Hearing loss and its link to cognitive impairment and dementia

Rational Design of Inner Ear Drug Delivery Systems

The number of people with hearing loss disorders is enormous, causing great physical and mental stress to patients, as well as a huge social burden. Among these patients, hearing loss caused by inner ear lesions accounts for a large proportion. Therefore, treatment of the inner ear is important. Inner ear drug delivery systems, which can reduce the side effects of systemic drug administration by delivering drugs directly to the inner ear, are important in sensorineural hearing loss. Here, the development of inner ear drug delivery systems is focused, including the complex physiological structure that they face, types of drugs delivered, routes of administration, and forms of drug delivery carrier platforms. Recent studies in this process are presented and it is concluded with a summary and outlook on the problems faced and possible solutions.

Current status of research on the modifiable risk factors of dementia in India: A scoping review

Dementia is a progressive condition influenced by multiple modifiable risk factors. While 14 of these risk factors have been identified, most of the evidence stems from High Income Countries leaving a crucial gap in how these factors operate within the diverse context of India. A comprehensive search was conducted across PubMed, Web of Science, and Science Direct (2014-2024) to explore the association of cognitive impairment and dementia with at least one of the risk factors. Inclusion criteria encompassed empirical studies in India on the Indian population aged 18 and above while theoretical and review papers along with postmortem and animal samples were excluded. While the initial extraction of studies across the database identified 463 studies, only 15 that met the criteria were analyzed. Low education, depression, hypertension, and socioeconomic factors were commonly examined whereas hearing loss, high Low-Density Lipoprotein cholesterol, and air pollution were significantly underrepresented. The cross-sectional design and data from large study databases such as the Longitudinal Aging Study of India (LASI) were largely used. Findings showed that some risk factors replicate global trends, but obesity differs in the Indian context. Research on the modifiable risk factors of dementia in India remains limited with contextual variations, socioeconomic disparities, and environmental reasons playing a crucial role. Future studies need to utilize longitudinal designs, develop cross-culturally relevant cognitive assessments, and include under-represented populations. Furthermore, multidisciplinary team collaborations and region-specific interventions hold scope for the prevention, early detection, and management of dementia.

Hearing loss and the risk of dementia: A longitudinal analysis of the Korean National Health Insurance Service Senior Cohort

BackgroundHearing loss is a potentially modifiable risk factor implicated in dementia, with recent research suggesting an association between age-related hearing degradation and dementia.ObjectiveThis study aims to elucidate the relationship between hearing decline and dementia risk.MethodsWe analyzed data from 511,953 subjects from the Korean National Health Insurance Service-Senior Cohort (2002-2008). After excluding those diagnosed with dementia in 2002, 511,935 subjects were included. Subjects with hearing loss between 2002 and 2008 were selected and matched with a control group without hearing impairment based on age and gender. Statistical analyses, including Pearson's chi-squared test and the Cox proportional hazards model, were conducted, controlling for confounding variables such as household income and residential area. Subgroup analysis was also performed for Alzheimer's disease and vascular dementia.ResultsSubjects with hearing loss had a 1.245 times higher risk of all-cause dementia compared to those without hearing loss (adjusted hazard ratio over 3 years, 95% CI = 1.201-1.290), adjusting for gender, age, residence, and income. The adjusted hazard ratios for Alzheimer's disease over 3, 5, 7, and 10 years from the index date were 1.259 (95% CI = 1.211-1.308), 1.258 (95% CI = 1.208-1.310), 1.269 (95% CI = 1.215-1.325), and 1.235 (95% CI = 1.170-1.304), respectively. No significant association was found for vascular dementia, except for 3 years.ConclusionsHearing loss consistently increased the risk of all-cause dementia and Alzheimer's disease across timespans, suggesting a complex link between hearing loss and neurodegenerative diseases. These findings highlight the importance of early intervention and cognitive monitoring for individuals with hearing loss.

Blood Neurofilament Light Chain and Phospho-Tau 181 in Subjects with Mild Cognitive Impairment Due to Age-Related Hearing Loss

Background: Mild cognitive impairment is increasingly recognized as a precursor to more severe neurodegenerative conditions, particularly in the context of aging. Recent studies have highlighted the intersection of hearing loss and cognitive decline, suggesting that auditory deficits may exacerbate cognitive impairments in older adults, proposing the use of hearing aids to mitigate cognitive decline, and indicating that early intervention in hearing loss could be crucial for preserving cognitive function. The underlying mechanisms of the relationship between hearing and cognitive impairment may involve neuroinflammatory processes and neurodegeneration. Recent studies have evidenced the role of tau proteins and neurofilaments as biomarkers in the onset and progression of neurodegenerative diseases. Methods: We selected 30 subjects with age-related hearing loss, and we evaluated their cognitive status through the administration of screening tests, which also measured neurofilament light chain and phospho-tau 181 serum levels as biomarkers of neurodegeneration. The subjects were re-evaluated six months after the hearing aid fitting. Results: Patients with hearing impairment presented slightly altered results on cognitive tests, typical of a mild cognitive impairment. At the same time, serum levels of neurofilament light chain and phospho-tau 181 were significantly increased compared to the matched control group. After the hearing aids fitting, auditory, cognitive, and serum values results improved. Conclusions: The results of the study highlight the cognitive involvement in patients with hearing impairment and identify neurofilament light chain and phospho-tau 181 as serum biomarkers of neurodegeneration useful in monitoring the pathology.

Hearing modulation affects Alzheimer's disease progression linked to brain inflammation: a study in mouse models

BACKGROUND

Recent studies have identified hearing loss (HL) as a primary risk factor for Alzheimer's disease (AD) onset. However, the mechanisms linking HL to AD are not fully understood. This study explored the effects of drug-induced hearing loss (DIHL) on the expression of proteins associated with AD progression in mouse models.

METHODS

DIHL was induced in 5xFAD and Tg2576 mice aged 3 to 3.5 weeks using kanamycin (700 mg/kg, subcutaneous) and furosemide (600 mg/kg, intraperitoneal). The accumulation and expression of beta-amyloid (Aβ), ionized calcium-binding adaptor molecule 1 (Iba1), and glial fibrillary acidic protein (GFAP) were measured through immunohistochemistry and immunoblotting. Additionally, the expression of proteins involved in the mammalian target of rapamycin (mTOR) pathway, including downstream effectors p70 ribosomal S6 kinase (p70S6K) and S6, as well as proinflammatory cytokines, was analyzed.

RESULTS

Compared to control conditions, HL led to a significant increase in the accumulation of Aβ in the hippocampus and cortex. Elevated levels of neuroinflammatory markers, including Iba1 and GFAP, as well as proinflammatory cytokines such as interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α), were observed. Moreover, DIHL enhanced phosphorylation of mTOR, p70S6K, and S6, indicating activation of the mTOR pathway.

CONCLUSIONS

HL significantly increases Aβ accumulation in the brain. Furthermore, HL activates astrocytes and microglia, leading to increased neuroinflammation and thereby accelerating AD progression. These findings strongly suggest that HL contributes autonomously to neuroinflammation, highlighting the potential for early intervention in HL to reduce AD risk.

Hearing and vision rehabilitation for people with dementia in five European countries (SENSE-Cog): a randomised controlled trial

BACKGROUND

The effect of hearing and vision difficulties on the risk of developing dementia and worsening outcomes in people already living with dementia is well established. We evaluated the clinical impact of a hearing and vision rehabilitation and support programme on quality of life in people with mild-to-moderate dementia and concurrent sensory difficulties.

METHODS

We conducted a parallel-group, multicentre, observer-blind, superiority randomised controlled trial in seven older adult clinics in five European countries (Cyprus, France, Greece, Ireland, and the UK). People with mild-to-moderate dementia with adult-acquired hearing difficulties, vision difficulties, or both were randomly assigned (1:1) along with their care partner to an 18-week home-basedsensory support intervention (SSI) of tailored hearing and vision rehabilitation and support, or to care as usual. Randomisation was blocked (block size of four, six, or eight) and stratified by country, with allocation assigned via a remote web-based system. The SSI included: full hearing assessment, vision assessment, or both; fitting of hearing aids, glasses, or other sensory aids; and home-based support from a sensory support therapist to assist adherence and uptake of sensory aids, foster social networking, and optimise the home sensory environment. Care as usual involved no additional intervention beyond services normally available to people with dementia at the respective sites. The primary outcome was health-related quality of life (Dementia Quality of Life Instrument [DEMQoL]) score at 36 weeks, reported as an adjusted mean difference. Analyses were done according to the intention-to-treat principle. This trial is registered with the ISRCTN Registry, ISRCTN17056211.

FINDINGS

Between May 4, 2018, and May 6, 2021, 252 people with mild-to-moderate dementia were randomly assigned, of whom 251 (n=126 in the SSI group and n=125 in the care as usual group) were included in the analysis. The mean age of participants was 79·6 years (SD 5·8), and 132 (53%) were women. After a median follow-up time of 37·7 weeks (IQR 36·2-39·0), the mean DEMQoL score was 92·8 (SD 15·2) in the SSI group and 92·8 (14·0) in the care as usual group (adjusted difference 0·18, 95% CI -2·13 to 2·30, p=0·87). Among 114 adverse events reported for 56 (44%) participants in the SSI group, ten events in nine participants were related or possibly related to the intervention (medical device pain or discomfort n=6, ear pain n=1, scratch to the ear n=1, sore eye n=1, redness n=1; all of grade 1). Serious adverse events were reported for 25 (20%) participants in the SSI group and 16 (13%) in the care as usual group. Six (5%) participants in the SSI group and five (4%) in the care as usual group died. None of the serious adverse events or deaths were related to the study intervention or procedures.

INTERPRETATION

This study showed no improvement in quality in life in participants who received the intervention in the longer term. Sensory difficulties are common in people with dementia and interventions aimed at improving sensory-cognitive health should be explored further.

FUNDING

EU Horizon 2020.

Sound and Alzheimer's Disease-From Harmful Noise to Beneficial Soundscape Augmentation and Music Therapy

Exposure to sound energy may be a risk factor or a therapeutic intervention for Alzheimer's disease (AD). On one hand, noise has a harmful effect on people with AD by contributing to hearing loss, sleep disturbance, oxidative stress, inflammation, and excitotoxicity. But on the other hand, clinical trials and nursing home interventions with soundscape augmentation involving natural sounds have shown promising results in alleviating psychophysiological symptoms in people with AD. Music therapy, an emerging non-pharmacological treatment, can improve cognition, reduce anxiety and depression, and enhance self-awareness in patients with AD. To ensure that music does not become noise in clinical trials, only favorite music at levels safe for hearing should be used. From a public health standpoint, noise countermeasures, soundscape augmentation with natural sounds, and active or passive engagement with music may be regarded as potentially powerful strategies for the prevention of AD.

Age-Related Hearing Loss, Cognitive Decline, and Social Interaction: Testing a Framework

PURPOSE

Aging increases risk for hearing loss, cognitive decline, and social isolation; however, the nature of their interconnection remains unclear. This study examined the interplay between age-related hearing loss, cognitive decline, and social isolation in adults by testing the ability to understand speech in background noise, a challenge frequently reported by many older adults.

METHOD

We analyzed data collected from 128 adults (20-79 years of age, Mage = 51 years) recruited as part of the Aging Brain Cohort at the University of South Carolina repository. The participants underwent testing for hearing, cognition, and social interaction, which included pure-tone audiometry, a words-in-noise (WIN) test, a hearing questionnaire (Speech, Spatial and Qualities of Hearing Scale [SSQ12]), a social questionnaire (Patient-Reported Outcomes Measurement Information System-57 Social), and the Montreal Cognitive Assessment. We used a single pure-tone average (PTA) threshold value and a single WIN threshold value for each participant because there were no differences on average between the left and right ears.

RESULTS

Poorer hearing was significantly associated with cognitive decline, through both PTA and WIN thresholds, with a stronger association observed for WIN threshold. Adults with poorer hearing also exhibited greater social isolation, as evidenced by their WIN threshold and SSQ12 score, although not through PTA. This connection was more pronounced with the WIN threshold than with the SSQ12 score. Cognition was not related to social isolation, suggesting that social isolation is affected more by the ability to understand words in noise than by cognition in a nondemented population.

CONCLUSIONS

Understanding speech in challenging auditory environments rather than mere threshold detection is strongly linked to social isolation and cognitive decline. Thus, inclusion of a word-recognition-in-noise test and a social isolation survey in clinical settings is warranted.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.26237060.

Parallel Multilink Group Joint ICA: Fusion of 3D Structural and 4D Functional Data Across Multiple Resting fMRI Networks

Multimodal neuroimaging research plays a pivotal role in understanding the complexities of the human brain and its disorders. Independent component analysis (ICA) has emerged as a widely used and powerful tool for disentangling mixed independent sources, particularly in the analysis of functional magnetic resonance imaging (fMRI) data. This paper extends the use of ICA as a unifying framework for multimodal fusion, introducing a novel approach termed parallel multilink group joint ICA (pmg-jICA). The method allows for the fusion of gray matter maps from structural MRI (sMRI) data to multiple fMRI intrinsic networks, addressing the limitations of previous models. The effectiveness of pmg-jICA is demonstrated through its application to an Alzheimer's dataset, yielding linked structure-function outputs for 53 brain networks. Our approach leverages the complementary information from various imaging modalities, providing a unique perspective on brain alterations in Alzheimer's disease. The pmg-jICA identifies several components with significant differences between HC and AD groups including thalamus, caudate, putamen with in the subcortical (SC) domain, insula, parahippocampal gyrus within the cognitive control (CC) domain, and the lingual gyrus within the visual (VS) domain, providing localized insights into the links between AD and specific brain regions. In addition, because we link across multiple brain networks, we can also compute functional network connectivity (FNC) from spatial maps and subject loadings, providing a detailed exploration of the relationships between different brain regions and allowing us to visualize spatial patterns and loading parameters in sMRI along with intrinsic networks and FNC from the fMRI data. In essence, developed approach combines concepts from joint ICA and group ICA to provide a rich set of output characterizing data-driven links between covarying gray matter networks, and a (potentially large number of) resting fMRI networks allowing further study in the context of structure/function links. We demonstrate the utility of the approach by highlighting key structure/function disruptions in Alzheimer's individuals.

A Consolidated Understanding of the Contribution of Redox Dysregulation in the Development of Hearing Impairment

The etiology of hearing impairment is multifactorial, with contributions from both genetic and environmental factors. Although genetic studies have yielded valuable insights into the development and function of the auditory system, the contribution of gene products and their interaction with alternate environmental factors for the maintenance and development of auditory function requires further elaboration. In this review, we provide an overview of the current knowledge on the role of redox dysregulation as the converging factor between genetic and environmental factor-dependent development of hearing loss, with a focus on understanding the interaction of oxidative stress with the physical components of the peripheral auditory system in auditory disfunction. The potential involvement of molecular factors linked to auditory function in driving redox imbalance is an important promoter of the development of hearing loss over time.