, and 22 months, hearing and frailty were measured in all mice. Auditory steady-state responses (ASSR) threshold shifts were measured to different frequencies. The frailty score was based on the "Valencia Score" adapted to the experimental animals. The total antioxidant capacity and total polyphenols in urine samples were also measured. Significant improvements in hearing ability are observed in the cocoa groups at 6, 14, and 22 months compared to the no cocoa group. The cocoa diet significantly retards the development of frailty in mice. Cocoa increases the concentration of polyphenols excreted in the urine, which increases the total antioxidant capacity. In conclusion, cocoa, due to its antioxidant properties, leads to significant protection against ARHL and frailty.

Syntactic complexity differentially affects auditory sentence comprehension performance for individuals with age-related hearing loss

Objectives

This study examined whether older adults with hearing loss (HL) experience greater difficulties in auditory sentence comprehension compared to those with typical-hearing (TH) when the linguistic burdens of syntactic complexity were systematically manipulated by varying either the sentence type (active vs. passive) or sentence length (3- vs. 4-phrases).

Methods

A total of 22 individuals with HL and 24 controls participated in the study, completing sentence comprehension test (SCT), standardized memory assessments, and pure-tone audiometry tests. Generalized linear mixed effects models were employed to compare the effects of sentence type and length on SCT accuracy, while Pearson correlation coefficients were conducted to explore the relationships between SCT accuracy and other factors. Additionally, stepwise regression analyses were employed to identify memory-related predictors of sentence comprehension ability.

Results

Older adults with HL exhibited poorer performance on passive sentences than on active sentences compared to controls, while the sentence length was controlled. Greater difficulties on passive sentences were linked to working memory capacity, emerging as the most significant predictor for the comprehension of passive sentences among participants with HL.

Conclusion

Our findings contribute to the understanding of the linguistic-cognitive deficits linked to age-related hearing loss by demonstrating its detrimental impact on the processing of passive sentences. Cognitively healthy adults with hearing difficulties may face challenges in comprehending syntactically more complex sentences that require higher computational demands, particularly in working memory allocation.

Maintained Spatial Learning and Memory Functions in Middle-Aged α9 Nicotinic Receptor Subunit Knock-Out Mice

Age-related hearing loss is linked to cognitive impairment, but the mechanisms that relate to these conditions remain unclear. Evidence shows that the activation of medial olivocochlear (MOC) neurons delays cochlear aging and hearing loss. Consequently, the loss of MOC function may be related to cognitive impairment. The α9/α10 nicotinic receptor is the main target of cholinergic synapses between the MOC neurons and cochlear outer hair cells. Here, we explored spatial learning and memory performance in middle-aged wild-type (WT) and α9-nAChR subunit knock-out (KO) mice using the Barnes maze and measured auditory brainstem response (ABR) thresholds and the number of cochlear hair cells as a proxy of cochlear aging. Our results show non-significant spatial learning differences between WT and KO mice, but KO mice had a trend of increased latency to enter the escape box and freezing time. To test a possible reactivity to the escape box, we evaluated the novelty-induced behavior using an open field and found a tendency towards more freezing time in KO mice. There were no differences in memory, ABR threshold, or the number of cochlear hair cells. We suggest that the lack of α9-nAChR subunit alters novelty-induced behavior, but not spatial learning in middle-aged mice, by a non-cochlear mechanism.

Noise-induced auditory damage affects hippocampus causing memory deficits in a model of early age-related hearing loss

Several studies identified noise-induced hearing loss (NIHL) as a risk factor for sensory aging and cognitive decline processes, including neurodegenerative diseases, such as dementia and age-related hearing loss (ARHL). Although the association between noise- and age-induced hearing impairment has been widely documented by epidemiological and experimental studies, the molecular mechanisms underlying this association are not fully understood as it is not known how these risk factors (aging and noise) can interact, affecting memory processes. We recently found that early noise exposure in an established animal model of ARHL (C57BL/6 mice) accelerates the onset of age-related cochlear dysfunctions. Here, we extended our previous data by investigating what happens in central brain structures (auditory cortex and hippocampus), to assess the relationship between hearing and memory impairment and the possible combined effect of noise and sensory aging on the cognitive domain. To this aim, we exposed juvenile C57BL/6 mice of 2 months of age to repeated noise sessions (60 min/day, pure tone of 100 dB SPL, 10 kHz, 10 consecutive days) and we monitored auditory threshold by measuring auditory brainstem responses (ABR), spatial working memory, by using the Y-maze test, and basal synaptic transmission by using ex vivo electrophysiological recordings, at different time points (1, 4 and 7 months after the onset of noise exposure, corresponding to 3, 6 and 9 months of age). We found that hearing loss, along with accelerated presbycusis onset, can induce persistent synaptic alterations in the auditory cortex. This was associated with decreased memory performance and oxidative-inflammatory injury in the hippocampus, the extra-auditory structure involved in memory processes. Collectively, our data confirm the critical relationship between auditory and memory circuits, suggesting that the combined detrimental effect of noise and sensory aging on hearing function can be considered a high-risk factor for both sensory and cognitive degenerative processes, given that early noise exposure accelerates presbycusis phenotype and induces hippocampal-dependent memory dysfunctions.

Vulnerability to chronic stress and the phenotypic heterogeneity of presbycusis with subjective tinnitus

Age-related functional reserve decline and vulnerability of multiple physiological systems and organs, as well as at the cellular and molecular levels, result in different frailty phenotypes, such as physical, cognitive, and psychosocial frailty, and multiple comorbidities, including age-related hearing loss (ARHL) and/or tinnitus due to the decline in auditory reserve. However, the contributions of chronic non-audiogenic cumulative exposure, and chronic audiogenic stress to phenotypic heterogeneity of presbycusis and/or tinnitus remain elusive. Because of the cumulative environmental stressors throughout life, allostasis systems, the hypothalamus-pituitary-adrenal (HPA) and the sympathetic adrenal-medullary (SAM) axes become dysregulated and less able to maintain homeostasis, which leads to allostatic load and maladaptation. Brain-body communication via the neuroendocrine system promotes systemic chronic inflammation, overmobilization of energetic substances (glucose and lipids), and neuroplastic changes via the non-genomic and genomic actions of glucocorticoids, catecholamines, and their receptors. These systemic maladaptive alterations might lead to different frailty phenotypes and physical, cognitive, and psychological comorbidities, which, in turn, cause and exacerbate ARHL and/or tinnitus with phenotypic heterogeneity. Chronic audiogenic stressors, including aging accompanying ontological diseases, cumulative noise exposure, and ototoxic drugs as well as tinnitus, activate the HPA axis and SAM directly and indirectly by the amygdala, promoting allostatic load and maladaptive neuroplasticity in the auditory system and other vulnerable brain regions, such as the hippocampus, amygdala, and medial prefrontal cortex (mPFC). In the auditory system, peripheral deafferentation, central disinhibition, and tonotopic map reorganization may trigger tinnitus. Cross-modal maladaptive neuroplasticity between the auditory and other sensory systems is involved in tinnitus modulation. Persistent dendritic growth and formation, reduction in GABAergic inhibitory synaptic inputs induced by chronic audiogenic stresses in the amygdala, and increased dendritic atrophy in the hippocampus and mPFC, might involve the enhancement of attentional processing and long-term memory storage of chronic subjective tinnitus, accompanied by cognitive impairments and emotional comorbidities. Therefore, presbycusis and tinnitus are multisystem disorders with phenotypic heterogeneity. Stressors play a critical role in the phenotypic heterogeneity of presbycusis. Differential diagnosis based on biomarkers of metabonomics study, and interventions tailored to different ARHL phenotypes and/or tinnitus will contribute to healthy aging and improvement in the quality of life.

Dietary Characteristics of Elders with Frailty and with Mild Cognitive Impairment: Cross-Sectional Findings and Implications from the Nutrition and Health Survey in Taiwan 2014-2017

It is unclear whether low dietary intake accompanied with multiple nutrient deficiencies or specific nutrient inadequacy is associated with geriatric syndrome. This study aimed to examine the nutrition inadequacy profiles associated with frailty and cognitive impairment (CI). With information from the Nutrition and Health Survey in Taiwan, 2014-2017, sex-specific nutrient intakes and intake per kg of body weight (BW) were estimated from 24-hour recall data for two age groups (65-74 years; ≥75 years) regarding the three frailty and three CI subgroups. Total energy intakes were significantly lower with the severity of both frailty and CI in analysis combining both gender and age groups, and in both the 65-to-74-year-old women or the over-75-year-old women. These trends were observed but not significant in either of the two age groups in men. Significantly lower levels of energy intake have been observed when age, sex, and sampling strata were adjusted. Intake levels of multiple nutrients also decreased with the severity of frailty and CI. A greater number of nutrient inadequacies for the frail and the CI was found in the 65-to-74-year-old group than the over-75-year-old age group. However, most of the associations between micronutrients and the two geriatric syndromes disappeared after energy adjustment. The remaining few did not show consistency across age-sex subgroups. In conclusion, frailty or CI was associated with low amounts of food consumption accompanied by multiple nutrient insufficiencies. Dietary intervention to ensure adequate total energy and multiple nutrient intakes should be trialed in the geriatric population to address both the causal and efficacy issues.

Sensory and motor correlates of frailty: dissociation between frailty phenotype and frailty index

Background

Frailty has been associated with a decline in sensory and motor function. However, given that different frailty measures were shown to overlap but also differ in their diagnostic properties, sensory and motor correlates of frailty might be different depending on the operationalization of frailty. Our objective was to identify sensory and motor determinants of frailty and compare the results between frailty phenotype (FP) and frailty index (FI).

Methods

Data from 44 pre-frail and frail subjects aged 65 and above were used. Frailty was measured using the FP and the FI. Sensory function in the visual, auditory, and tactile domain was assessed using visual acuity, absolute hearing threshold and mechanical detection threshold. Upper extremity motor performance was evaluated by the Purdue Pegboard Test and the Short Physical Performance Battery was used to assess lower extremity motor function. Multiple logistic regression models were employed to determine associations of sensory and motor function with frailty vs. pre-frailty for both frailty measures.

Results

The frailty measures were moderately correlated (0.497, p ≤ 0.01) and had a Kappa agreement of 0.467 (p = 0.002). Using the FP, frailty was significantly associated with reduced upper extremity motor function only (OR = 0.50, 95% CI 0.29–0.87, p = 0.014). Frailty as assessed by the FI was significantly related to higher hearing thresholds (OR = 1.21, 95% CI 1.02–1.43, p = 0.027) and reduced lower extremity performance (OR = 0.32, 95% CI 0.13–0.77, p = 0.012).

Conclusion

Frailty is related to reduced performance in measures of sensory and motor function. However, traditional measures of frailty might be differentially sensitive to capture sensory and motor decline, possibly contributing to the much-observed discordance between the diagnostic instruments. This should be taken into account by researchers and clinicians when planning and evaluating therapeutic interventions for frailty.

Trial registration

ClinicalTrials.gov NCT03666039. Registered 11 September 2018 – Retrospectively registered.

The Association Between Hearing Impairment, Vision Impairment, Dual Sensory Impairment, and Serious Cognitive Impairment: Findings from a Population-Based Study of 5.4 million Older Adults

Background:

Sensory impairments and cognitive impairment are increasing in scope due to the aging population.

Objective:

To investigate the association between hearing impairment, vision impairment, and dual sensory impairment with cognitive impairment among older adults.

Methods:

Secondary analysis of a combination of ten consecutive waves (2008–2017) of the nationally representative American Community Survey. The sample included 5.4 million community-dwelling and institutionalized older adults aged 65 and older. Bivariate and logistic regression models were conducted to examine the association hearing impairment, vision impairment, and dual sensory impairment with cognitive impairment.

Results:

After controlling for age, race, education, and income, older adults with only hearing impairment had more than double the odds of cognitive impairment (OR = 2.66, 95% CI = 2.64, 2.68), while older adults with only vision impairment had more than triple the odds of cognitive impairment (OR = 3.63; 95% CI = 3.59, 3.67). For older adults with dual sensory impairment, the odds of cognitive impairment were eight-fold (OR = 8.16; 95% CI = 8.07, 8.25). Similar trends were apparent in each sex and age cohort.

Conclusion:

Hearing and vision impairment are both independently associated with cognitive impairment. However, dual sensory impairment is associated with substantially higher odds of cognitive impairment, even after controlling for sociodemographic characteristics. Practitioners working with older adults may consider treatment for sensory impairments and cognitive impairment concurrently. Future research is needed to determine if the association is causal, and to investigate the effectiveness of common methods of treatment for sensory impairment for reducing the prevalence of cognitive impairment.

Downregulation of REST in the cochlea contributes to age-related hearing loss via the p53 apoptosis pathway

Age-related hearing loss (AHL) is the most common sensory disorder amongst the elderly population. Although the degeneration of spiral ganglion neurons (SGNs) and hair cells (HCs) is considered to play a critical role in AHL, the mechanism has not been fully outlined. The repressor element 1-silencing transcription factor (REST) has recently been associated with mediating cell death in neurodegenerative diseases. However, whether REST induces degeneration of cochlear HCs and SGNs to contribute to AHL remains unknown. Here, we report that REST expression was decreased in HCs and SGNs in AHL mice. Conditional deletion of Rest in HCs and SGNs of 2-month-old mice resulted in hearing loss accompanied by the upregulation of p53, TNFR1(tumor necrosis factor receptor-1), and cleaved caspase-3. The p53 inhibitor pifithrin-α significantly attenuated SGN and HC damage and rescued hearing impairment in Rest cKO mice. Furthermore, downregulation of REST by H₂O₂ treatment induced apoptosis in the House Ear Institute Organ of Corti 1 cell, through the upregulation of p53. In contrast, overexpression of REST reversed the changes in p53 expression. In addition, REST was further shown to bind directly to the p53 promoter site, thereby inhibiting the effect of p53. Finally, in aged mice, the p53 inhibitor significantly reduced loss of HCs and SGNs, and subsequently improved hearing. In summary, our findings indicate that REST has a protective role in AHL, and that its deficiency upregulates p53 and induces cochlear cell apoptosis, which that leads to deafness.

Hearing Loss and Cognition: What We Know and Where We Need to Go

Although a causal association remains to be determined, epidemiologic evidence suggests an association between hearing loss and increased risk of dementia. If we determine the association is causal, opportunity for targeted intervention for hearing loss may play a fundamental role in dementia prevention. In this discussion, we summarize current research on the association between hearing loss and dementia and review potential casual mechanisms behind the association (e.g., sensory-deprivation hypothesis, information-degradation hypothesis, common cause). We emphasize key areas of research which might best inform our investigation of this potential casual association. These selected research priorities include examination of the causal mechanism, measurement of co-existing hearing loss and cognitive impairment and determination of any bias in testing, potential for managing hearing loss for prevention of dementia and cognitive decline, or the potential to reduce dementia-related symptoms through the management of hearing loss. Addressing these research gaps and how results are then translated for clinical use may prove paramount for dementia prevention, management, and overall health of older adults.

Frailty Syndrome and Oxidative Stress as Possible Links Between Age-Related Hearing Loss and Alzheimer’s Disease

As it is well known, a worldwide improvement in life expectancy has taken place. This has brought an increase in chronic pathologies associated with aging. Cardiovascular, musculoskeletal, psychiatric, and neurodegenerative conditions are common in elderly subjects. As far as neurodegenerative diseases are concerned dementias and particularly, Alzheimer’s disease (AD) occupy a central epidemiological position given their high prevalence and their profound negative impact on the quality of life and life expectancy. The amyloid cascade hypothesis partly explains the immediate cause of AD. However, limited therapeutical success based on this hypothesis suggests more complex remote mechanisms underlying its genesis and development. For instance, the strong association of AD with another irreversible neurodegenerative pathology, without curative treatment and complex etiology such as presbycusis, reaffirms the intricate nature of the etiopathogenesis of AD. Recently, oxidative stress and frailty syndrome have been proposed, independently, as key factors underlying the onset and/or development of AD and presbycusis. Therefore, the present review summarizes recent findings about the etiology of the above-mentioned neurodegenerative diseases, providing a critical view of the possible interplay among oxidative stress, frailty syndrome, AD and presbycusis, that may help to unravel the common mechanisms shared by both pathologies. This knowledge would help to design new possible therapeutic strategies that in turn, will improve the quality of life of these patients.

Association between Late-Onset Ménière's Disease and the Risk of Incident All-Cause Dementia

Studies reported an association between impaired hearing and vestibular function with the risk of dementia. This study investigated the association between Ménière’s disease (MD) and the risk of dementia using a nationwide cohort sample of data obtained from the South Korea National Health Insurance Service. The MD group (n = 496) included patients aged over 55 years and diagnosed between 2003 and 2006. The comparison group was selected using propensity score matching (n = 1984). Cox proportional hazards regression models were used to calculate incidence and hazard ratios for dementia events. The incidence of dementia was 14.3 per 1000 person–years in the MD group. After adjustment for certain variables, the incidence of dementia was higher in the MD group than in the comparison group (adjusted hazard ratio (HR) = 1.57, 95% confidence interval = 1.17–2.12). Subgroup analysis showed a significantly increased adjusted HR for developing Alzheimer’s disease (1.69, 95% confidence interval = 1.20–2.37) and vascular dementia (1.99, 95% confidence interval = 1.10–3.57) in the MD group. Patients with dementia experienced a higher frequency of MD episodes than those without dementia. Our findings suggest that late-onset MD is associated with an increased incidence of all-cause dementia, and it might be used as a basis for an earlier diagnosis of dementia.

Assessing a Sensory-Motor-Cognition Triad in Amnestic Mild Cognitive Impairment With Dichotic Listening While Walking: A Dual-Task Paradigm

A contemporary topic in aging research relates to the significance of cognitive changes proper to mild cognitive impairment (MCI) to higher risk of falls and gait deteriorations. The present study addresses this question in the amnestic type of MCI (aMCI) by examining a triad of interrelated comorbidities occurring in the MCI condition: attentional impairments, hearing loss and gait disturbances. To this end, we applied a dichotic listening (DL) test during over-ground walking. DL assesses spontaneous and lateralized auditory attention in three conditions (i.e., free report or Non-forced (NF), Forced-Right (FR) ear and Forced-Left (FL) ear). Earlier reports suggest that this dual-task paradigm evoke asymmetric gait effects on healthy controls, which are moderated by degree of hearing loss. Therefore, the aim of the present study was to evaluate the effects of DL on bilateral (data from both limbs) and lateralized (each limb separately) gait outcomes in a group of forty-three aMCI participants (mean = 71.19) and fifty-two healthy older controls (mean = 70.90) by using hearing loss as a covariate in all analyses. Results showed the aMCI group presented overall compromised gait parameters, especially higher gait variability in all DL conditions during lateralized attentional control. These findings were observed bilaterally, and no lateralized effects on gait were observed. Only after controlling for hearing acuity, gait asymmetries on step length variability emerged almost exclusively in healthy controls. It was concluded that hearing loss in the aMCI group together with higher attentional impairments preclude aMCI individuals to properly execute DL and therefore, they do not display gait asymmetries. The present data demonstrate that varied demands on attentional control dependent on hearing acuity affects gait negatively in healthy older adults and aMCI individuals in very different ways. The appearance of asymmetric effects seems to be a perturbation related to normal aging, while the lack of asymmetries but exaggerated gait variability characterizes aMCI. The present findings show the intricate interplay of sensory, cognitive, and motor deteriorations in different group of older adults, which stresses the need of addressing co-occurring comorbidities behind gait perturbations in individuals prone to develop a dementia state.

The Auditory Afferent Pathway as a Clinical Marker of Alzheimer's Disease

Brain stem neural tracts and nuclei may be disturbed prior to observable neuronal atrophy in AD. In this perspective, we discuss the notion of functional deficits presenting prior to structural abnormalities in Alzheimer's disease (AD). Imaging of inferior colliculi using magnetic resonance spectroscopy (MRS) shows significant decrease in the neuronal markers, N acetyl aspartate/creatine ratio and increase in the glial marker myo-Inositol, in subjects with Mini-Mental State Examination scores greater than 24 and with no signs of atrophy in their MRI of the medial temporal lobe. Abnormalities in components of the auditory event-related potentials (ERPs) are described in cognitive impairment including AD. We observed a significant decrease in amplitude and increase in latency during the first 10 ms of auditory evoked potentials measured on electroencephalography (EEG) indicating slow auditory response of the brainstem. EEG spectral power recorded at the cortex is also associated with neural activity at the level of the inferior colliculi. We postulate that a functional examination of auditory afferent pathways, using non-invasive techniques, such as MRS, brain stem auditory evoked potentials (BAEPs) and ERPs may improve diagnostic accuracy of AD. Functional changes precede structural changes and it is important to further understand the relationship between biochemical and electrophysiological measures such as MRS, BAEPs and EEG.

Hearing Loss and Cognitive Impairment: Epidemiology, Common Pathophysiological Findings, and Treatment Considerations

In recent years, there has been increasing research interest in the correlation between hearing impairment and cognitive decline, two conditions that have demonstrated a strong association. Hearing loss appears as a risk factor for cognitive impairment, especially among certain populations, notably nursing home residents. Furthermore, hearing loss has been identified as a modifiable age-related condition linked to dementia, and it has been estimated that midlife hearing loss, if eliminated, might decrease the risk of dementia in the general population. Several mechanisms have been suggested to explain the pathologic connections between hearing loss and dementia; however, clear evidence is missing, and the common pathophysiological basis is still unclear. In this review, we discussed current knowledge about the relationship between hearing loss and dementia, and future perspectives in terms of the effects of hearing rehabilitation for early prevention of cognitive decline.

Cogmed Training Does Not Generalize to Real-World Benefits for Adult Hearing Aid Users: Results of a Blinded, Active-Controlled Randomized Trial

Objectives:

Performance on working memory tasks is positively associated with speech-in-noise perception performance, particularly where auditory inputs are degraded. It is suggested that interventions designed to improve working memory capacity may improve domain-general working memory performance for people with hearing loss, to benefit their real-world listening. We examined whether a 5-week training program that primarily targets the storage component of working memory (Cogmed RM, adaptive) could improve cognition, speech-in-noise perception and self-reported hearing in a randomized controlled trial of adult hearing aid users with mild to moderate hearing loss, compared with an active control (Cogmed RM, nonadaptive) group of adults from the same population.

Design:

A preregistered randomized controlled trial of 57 adult hearing aid users (n = 27 experimental, n = 30 active control), recruited from a dedicated database of research volunteers, examined on-task learning and generalized improvements in measures of trained and untrained cognition, untrained speech-in-noise perception and self-reported hearing abilities, pre- to post-training. Participants and the outcome assessor were both blinded to intervention allocation. Retention of training-related improvements was examined at a 6-month follow-up assessment.

Results:

Per-protocol analyses showed improvements in trained tasks (Cogmed Index Improvement) that transferred to improvements in a trained working memory task tested outside of the training software (Backward Digit Span) and a small improvement in self-reported hearing ability (Glasgow Hearing Aid Benefit Profile, Initial Disability subscale). Both of these improvements were maintained 6-month post-training. There was no transfer of learning shown to untrained measures of cognition (working memory or attention), speech-in-noise perception, or self-reported hearing in everyday life. An assessment of individual differences showed that participants with better baseline working memory performance achieved greater learning on the trained tasks. Post-training performance for untrained outcomes was largely predicted by individuals’ pretraining performance on those measures.

Conclusions:

Despite significant on-task learning, generalized improvements of working memory training in this trial were limited to (a) improvements for a trained working memory task tested outside of the training software and (b) a small improvement in self-reported hearing ability for those in the experimental group, compared with active controls. We found no evidence to suggest that training which primarily targets storage aspects of working memory can result in domain-general improvements that benefit everyday communication for adult hearing aid users. These findings are consistent with a significant body of evidence showing that Cogmed training only improves performance for tasks that resemble Cogmed training. Future research should focus on the benefits of interventions that enhance cognition in the context in which it is employed within everyday communication, such as training that targets dynamic aspects of cognitive control important for successful speech-in-noise perception.

Self-reported hearing difficulty increases 3-year risk of incident cognitive impairment: The role of leisure activities and psychological resilience

OBJECTIVE

Although hearing difficulty is associated with cognitive impairment, little is known about the potential mechanisms involved. This study assessed the mediating effects of leisure activities and psychological resilience on the association between hearing difficulty and cognitive impairment.

METHODS

Two waves of Chinese Longitudinal Healthy Longevity Survey (2011-2014) were used in the current analysis. Hearing difficulty, leisure activities and psychological resilience were measured at baseline. Cognitive function was assessed using the Chinese version of the Mini-Mental State Examination. The data were analyzed using generalized structural equation modeling with adjustment for confounding factors.

RESULTS

Of the 4267 participants at baseline, 33.5% (1430) reported hearing difficulty. The incidence of cognitive impairment was 15.3% (651) during the 3-year follow-up. Hearing difficulty increased the risk of cognitive impairment (odds ratio [OR] = 1.59, 95% confidence intervals [CI]: 1.26-1.92). Leisure activities and psychological resilience partly mediated the association between hearing difficulty and cognitive impairment. Hearing difficulty was negatively related to leisure activities (β = -0.23, 95% CI: -0.41 to -0.05) and psychological resilience (β = -0.34, 95% CI: -0.57 to -0.11). Furthermore, leisure activities (OR = 0.92, 95% CI: 0.89-0.96) and psychological resilience (OR = 0.95, 95% CI: 0.93-0.98) would significantly decrease the risk of cognitive impairment.

CONCLUSIONS

Hearing difficulty was associated with the incidence of cognitive impairment in older adults. Leisure activities and psychological resilience mediated the relationship. Participation in leisure activity and promoting psychological resilience may be candidate interventions in preventing cognitive impairment among the individuals with hearing difficulty.

Hearing difficulty is linked to Alzheimer's disease by common genetic vulnerability, not shared genetic architecture

Age-related hearing loss was recently established as the largest modifiable risk factor for Alzheimer's disease (AD), however, the reasons for this link remain unclear. We investigate shared underlying genetic associations using results from recent large genome-wide association studies (GWAS) on adult hearing difficulty and AD. Genetic correlation and Mendelian randomization (MR) analysis do not support a genetic correlation between the disorders, but suggest a direct causal link from AD genetic risk to hearing difficulty, driven by APOE. Systematic MR analyses on the effect of other traits revealed shared effects of glutamine, gamma-glutamylglutamine, and citrate levels on reduced risk of both hearing difficulty and AD. In addition, pathway analysis on GWAS risk variants suggests shared function in neuronal signalling pathways as well as etiology of diabetes and cardiovascular disease. However, after multiple testing corrections, neither analysis led to statistically significant associations. Altogether, our genetic-driven analysis suggests hearing difficulty and AD are linked by a shared vulnerability in molecular pathways rather than by a shared genetic architecture.

Brain Frequency-Specific Changes in the Spontaneous Neural Activity Are Associated With Cognitive Impairment in Patients With Presbycusis

Presbycusis (PC) is characterized by preferential hearing loss at high frequencies and difficulty in speech recognition in noisy environments. Previous studies have linked PC to cognitive impairment, accelerated cognitive decline and incident Alzheimer’s disease. However, the neural mechanisms of cognitive impairment in patients with PC remain unclear. Although resting-state functional magnetic resonance imaging (rs-fMRI) studies have explored low-frequency oscillation (LFO) connectivity or amplitude of PC-related neural activity, it remains unclear whether the abnormalities occur within all frequency bands or within specific frequency bands. Fifty-one PC patients and fifty-one well-matched normal hearing controls participated in this study. The LFO amplitudes were investigated using the amplitude of low-frequency fluctuation (ALFF) at different frequency bands (slow-4 and slow-5). PC patients showed abnormal LFO amplitudes in the Heschl’s gyrus, dorsolateral prefrontal cortex (dlPFC), frontal eye field and key nodes of the speech network exclusively in slow-4, which suggested that abnormal spontaneous neural activity in PC was frequency dependent. Our findings also revealed that stronger functional connectivity between the dlPFC and the posterodorsal stream of auditory processing, as well as lower functional coupling between the PCC and key nodes of the DMN, which were associated with cognitive impairments in PC patients. Our study might underlie the cross-modal plasticity and higher-order cognitive participation of the auditory cortex after partial hearing deprivation. Our findings indicate that frequency-specific analysis of ALFF could provide valuable insights into functional alterations in the auditory cortex and non-auditory regions involved in cognitive impairment associated with PC.

Hearing Impairment and Cognition in an Aging World

With the increasing number of older adults around the world, the overall number of dementia cases is expected to rise dramatically in the next 40 years. In 2020, nearly 6 million individuals in the USA were living with Alzheimer's disease, the most common type of dementia, with anticipated growth to nearly 14 million by year 2050. This increasing prevalence, coupled with high societal burden, makes prevention and intervention of dementia a medical and public health priority. As clinicians and researchers, we will continue to see more individuals with hearing loss with other comorbidities including dementia. Epidemiologic evidence suggests an association between hearing loss and increased risk of dementia, presenting opportunity for targeted intervention for hearing loss to play a fundamental role in dementia prevention. In this discussion, we summarize current research on the association between hearing loss and dementia and review potential casual mechanisms behind the association (e.g., sensory-deprivation hypothesis, information-degradation hypothesis, common cause). We emphasize key areas of research which might best inform our investigation of this potential casual association. These selected research priorities include examination of the causal mechanism, measurement of co-existing hearing loss and cognitive impairment, and potential of aural rehabilitation. Addressing these research gaps and how results are then translated for clinical use is paramount for dementia prevention and overall health of older adults.

The Impact of Hearing Loss on Clinical Dementia and Preclinical Cognitive Impairment in Later Life

BACKGROUND

Dementia and cognitive impairment were significantly associated with hearing loss. The impact of hearing loss on dementia and cognitive impairment is understudied, particularly for different effect on cognitive impairment according to types of hearing loss.

OBJECTIVE

The present study was conducted to elucidate the association between clinically diagnosed dementia and hearing loss with consideration of the type of hearing loss among an elderly population, and to explore the effects of different types of hearing loss on preclinical cognitive impairment.

METHODS

Data (n = 59,675) from the Korean National Health Insurance Service-Health Screening were used to calculate odds ratios (OR) for cognitive impairment according to type of hearing loss (conductive, sensorineural, mixed, and noise-induced hearing losses, and presbycusis). Cognitive impairment was assessed using the Korean Dementia Screening Questionnaire-Prescreening (KDSQ-P).

RESULTS

Cognitive impairment was significantly associated with conductive (OR: 1.45, 95% confidence interval (CI): 1.20-1.77), sensorineural (OR: 1.23, CI: 1.12-1.36), and noise-induced hearing loss (OR: 1.32, CI: 1.12-1.56), and presbycusis (OR: 1.53, CI: 1.25-1.87). Among participants scoring positive on the KDSQ-P (score≥4), the KDSQ-P score was significantly elevated in the mixed and noise-induced hearing loss groups.

CONCLUSION

This study revealed a significant correlation between different types of hearing loss and cognitive impairment. Noise-induced hearing loss is especially important because it occurs earlier than other types of hearing loss and has large effects on cognitive impairment.

Association between Cav3 channel upregulation in spiral ganglion neurons and age-dependent hearing loss

Ca_v3 channels play a critical role in maintaining calcium homeostasis, and its dysregulation is related to age-related diseases, such as age-related hearing loss (AHL). However, the underlying mechanism of the Ca_v3 channels involved in AHL remains unknown. Previous studies have shown that the degeneration of spiral ganglion neurons (SGNs) plays a critical role in AHL. Here, we explored the involvement of Ca_v3 channels in the dysregulation of SGNs in AHL. We used C57BL/6 mice as the AHL mouse model and found that the expression of Ca_v3 channels was increased in SGNs associated with age. The three subtypes of Ca_v3 channels were present in the apical, middle, and basal SGNs from young and older (AHL) mice. The immunostaining data suggest that Ca_v3.1 and Ca_v3.2 may contribute to Ca_v3 upregulation in SGNs of AHL mice. Additionally, we found that calpain-2 and apoptosis-inducing factor (AIF) were activated in SGNs from AHL mice. The inhibition of Ca_v3 channels or calpain-2 reduced AIF-activation in SGNs may affect neuronal survival. In conclusion, the findings suggest that Ca_v3 channels are upregulated in SGNs from AHL mice that may contribute to the degeneration of SGNs through the calpain-2-AIF apoptosis pathway in AHL mice.

Leisure activities and psychological wellbeing reduce the risk of cognitive impairment among older adults with hearing difficulty: A longitudinal study in China

OBJECTIVES

. We used longitudinal cohort data to examine the effect of leisure activities and psychological wellbeing on the risk of cognitive impairment among Chinese older adults with hearing difficulty (HD).

STUDY DESIGN

. This prospective cohort study included 10,341 cognitively normal individuals aged 65 years or more at baseline from the Chinese Longitudinal Healthy Longevity survey (from 2002 to 2011).

MAIN OUTCOME MEASURES

. Hearing difficulty, leisure activities and psychological wellbeing were measured at baseline. Cognitive function was assessed using the Chinese version of the Mini-Mental State Examination (MMSE). Cognitive impairment was defined as an MMSE score of less than 18 points.

RESULTS

. During a median follow-up of 5.6 years (59,869 person-years), 2,614 participants developed cognitive impairment. Cox proportional hazards models showed that the multi-adjusted hazard ratio (HR, 95% confidence interval) of cognitive impairment was 1.42 (1.28-1.58) for HD. Participants with a healthy lifestyle had a lower risk of cognitive impairment (HR = 0.77, 95% CI 0.69-0.85). Furthermore, participants with HD and a healthy lifestyle (HR = 1.67, 95% CI 1.27-2.18) had a lower HR of cognitive impairment than those with HD and an unhealthy lifestyle (HR = 1.86, 95% CI 1.61-2.14). A healthy lifestyle also delayed the onset of cognitive impairment by 0.50 years in people with HD.

CONCLUSIONS

. HD was associated with an increased risk of cognitive impairment, but a healthy lifestyle may decrease the risk of cognitive impairment related to HD and delay the onset of cognitive impairment.

Hearing and dementia: from ears to brain

The association between hearing impairment and dementia has emerged as a major public health challenge, with significant opportunities for earlier diagnosis, treatment and prevention. However, the nature of this association has not been defined. We hear with our brains, particularly within the complex soundscapes of everyday life: neurodegenerative pathologies target the auditory brain, and are therefore predicted to damage hearing function early and profoundly. Here we present evidence for this proposition, based on structural and functional features of auditory brain organization that confer vulnerability to neurodegeneration, the extensive, reciprocal interplay between 'peripheral' and 'central' hearing dysfunction, and recently characterized auditory signatures of canonical neurodegenerative dementias (Alzheimer's disease, Lewy body disease and frontotemporal dementia). Moving beyond any simple dichotomy of ear and brain, we argue for a reappraisal of the role of auditory cognitive dysfunction and the critical coupling of brain to peripheral organs of hearing in the dementias. We call for a clinical assessment of real-world hearing in these diseases that moves beyond pure tone perception to the development of novel auditory 'cognitive stress tests' and proximity markers for the early diagnosis of dementia and management strategies that harness retained auditory plasticity.

Heterogeneous Influence of Frailty Phenotypes in Age-Related Hearing Loss and Tinnitus in Chinese Older Adults: An Explorative Study

Background

Fried physical frailty, with mobility frailty and non-motor frailty phenotypes, is a heterogeneous syndrome. The coexistence of the two phenotypes and cognitive impairment is referred to as cognitive frailty (CF). It remains unknown whether frailty phenotype has a different association with hearing loss (HL) and tinnitus.

Methods

Of the 5,328 community-dwelling older adults, 429 participants aged ≥58 years were enrolled in the study. The participants were divided into robust, mobility, and non-mobility frailty, mobility and non-mobility CF (subdivided into reversible and potentially reversible CF, RCF, and PRCF), and cognitive decline [subdivided into mild cognitive impairment (MCI) and pre-MCI] groups. The severity and presentations of HL and/or tinnitus were used as dependent variables in the multivariate logistic or nominal regression analyses with forward elimination adjusted for frailty phenotype stratifications and other covariates.

Results

Patients with physical frailty (mobility frailty) or who are robust were found to have lower probability of developing severe HL and tinnitus, and presented HL and/or tinnitus than those with only cognitive decline, or CF. Patients with RCF and non-mobility RCF had higher probability with less HL and tinnitus, and the presentation of HL and/or tinnitus than those with PRCF and mobility RCF. Other confounders, age, cognitive and social function, cardiovascular disease, depression, and body mass index, independently mediated the severity of HL and tinnitus, and presented HL and/or tinnitus.

Conclusion

Frailty phenotypes have divergent association with HL and tinnitus. Further research is required to understand the differential mechanisms and the personalized intervention of HL and tinnitus.

Clinical Trial Registration

ClinicalTrials.gov identifier, NCT2017K020.

Mild behavioral impairment is related to frailty in non-dementia older adults: a cross-sectional study

BACKGROUND

Frailty and cognitive decline are highly prevalent among older adults. However, the relationship between frailty and mild behavioral impairment (MBI), a dementia risk syndrome characterized by later-life emergence of persistent neuropsychiatric symptoms, has yet to be elucidated. We aimed to evaluate the associations between MBI and frailty in older adults without dementia.

METHODS

In this cross-sectional study, a consecutive series of 137 older adults without dementia in the Anti-Aging Study, recruited from primary care clinics, were enrolled. Frailty was estimated using the Fried phenotype. MBI was evaluated by the Mild Behavioral Impairment Checklist (MBI-C) at a cut-off point of > 8. Cognition was assessed with the Chinese versions of the Montreal Cognitive Assessment (MoCA-BC) and Mini-mental State Examination (MMSE). Multivariable logistic regression was performed to estimate the relationship between MBI and objective cognition with frailty status.

RESULTS

At baseline, 30.7% of the older adults had frailty and 18.2% had MBI (MBI+ status). Multivariable logistic regression analysis demonstrated that compared to those without MBI (MBI- status), MBI+ was more likely to have frailty (odds ratio [OR] = 7.44, 95% CI = 1.49-37.21, p = 0.02). Frailty and MBI were both significantly associated with both MMSE and MoCA-BC score (p < 0.05).

CONCLUSIONS

Both frailty and MBI status were associated with higher odds of cognitive impairment. MBI was significantly associated with an increased risk of having frailty in the absence of dementia. This association merits further study to identify potential strategies for the early detection, prevention and therapeutic intervention of frailty.

Hearing aids to support cognitive functions of older adults at risk of dementia: the HearCog trial- clinical protocols

Background

Globally, about 50 million people were living with dementia in 2015, with this number projected to triple by 2050. With no cure or effective treatment currently insight, it is vital that factors are identified which will help prevent or delay both age-related and pathological cognitive decline and dementia. Observational data have suggested that hearing loss is a potentially modifiable risk factor for dementia, but no conclusive evidence from randomised controlled trials is currently available.

Methods

The HearCog trial is a 24-month, randomised, controlled clinical trial aimed at determining whether a hearing loss intervention can delay or arrest the cognitive decline. We will randomise 180 older adults with hearing loss and mild cognitive impairment to a hearing aid or control group to determine if the fitting of hearing aids decreases the 12-month rate of cognitive decline compared with the control group. In addition, we will also determine if the expected clinical gains achieved after 12 months can be sustained over an additional 12 months and if losses experienced through the non-correction of hearing loss can be reversed with the fitting of hearing aids after 12 months.

Discussion

The trial will also explore the cost-effectiveness of the intervention compared to the control arm and the impact of hearing aids on anxiety, depression, physical health and quality of life. The results of this trial will clarify whether the systematic correction of hearing loss benefits cognition in older adults at risk of cognitive decline. We anticipate that our findings will have implications for clinical practice and health policy development.

Trial registration

Australian and New Zealand Clinical Trials Registry (ANZCTR: 12618001278224), registered on 30.07.2018.

Grip Strength, Neurocognition, and Social Functioning in People WithType-2 Diabetes Mellitus, Major Depressive Disorder, Bipolar Disorder, and Schizophrenia

BACKGROUND

Frailty is a common syndrome among older adults and patients with several comorbidities. Grip strength (GS) is a representative parameter of frailty because it is a valid indicator of current and long-term physical conditions in the general population and patients with severe mental illnesses (SMIs). Physical and cognitive capacities of people with SMIs are usually impaired; however, their relationship with frailty or social functioning have not been studied to date. The current study aimed to determine if GS is a valid predictor of changes in cognitive performance and social functioning in patients with type-2 diabetes mellitus and SMIs.

METHODS

Assessments of social functioning, cognitive performance, and GS (measured with an electronic dynamometer) were conducted in 30 outpatients with type 2 diabetes mellitus, 35 with major depressive disorder, 42 with bipolar disorder, 30 with schizophrenia, and 28 healthy controls, twice during 1-year, follow-up period. Descriptive analyses were conducted using a one-way analysis of variance for continuous variables and the chi-squared test for categorical variables. Differences between groups for the motor, cognitive, and social variables at T1 and T2 were assessed using a one-way analysis of covariance, with sex and age as co-variates (p < 0.01). To test the predictive capacity of GS at baseline to explain the variance in cognitive performance and social functioning at T2, a linear regression analysis was performed (p < 0.05).

RESULTS

Predictive relationships were found among GS when implicated with clinical, cognitive, and social variables. These relationships explained changes in cognitive performance after one year of follow-up; the variability percentage was 67.7%, in patients with type-2 diabetes mellitus and 89.1% in patients with schizophrenia. Baseline GS along with other variables, also predicted changes in social functioning in major depressive disorder, bipolar disorder, and schizophrenia, with variability percentages of 67.3, 36, and 59%, respectively.

CONCLUSION

GS combined with other variables significantly predicted changes in cognitive performance and social functioning in people with SMIs or type-2 diabetes mellitus. Interventions aimed to improve the overall physical conditions of patients who have poor GS could be a therapeutic option that confers positive effects on cognitive performance and social functioning.

Clinician-judged hearing impairment and associations with neuropathologic burden

OBJECTIVE

To examine whether neuropathologic burden is associated with hearing impairment.

METHODS

We studied 2,755 autopsied participants ≥55 years of age from the National Alzheimer's Coordinating Center database. Participants had at least 1 clinical evaluation at US National Institute on Aging-funded Alzheimer's Disease Center no more than 2 years before death. Patients were classified as hearing impaired by clinician report at baseline. Common dementia neuropathologies included Alzheimer disease pathologic change (Consortium to Establish a Registry for Alzheimer's Disease neuritic plaque density, neurofibrillary degeneration Braak stage), Lewy body disease, gross infarcts, and microinfarcts. Logistic regression models predicted impaired hearing with adjustment for age at death, sex, race, education, center, and follow-up time. Relative risks were calculated with the use of marginal standardization.

RESULTS

Impaired hearing was common (32%). In participants who were cognitively normal at baseline (n = 580), impaired hearing was associated with higher Braak stage (relative risk [RR] 1.33 per 2-stage increase, 95% confidence interval [CI] 1.06-1.66) but not other pathologies. In participants with dementia (n = 2,175), impaired hearing was positively associated with microinfarcts (RR 1.18, 95% CI 1.00-1.39) and inversely associated with neuritic plaque density (RR 0.91 per score increase, 95% CI 0.85-0.99). Development of impaired hearing in those with cognitive impairment was associated with neocortical Lewy bodies (1.26, 95% CI 1.02-1.55).

CONCLUSIONS

Impaired hearing, reported before the onset of cognitive impairment, was associated with increased neurofibrillary tangle burden. Impaired hearing in those with cognitive impairment was associated with microinfarcts and neocortical Lewy bodies but not typical Alzheimer disease pathologic change. Functional hearing problems may be a preclinical marker of neurofibrillary neurodegeneration, although replication is needed.

Healthy aging in elderly cochlear implant recipients: a multinational observational study

Background

Given an increase in the aging population and its impact on healthcare systems, policy makers for provision of health and social services are aiming to keep older adults in good health for longer, in other words towards ‘healthy aging’. Our study objective is to show that rehabilitation with cochlear implant treatment in the elderly with hearing impairment improves the overall health-related quality of life and general well-being that translate into healthy aging.

Methods

The multicentre, prospective, repeated measures, single-subject, clinical observational study will accrue 100 elderly, first-time, unilateral CI recipients (≥ 60 years) and analyze changes on specific measurement tools over ca. 20 months from preimplant to postimplant. Evaluations will consist of details collected through case history and interview questionnaires by clinicians, data logging, self-report questionnaires completed by the recipients and a series of commonly used audiometric measures and geriatric assessment tools. The primary indicator of changes in overall quality of life will be the HUI-3.

Discussion

The protocol is designed to make use of measurement tools that have already been applied to the hearing-impaired population in order to compare effects of CI rehabilitation in adults immediately before their implantation, (pre-implant) and after gaining 1–1.5 years of experience (post-implant). The broad approach will lead to a greater understanding of how useful hearing impacts the quality of life in elderly individuals, and thus improves potentials for healthy aging. Outcomes will be described and analyzed in detail.

Trial registration

This research has been registered in ClinicalTrials.gov (http://www.clinicaltrials.gov/), 7 March 2017 under the n° NCT03072862.

Hearing loss and cognitive function among Chinese older adults: the role of participation in leisure activities

BACKGROUND

Hearing loss, a highly prevalent sensory impairment affecting older adults, is a risk factor for cognition decline. However, there were very limited studies on this association in low-resource countries. This study aimed to assess the association between self-reported hearing loss and cognitive decline, and whether engagement in leisure activities moderated this association among older adults in China.

METHODS

Data were obtained from two waves of the nationally representative survey of China Longitudinal Healthy Longevity Survey (CLHLS) between 2011/12-2014. Eight thousand eight hundred forty-four individuals aged 65 years old or above with a dichotomized measure of self-reported hearing status were included. Modified Mini-Mental Examination (MMSE) was used to measure global cognition. Fixed-effects models were used to estimate whether leisure activity engagement moderated the association of self-perceived hearing loss with global cognitive change in the overall sample and sex subsamples.

RESULTS

Self-reported hearing loss was associated with cognitive impairment, with an odds ratio of 2.48 [1.22, 5.06]. Sex difference in the association of hearing loss and cognitive impairment was not found. Self-reported hearing loss was associated with cognitive decline, with 8% increase in risk compared with those with normal hearing. Frequent engagement in leisure activities moderated the association between hearing loss and cognitive decline for the whole and male samples.

CONCLUSION

Hearing loss was associated with cognitive decline, and leisure activities engagement moderated the association among males rather than females.

Auditory Processing Deficits Are Selectively Associated with Medial Temporal Lobe Mnemonic Function and White Matter Integrity in Aging Macaques

Deficits in auditory function and cognition are hallmarks of normative aging. Recent evidence suggests that hearing-impaired individuals have greater risks of developing cognitive impairment and dementia compared to people with intact auditory function, although the neurobiological bases underlying these associations are poorly understood. Here, a colony of aging macaques completed a battery of behavioral tests designed to probe frontal and temporal lobe-dependent cognition. Auditory brainstem responses (ABRs) and visual evoked potentials were measured to assess auditory and visual system function. Structural and diffusion magnetic resonance imaging were then performed to evaluate the microstructural condition of multiple white matter tracts associated with cognition. Animals showing higher cognitive function had significantly better auditory processing capacities, and these associations were selectively observed with tasks that primarily depend on temporal lobe brain structures. Tractography analyses revealed that the fractional anisotropy (FA) of the fimbria-fornix and hippocampal commissure were associated with temporal lobe-dependent visual discrimination performance and auditory sensory function. Conversely, FA of frontal cortex-associated white matter was not associated with auditory processing. Visual sensory function was not associated with frontal or temporal lobe FA, nor with behavior. This study demonstrates significant and selective relationships between ABRs, white matter connectivity, and higher-order cognitive ability.

Association between hearing loss and hereditary ATTR amyloidosis

Background: Hereditary transthyretin (TTR) related amyloidosis (ATTRv) is a life-threatening condition, which can potentially affect all organs. The objective was to identify the hearing status of patients with cardiac ATTRv and describe their audiological pattern. Methods: Nineteen patients with confirmed diagnosis of ATTRv cardiac amyloidosis (CA) underwent otoscopy and audiological tests, including pure tone and speech audiometry. Results: 74% were male, with a mean age of 72 ± 1.8 years. The main mutations were Val122Ile (n = 7) and Val30Met (n = 6). Objective hearing loss was detected in 17 patients (89%), whereas only 37% complained of hearing loss. ATTRv patients presented a different audiometric profile compared to patients of the same age with presbycusis: a higher prevalence and worse hearing thresholds compared to age-related expectations (ISO). Hearing loss affected all frequencies with, unexpectedly, mixed or conductive hearing loss (35%). According to the type of mutation, there was an increased rate of sensorineural or mixed/conductive hearing loss. Conclusions: the present study indicates that hearing loss is more prevalent and worse in patients with ATTRv amyloidosis than in the general population, while mostly clinically under-estimated. It suggests that ATTRv deposits could infiltrate the various anatomical structures of the inner and mild ear.

Agreement on the use of sensory screening techniques by nurses for older adults with cognitive impairment in long-term care: a mixed-methods consensus approach

OBJECTIVE

Based on two scoping reviews and two environmental scans, this study aimed at reaching consensus on the most suitable sensory screening tools for use by nurses working in long-term care homes, for the purpose of developing and validating a toolkit.

SETTING

A mixed-methods consensus study was conducted through two rounds of virtual electronic suitability rankings, followed by one online discussion group to resolve remaining disagreements.

PARTICIPANTS

A 12-member convenience panel of specialists from three countries with expertise in sensory and cognitive ageing provided the ranking data, of whom four participated in the online discussion.

OUTCOME MEASURES

As part of a larger mixed-methods project, the consensus was used to rank 22 vision and 20 hearing screening tests for suitability, based on 10 categories from the Quebec User Evaluation of Satisfaction with Assistive Technology questionnaire. Panellists were asked to score each test by category, and their responses were converted to z-scores, pooled and ranked. Outliers in assessment distribution were then returned to the individual team members to adjust scoring towards consensus.

RESULTS

In order of ranking, the top 4 vision screening tests were hand motion, counting fingers, confrontation visual fields and the HOT-V chart, whereas the top 4 hearing screening tests were the Hearing Handicap Inventory for the Elderly, the Whisper Test, the Measure of Severity of Hearing Loss and the Hyperacusis Questionnaire, respectively.

CONCLUSIONS

The final selection of vision screening tests relied on observable visual behaviours, such as visibility of tasks within the central or peripheral visual field, whereas three of the four hearing tests relied on subjective report. Next, feasibility will be tested by nurses using these tools in a long-term care setting with persons with various levels of cognitive impairment.

Frailty, Cognitive Decline, Neurodegenerative Diseases and Nutrition Interventions

Currently the human population is aging faster. This leads to higher dependency rates and the transformation of health and social care to adapt to this aged population. Among the changes developed by this population is frailty. It is defined as a clinically detectable syndrome, related to the aging of multiple physiological systems, which prompts a situation of vulnerability. The etiology of frailty seems to be multifactorial and its pathophysiology is influenced by the interaction of numerous factors. Morley et al. propose four main mechanisms triggering the frailty: atherosclerosis, sarcopenia, cognitive deterioration and malnutrition, with their respective metabolic alterations. Malnutrition is associated with cognitive impairment or functional loss, but it is also known that an inadequate nutritional status predisposes to cognitive frailty. Additionally, nutritional factors that may influence vascular risk factors will potentially have an effect on dementia decline among patients with cognitive frailty. This review aims to describe the nutritional factors that have been researched so far which may lead to the development of frailty, and especially cognitive decline.

Sensorial frailty: age-related hearing loss and the risk of cognitive impairment and dementia in later life

The peripheral hearing alterations and central auditory processing disorder (CAPD) associated with age-related hearing loss (ARHL), may impact cognitive disorders in older age. In older age, ARHL is also a significant marker for frailty, another age-related multidimensional clinical condition with a nonspecific state of vulnerability, reduced multisystem physiological reserve, and decreased resistance to different stressors (i.e. sensorial impairments, psychosocial stress, diseases, injuries). The multidimensional nature of frailty required an approach based on different pathogeneses because this clinical condition may include sensorial, physical, social, nutritional, cognitive, and psychological phenotypes. In the present narrative review, the cumulative epidemiological evidence coming from several longitudinal population-based studies, suggested convincing links between peripheral ARHL and incident cognitive decline and dementia. Moreover, a few longitudinal case-control and population-based studies also suggested that age-related CAPD in ARHL, may be central in determining an increased risk of incident cognitive decline, dementia, and Alzheimer's disease (AD). Cumulative meta-analytic evidence confirmed cross-sectional and longitudinal association of both peripheral ARHL and age-related CAPD with different domains of cognitive functions, mild cognitive impairment, and dementia, while the association with dementia subtypes such as AD and vascular dementia remained unclear. However, ARHL may represent a modifiable condition and a possible target for secondary prevention of cognitive impairment in older age, social isolation, late-life depression, and frailty. Further research is required to determine whether broader hearing rehabilitative interventions including coordinated counseling and environmental accommodations could delay or halt cognitive and global decline in the oldest old with both ARHL and dementia.

Hearing impairment and the risk of neurodegenerative dementia: A longitudinal follow-up study using a national sample cohort

This study aimed to explore the risk of dementia in a middle- and older-aged population with severe or profound hearing impairments. Data were collected for the Korean National Health Insurance Service-National Sample Cohort from 2002 to 2013. Participants aged 40 or older were selected. The 4,432 severely hearing-impaired participants were matched 1:4 with 17,728 controls, and the 958 profoundly hearing-impaired participants were matched 1:4 with 3,832 controls who had not reported any hearing impairment. Age, sex, income, region of residence, hypertension, diabetes mellitus, and dyslipidemia histories were matched between hearing-impaired and control groups. The crude (simple) and adjusted (age, sex, income, region of residence, dementia, hypertension, diabetes mellitus, dyslipidemia, ischemic heart disease, cerebrovascular disease, and depression) hazard ratios (HRs) of hearing impairment on dementia were analyzed using Cox-proportional hazard models. The severe hearing impairment group showed an increased risk of dementia (adjusted HR = 1.17, 95% confidence interval [CI] = 1.04–1.31, P = 0.010). The profound hearing impairment group also showed an increased risk of dementia (adjusted HR = 1.51, 95% CI = 1.14–2.00, P = 0.004). Both severe and profound hearing impairments were associated with elevated the risk of dementia in middle- and older-aged individuals.

The role of social frailty in explaining the association between hearing problems and mild cognitive impairment in older adults

BACKGROUND

We examined the role of social frailty in the association between hearing problems and mild cognitive impairment (MCI), and investigated which cognitive impairment domains are most strongly involved.

METHODS

Participants were 4251 older adults (mean age 72.5 ± 5.2 years, 46.1% male) who met the study inclusion criteria. Hearing problems were measured using the Hearing Handicap Inventory for the Elderly. Social frailty was identified using responses to five questions. Participants were divided into four groups depending on the presence of social frailty and hearing problems: control, social frailty, hearing problem, and co-occurrence. We assessed memory, attention, executive function, and processing speed using the National Center for Geriatrics and Gerontology-Functional Assessment Tool. Participants were categorized into normal cognition, single- and multiple-domain MCI, depending on the number of impaired cognitive domains.

RESULTS

Participants with multiple-domain MCI exhibited the highest odds ratios (OR) of the co-occurrence group (OR: 3.89, 95% confidence intervals [CI]: 1.96-7.72), followed by the social frailty (OR: 2.65, 95% CI: 1.49-4.67), and hearing problem (OR: 1.90, 95% CI: 1.08-3.34) groups, compared with the control group. However, single-domain MCI was not significantly associated with any group. Cognitive domain analysis revealed that impaired executive function and processing speed were associated with the co-occurrence, hearing problem, and social frailty groups, respectively.

CONCLUSIONS

Social frailty and hearing problems were independently associated with multiple-domain MCI. Comorbid conditions were more strongly associated with multiple-domain MCI. Longitudinal studies are needed to elucidate the causal role of social frailty in the association between hearing impairment and MCI.

Aetiologies of acquired deafblindness in a national sample

The present study provides an overview of aetiologies and co-morbidities of acquired deafblindness in a Danish national sample of 514 individuals above 50 years of age identified with acquired deafblindness. Information was obtained from a survey and a register. The most frequent aetiology of vision loss was age-related macular degeneration (55.4%). The most frequent aetiology of hearing loss was presbycusis (53.7%). The most frequent aetiology of acquired deafblindness was the combination of age-related macular degeneration and presbycusis (41.5%). However, among the younger participants (50–59 years of age), Usher syndrome was the most common aetiology (62.5%). The aetiologies of acquired deafblindness are many and constituted by several different combinations of hearing and vision loss aetiologies. The most frequent aetiologies are age related.

Cholinergic Hypofunction in Presbycusis-Related Tinnitus With Cognitive Function Impairment: Emerging Hypotheses

Presbycusis (age-related hearing loss) is a potential risk factor for tinnitus and cognitive deterioration, which result in poor life quality. Presbycusis-related tinnitus with cognitive impairment is a common phenotype in the elderly population. In these individuals, the central auditory system shows similar pathophysiological alterations as those observed in Alzheimer's disease (AD), including cholinergic hypofunction, epileptiform-like network synchronization, chronic inflammation, and reduced GABAergic inhibition and neural plasticity. Observations from experimental rodent models indicate that recovery of cholinergic function can improve memory and other cognitive functions via acetylcholine-mediated GABAergic inhibition enhancement, nicotinic acetylcholine receptor (nAChR)-mediated anti-inflammation, glial activation inhibition and neurovascular protection. The loss of cholinergic innervation of various brain structures may provide a common link between tinnitus seen in presbycusis-related tinnitus and age-related cognitive impairment. We hypothesize a key component of the condition is the withdrawal of cholinergic input to a subtype of GABAergic inhibitory interneuron, neuropeptide Y (NPY) neurogliaform cells. Cholinergic denervation might not only cause the degeneration of NPY neurogliaform cells, but may also result in decreased AChR activation in GABAergic inhibitory interneurons. This, in turn, would lead to reduced GABA release and inhibitory regulation of neural networks. Reduced nAChR-mediated anti-inflammation due to the loss of nicotinic innervation might lead to the transformation of glial cells and release of inflammatory mediators, lowering the buffering of extracellular potassium and glutamate metabolism. Further research will provide evidence for the recovery of cholinergic function with the use of cholinergic input enhancement alone or in combination with other rehabilitative interventions to reestablish inhibitory regulation mechanisms of involved neural networks for presbycusis-related tinnitus with cognitive impairment.

Impact of Aging on the Auditory System and Related Cognitive Functions: A Narrative Review

Age-related hearing loss (ARHL), presbycusis, is a chronic health condition that affects approximately one-third of the world's population. The peripheral and central hearing alterations associated with age-related hearing loss have a profound impact on perception of verbal and non-verbal auditory stimuli. The high prevalence of hearing loss in the older adults corresponds to the increased frequency of dementia in this population. Therefore, researchers have focused their attention on age-related central effects that occur independent of the peripheral hearing loss as well as central effects of peripheral hearing loss and its association with cognitive decline and dementia. Here we review the current evidence for the age-related changes of the peripheral and central auditory system and the relationship between hearing loss and pathological cognitive decline and dementia. Furthermore, there is a paucity of evidence on the relationship between ARHL and established biomarkers of Alzheimer's disease, as the most common cause of dementia. Such studies are critical to be able to consider any causal relationship between dementia and ARHL. While this narrative review will examine the pathophysiological alterations in both the peripheral and central auditory system and its clinical implications, the question remains unanswered whether hearing loss causes cognitive impairment or vice versa.

The risk of cognitive impairment associated with hearing function in older adults: a pooled analysis of data from eleven studies

Impaired hearing and cognition are disabling conditions among older adults. Research has presented inconsistent conclusions regarding hearing impairment posing a risk for cognitive impairment. We aimed to assess this from published evidence via searching PubMed and Embase, from the inception of the databases indexed to December 2, 2016. For those high-quality studies retrieved, relative risk (RR) and 95% confidence intervals (CIs) were combined to estimate the risk of cognitive impairment. Eleven cohort studies were included in the present study. Pooled results found that elderly people with disabled peripheral and central hearing function had a higher risk of cognitive impairment (for moderate/severe peripheral hearing impairment: RR = 1.29, 95% CI: 1.04-1.59 during a follow-up ≤6 years. RR = 1.57, 95% CI: 1.13-2.20 during a follow-up >6 years; for severe central hearing impairment, RR = 3.21, 95% CI: 1.19-8.69) compared to those with normal hearing function. We also recorded a dose-response trend for cognitive impairment as hearing thresholds rose. No evident bias from potential confounding factors was found with one exception: the length for clinical follow-up. Although results are preliminary because qualifying studies were few, statistical findings were consistent with older people identified as having greater levels of hearing loss, having a corresponding higher risk of cognitive impairment.