Deficit in Central Auditory Processing as a Biomarker of Pre-Clinical Alzheimer's Disease

Hearing Loss and Cognitive Decline in the Aging Population: Emerging Perspectives in Audiology

In this perspective article, the author explores the connections between hearing loss, central auditory processing, and cognitive decline, offering insights into the complex dynamics at play. Drawing upon a range of studies, the relationship between age-related central auditory processing disorders and Alzheimer's disease is discussed, with the aim of enhancing our understanding of these interconnected conditions. Highlighting the evolving significance of audiologists in the dual management of cognitive health and hearing impairments, the author focuses on their role in identifying early signs of cognitive impairment and evaluates various cognitive screening tools used in this context. The discussion extends to adaptations of hearing assessments for older adults, especially those diagnosed with dementia, and highlights the significance of objective auditory electrophysiological tests. These tests are presented as vital in assessing the influence of aging and Alzheimer's disease on auditory processing capabilities and to signal cognitive dysfunction. The article underscores the critical role of audiologists in addressing the challenges faced by the aging population. The perspective calls for further research to improve diagnostic and therapeutic strategies in audiology, and emphasizes the need for a multidisciplinary approach in tackling the nexus of hearing loss, auditory processing, and cognitive decline.

Subjective hearing loss is not associated with an increased risk of Alzheimer's disease dementia

Hearing loss is a risk-factor for dementia but the reasons for this are unclear. Subjective hearing loss is related to increased future dementia risk, however, this metric has not been previously examined with cognitive, neuroimaging and biochemical measures that are relevant to Alzheimer's disease. We assessed Cognitively Normal and Mild Cognitively Impaired participants from the Alzheimer's Disease Neuroimaging Initiative with subjective hearing loss to examine if they had faster decline in episodic memory scores, hippocampal volume and greater pTau positivity. The likelihood of a dementia diagnosis in hearing impaired participants over a 5-year period was also assessed. There were no statistically significant differences between the hearing subgroups over a 5-year period nor were there in conversions to a dementia diagnosis. Objective hearing loss metrics may provide a more reliable link between hearing loss and dementia risk.

Constructing hierarchical attentive functional brain networks for early AD diagnosis

Analyzing functional brain networks (FBN) with deep learning has demonstrated great potential for brain disorder diagnosis. The conventional construction of FBN is typically conducted at a single scale with a predefined brain region atlas. However, numerous studies have identified that the structure and function of the brain are hierarchically organized in nature. This urges the need of representing FBN in a hierarchical manner for more effective analysis of the complementary diagnostic insights at different scales. To this end, this paper proposes to build hierarchical FBNs adaptively within the Transformer framework. Specifically, a sparse attention-based node-merging module is designed to work alongside the conventional network feature extraction modules in each layer. The proposed module generates coarser nodes for further FBN construction and analysis by combining fine-grained nodes. By stacking multiple such layers, a hierarchical representation of FBN can be adaptively learned in an end-to-end manner. The hierarchical structure can not only integrate the complementary information from multiscale FBN for joint analysis, but also reduce the model complexity due to decreasing node sizes. Moreover, this paper argues that the nodes defined by the existing atlases are not necessarily the optimal starting level to build FBN hierarchy and exploring finer nodes may further enrich the FBN representation. In this regard, each predefined node in an atlas is split into multiple sub-nodes, overcoming the scale limitation of the existing atlases. Extensive experiments conducted on various data sets consistently demonstrate the superior performance of the proposed method over the competing methods.

Sensory Loss and Risk of Dementia

Sensory loss in olfaction, vision, and hearing is a risk factor for dementia, but the reasons for this are unclear. This review presents the neurobiological evidence linking each sensory modality to specific dementias and explores the potential mechanisms underlying this. Olfactory deficits can be linked to direct neuropathologic changes in the olfactory system due to Alzheimer disease and Parkinson disease, and may be a marker of disease severity. Visual deficits potentially increase dementia risk in a vulnerable individual by reducing resilience to dementia. Hearing deficits may indicate a susceptibility to Alzheimer disease through a variety of mechanisms. More generally, sensory impairment could be related to factors associated with resilience against dementia. Further research is needed to tease out the specific and synergistic effects of sensory impairment. Studying sensory loss in relation to neurodegenerative biomarkers is necessary to clarify the mechanisms involved. This could produce new monitoring and management strategies for people at risk of dementia.

Predicting Brain Amyloid Status Using the National Institute of Health Toolbox (NIHTB) for Assessment of Neurological and Behavioral Function

BACKGROUND

Amyloid-beta (Aβ) plaque is a neuropathological hallmark of Alzheimer's disease (AD). As anti-amyloid monoclonal antibodies enter the market, predicting brain amyloid status is critical to determine treatment eligibility.

OBJECTIVE

To predict brain amyloid status utilizing machine learning approaches in the Advancing Reliable Measurement in Alzheimer's Disease and Cognitive Aging (ARMADA) study.

DESIGN

ARMADA is a multisite study that implemented the National Institute of Health Toolbox for Assessment of Neurological and Behavioral Function (NIHTB) in older adults with different cognitive ability levels (normal, mild cognitive impairment, early-stage dementia of the AD type).

SETTING

Participants across various sites were involved in the ARMADA study for validating the NIHTB.

PARTICIPANTS

199 ARMADA participants had either PET or CSF information (mean age 76.3 ± 7.7, 51.3% women, 42.3% some or complete college education, 50.3% graduate education, 88.9% White, 33.2% with positive AD biomarkers).

MEASUREMENTS

We used cognition, emotion, motor, sensation scores from NIHTB, and demographics to predict amyloid status measured by PET or CSF. We applied LASSO and random forest models and used the area under the receiver operating curve (AUROC) to evaluate the ability to identify amyloid positivity.

RESULTS

The random forest model reached AUROC of 0.74 with higher specificity than sensitivity (AUROC 95% CI:0.73 - 0.76, Sensitivity 0.50, Specificity 0.88) on the held-out test set; higher than the LASSO model (0.68 (95% CI:0.68 - 0.69)). The 10 features with the highest importance from the random forest model are: picture sequence memory, cognition total composite, cognition fluid composite, list sorting working memory, words-in-noise test (hearing), pattern comparison processing speed, odor identification, 2-minutes-walk endurance, 4-meter walk gait speed, and picture vocabulary. Overall, our model revealed the validity of measurements in cognition, motor, and sensation domains, in associating with AD biomarkers.

CONCLUSION

Our results support the utilization of the NIH toolbox as an efficient and standardizable AD biomarker measurement that is better at identifying amyloid negative (i.e., high specificity) than positive cases (i.e., low sensitivity).

Identification of appropriate tools to gauge brain functions in a clinical setup of a developing country: A pilot study

Objective

To identify the most appropriate tools to measure functions of the brain that can be utilized in the clinical setups of developing countries.

Methods

This qualitative research with a three-step approach was carried out from January 2022 to May 2022 at the Institute of Basic Medical Sciences, Khyber Medical University, Pakistan. Firstly, literature was searched to identify main brain faculties, then interviews were conducted with regional field experts to identify appropriate scales for the selected functions. Lastly a rubric was filled using interview transcripts and literature.

Results

The identified functions were vision, hearing, cognition, motor and emotions. Based on the rubric the best tests were visual fields (17/24), pure tone audiometry (16/24), Mini-Mental State Exam (20/24), Trait Emotional Intelligence Questionnaire (18/24), Romberg's test (19/24) and Manual Muscle Testing (18/24).

Conclusion

The clinicians in developing countries can utilize the visual fields, pure tone audiometry, Mini-Mental State Exam, Trait Emotional Intelligence Questionnaire, Romberg's test and Manual Muscle Testing for most efficient, feasible, accurate and cost-effective measurement of brain functions.

Promoting hearing and cognitive health in audiologic rehabilitation for the well-being of older adults

OBJECTIVE

With our aging population, an increasing number of older adults with hearing loss have cognitive decline. Hearing care practitioners have an important role in supporting healthy aging and should be knowledgeable about cognitive decline and associated management strategies to maximize successful hearing intervention.

METHODS

A review of current research and expert opinion.

RESULTS

This article outlines the association between hearing loss and cognitive decline/dementia, hypothesized mechanisms underlying this, and considers current research into the effects of hearing intervention on cognitive decline. Cognition into old age, cognitive impairment, dementia, and how to recognize cognitive decline that is not part of normal aging are described. Screening of older asymptomatic adults for cognitive decline and practical suggestions for the delivery of person-centered hearing care are discussed. Holistic management goals, personhood, and person-centered care in hearing care management are considered for older adults with normal cognitive aging through to dementia. A case study illustrates important skills and potential management methods. Prevention strategies for managing hearing and cognitive health and function through to older age, and strategies to maximize successful hearing aid use are provided.

CONCLUSION

This article provides evidence-based recommendations for hearing care professionals supporting older clients to maximize well-being through the cognitive trajectory.

Association of Central Auditory Processing Dysfunction With Preclinical Alzheimer's Disease

OBJECTIVE

To investigate whether central auditory processing dysfunction measured by the dichotic digit test-1 digit (DDT1) is present in preclinical Alzheimer's disease (AD) individuals who are cognitively normal (CN) older adults with the cerebral beta-amyloid (Aβ) deposition and to explore the potential of the DDT1 as a screening test for preclinical AD.

STUDY DESIGN

Cross-sectional design.

SETTING

A prospective observational cohort study.

METHODS

CN older adults with a global clinical dementia rating score of 0 were included. The hearing test battery including pure-tone audiometry, speech audiometry, distortion product otoacoustic emission, and DDT1 was administered to participants.

RESULTS

Fifty CN older adults were included. Among them, 38 individuals were included in the Aβ deposition negative (AN) group and 12 were included in the Aβ deposition positive (AP) group. The DDT1 scores of both the better and worse ears were significantly lower in the AP group than in the AN group (p = .008 and p = .015, respectively). No significant differences were observed between the groups in tests of the peripheral auditory pathways. In multivariable logistic regression analysis adjusted for apolipoprotein E4 positivity, the DDT1 better ear score predicted the AP group (p = .036, odds ratio = 0.892, 95% confidence interval: 0.780-0.985) with relatively high diagnostic accuracy.

CONCLUSION

Our findings suggest that Aβ deposition may affect the central auditory pathway even before cognitive decline appears. DDT1, which can easily be applied to the old-age population, may have the potential as a screening tool for preclinical AD.

Visual Evoked Potentials as an Early-Stage Biomarker in the rTg4510 Tauopathy Mouse Model

Background: Tauopathies such as Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are characterized by formation of neurofibrillary tangles consisting of hyperphosphorylated tau protein. Early pathophysiological and functional changes related to neurofibrillary tangles formation are considered to occur prior to extensive neurodegeneration. Hyperphosphorylated tau has been detected in postmortem retinas of AD and FTD patients, and the visual pathway is an easily accessible system in a clinical setting. Hence, assessment of the visual function may offer the potential to detect consequences of early tau pathology in patients. Objective: The aim of this study was to evaluate visual function in a tauopathy mouse model in relation to tau hyperphosphorylation and neurodegeneration. Methods: In this study we explored the association between the visual system and functional consequences of tau pathology progression using a tauopathy rTg4510 mouse model. To this end, we recorded full-field electroretinography and visual evoked potentials in anesthetized and awake states at different ages. Results: While retinal function remained mostly intact within all the age groups investigated, we detected significant changes in amplitudes of visual evoked potential responses in young rTg4510 mice exhibiting early tau pathology prior to neurodegeneration. These functional alterations in the visual cortex were positively correlated with pathological tau levels. Conclusion: Our findings suggest that visual processing could be useful as a novel electrophysiological biomarker for early stages of tauopathy.

Cortical thickness of the left parahippocampal cortex links central hearing and cognitive performance in aging

Hearing impairment is considered a leading modifiable risk factor of cognitive decline and dementia. While most evidence has been established on clinical assessment of peripheral hearing loss, understanding of how central hearing in real-world conditions is associated with cognitive aging is limited. This study analyzed the data of 473 unrelated healthy adults aged 36-100 years old from the Lifespan Human Connectome Project in Aging. Central hearing was evaluated using the Words-in-Noise decibel threshold. Cognitive functions were evaluated by the performance on cognitive tests, and cortical thickness was estimated from magnetic resonance imaging (MRI) data. Here, we show that a higher hearing threshold was associated with a lower performance on immediate and delayed episodic memory retrieval, switching aspect of executive function, working memory, reading decoding, and vocabulary comprehension. Cortical thickness in the left parahippocampal cortex (lPHC) was negatively associated with the hearing threshold and acted as a significant partial mediator in the association of central hearing with immediate recall, switching, reading decoding, and vocabulary comprehension. These findings suggest that cortical thickness in the lPHC, an early target of dementia, partially links central hearing and performance in multiple cognitive domains in aging.

Hearing impairment is associated with cognitive decline, brain atrophy and tau pathology

BACKGROUND

Hearing impairment was recently identified as the most prominent risk factor for dementia. However, the mechanisms underlying the link between hearing impairment and dementia are still unclear.

METHODS

We investigated the association of hearing performance with cognitive function, brain structure and cerebrospinal fluid (CSF) proteins in cross-sectional, longitudinal, mediation and genetic association analyses across the UK Biobank (N = 165,550), the Chinese Alzheimer's Biomarker and Lifestyle (CABLE, N = 863) study, and the Alzheimer's Disease Neuroimaging Initiative (ADNI, N = 1770) database.

FINDINGS

Poor hearing performance was associated with worse cognitive function in the UK Biobank and in the CABLE study. Hearing impairment was significantly related to lower volume of temporal cortex, hippocampus, inferior parietal lobe, precuneus, etc., and to lower integrity of white matter (WM) tracts. Furthermore, a higher polygenic risk score (PRS) for hearing impairment was strongly associated with lower cognitive function, lower volume of gray matter, and lower integrity of WM tracts. Moreover, hearing impairment was correlated with a high level of CSF tau protein in the CABLE study and in the ADNI database. Finally, mediation analyses showed that brain atrophy and tau pathology partly mediated the association between hearing impairment and cognitive decline.

INTERPRETATION

Hearing impairment is associated with cognitive decline, brain atrophy and tau pathology, and hearing impairment may reflect the risk for cognitive decline and dementia as it is related to bran atrophy and tau accumulation in brain. However, it is necessary to assess the mechanism in future animal studies.

FUNDING

A full list of funding bodies that supported this study can be found in the Acknowledgements section.

The hearing hippocampus

The hippocampus has a well-established role in spatial and episodic memory but a broader function has been proposed including aspects of perception and relational processing. Neural bases of sound analysis have been described in the pathway to auditory cortex, but wider networks supporting auditory cognition are still being established. We review what is known about the role of the hippocampus in processing auditory information, and how the hippocampus itself is shaped by sound. In examining imaging, recording, and lesion studies in species from rodents to humans, we uncover a hierarchy of hippocampal responses to sound including during passive exposure, active listening, and the learning of associations between sounds and other stimuli. We describe how the hippocampus' connectivity and computational architecture allow it to track and manipulate auditory information - whether in the form of speech, music, or environmental, emotional, or phantom sounds. Functional and structural correlates of auditory experience are also identified. The extent of auditory-hippocampal interactions is consistent with the view that the hippocampus makes broad contributions to perception and cognition, beyond spatial and episodic memory. More deeply understanding these interactions may unlock applications including entraining hippocampal rhythms to support cognition, and intervening in links between hearing loss and dementia.

Amyloid Pathology in the Central Auditory Pathway of 5XFAD Mice Appears First in Auditory Cortex

Background: Effective treatment of Alzheimer’s disease (AD) will hinge on early detection. This has led to the search for early biomarkers that use non-invasive testing. One possible early biomarker is auditory temporal processing deficits, which reflect central auditory pathway dysfunction and precede cognitive and memory declines in AD. Gap detection is a measure of auditory temporal processing, is impaired in human AD, and is also impaired in the 5XFAD mouse model of AD. Gap detection deficits appear as early as postnatal day 60 in 5XFAD mice, months before cognitive deficits or cell death, supporting gap detection as an early biomarker. However, it remains unclear how gap detection deficits relate to the progression of amyloid pathology in the auditory system. Objective: To determine the progression of amyloid pathology throughout the central auditory system and across age in 5XFAD mice. Methods: We quantified intracellular and extracellular antibody labelling of Aβ 42 in 6 regions of the central auditory system from p14 to p150. Results: Pathology appeared first in primary auditory cortex (A1) as intracellular accumulation of Aβ 42 in layer 5 pyramidal neurons by age p21. Extracellular plaques appeared later, by age p90, in A1, medial geniculate body, and inferior colliculus. Auditory brainstem structures showed minimal amyloid pathology. We also observed pathology in the caudal pontine reticular nucleus, a brainstem structure that is outside of the central auditory pathway but which is involved in the acoustic startle reflex. Conclusion: These results suggest that Aβ 42 accumulation, but not plaques, may impair gap detection.

Clinical Features and Potential Mechanisms Relating Neuropathological Biomarkers and Blood-Brain Barrier in Patients With Alzheimer’s Disease and Hearing Loss

Background

The aim of this study was to explore clinical features and potential mechanisms relating neuropathological biomarkers and blood-brain barrier (BBB) in Alzheimer’s disease (AD) and hearing loss (HL).

Materials and Methods

A total of 65 patients with AD were recruited and auditory function was assessed by threshold of pure tone audiometry (PTA). Patients were divided into AD with HL (AD-HL) and AD with no HL (AD-nHL) groups based on the standard of World Health Organization. Clinical symptoms were assessed by multiple rating scales. The levels of neuropathological biomarkers of β amyloid1-42 (Aβ_1–42) and multiple phosphorylated tau (P-tau), and BBB factors of matrix metalloproteinases (MMPs), receptor of advanced glycation end products, glial fibrillary acidic protein, and low-density lipoprotein receptor related protein 1 were measured.

Results

(1) Compared with AD-nHL group, AD-HL group had significantly impaired overall cognitive function and cognitive domains of memory, language, attention, execution, and activities of daily living (ADL) reflected by the scores of rating scales (P < 0.05). PTA threshold was significantly correlated with the impairments of overall cognitive function and cognitive domains of memory and language, and ADL in patients with AD (P < 0.05). (2) P-tau (S199) level was significantly increased in CSF from AD-HL group (P < 0.05), and was significantly and positively correlated with PTA threshold in patients with AD. (3) MMP-3 level was significantly elevated in CSF from AD-HL group (P < 0.05), and was significantly and positively correlated with PTA threshold in patients with AD (P < 0.05). (4) In AD-HL group, P-tau (S199) level was significantly and positively correlated with the levels of MMP-2 and MMP-3 in CSF (P < 0.05).

Conclusion

AD-HL patients have severely compromised overall cognitive function, multiple cognitive domains, and ADL. The potential mechanisms of AD-HL involve elevations of AD neuropathological biomarker of P-tau (S199) and BBB factor of MMP-3, and close correlations between P-tau (S199) and MMP-2/MMP-3 in CSF. Findings from this investigation highly suggest significance of early evaluation of HL for delaying AD progression, and indicate new directions of drug development by inhibiting neuropathological biomarkers of AD and protecting BBB.

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.

Central Auditory Functions of Alzheimer's Disease and Its Preclinical Stages: A Systematic Review and Meta-Analysis

In 2020, 55 million people worldwide were living with dementia, and this number is projected to reach 139 million in 2050. However, approximately 75% of people living with dementia have not received a formal diagnosis. Hence, they do not have access to treatment and care. Without effective treatment in the foreseeable future, it is essential to focus on modifiable risk factors and early intervention. Central auditory processing is impaired in people diagnosed with Alzheimer's disease (AD) and its preclinical stages and may manifest many years before clinical diagnosis. This study systematically reviewed central auditory processing function in AD and its preclinical stages using behavioural central auditory processing tests. Eleven studies met the full inclusion criteria, and seven were included in the meta-analyses. The results revealed that those with mild cognitive impairment perform significantly worse than healthy controls within channel adaptive tests of temporal response (ATTR), time-compressed speech test (TCS), Dichotic Digits Test (DDT), Dichotic Sentence Identification (DSI), Speech in Noise (SPIN), and Synthetic Sentence Identification-Ipsilateral Competing Message (SSI-ICM) central auditory processing tests. In addition, this analysis indicates that participants with AD performed significantly worse than healthy controls in DDT, DSI, and SSI-ICM tasks. Clinical implications are discussed in detail.

APOE, TOMM40, and sex interactions on neural network connectivity

The Apolipoprotein E ε4 (APOE ε4) haplotype is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). The Translocase of Outer Mitochondrial Membrane-40 (TOMM40) gene maintains cellular bioenergetics, which is disrupted in AD. TOMM40 rs2075650 ('650) G versus A carriage is consistently related to neural and cognitive outcomes, but it is unclear if and how it interacts with APOE. We examined 21 orthogonal neural networks among 8,222 middle-aged to aged participants in the UK Biobank cohort. ANOVA and multiple linear regression tested main effects and interactions with APOE and TOMM40 '650 genotypes, and if age and sex acted as moderators. APOE ε4 was associated with less strength in multiple networks, while '650 G versus A carriage was related to more language comprehension network strength. In APOE ε4 carriers, '650 G-carriage led to less network strength with increasing age, while in non-G-carriers this was only seen in women but not men. TOMM40 may shift what happens to network activity in aging APOE ε4 carriers depending on sex.

Association of Performance on Dichotic Auditory Tests With Risk for Incident Dementia and Alzheimer Dementia

Importance

Age-related hearing difficulties can include problems with signal audibility and central auditory processing. Studies have demonstrated associations between audibility and dementia risk. To our knowledge, limited data exist to determine whether audibility, central processing, or both drive these associations.

Objective

To determine the associations between signal sensitivity, central auditory processing, and dementia and Alzheimer dementia (AD) risk.

Design, Setting, and Participants

This follow-up observational study of a sample from the prospective Adult Changes in Thought study of dementia risk was conducted at Kaiser Permanente Washington, a western Washington health care delivery system, and included 280 volunteer participants without dementia who were evaluated from October 2003 to February 2006 with follow-up through September 2018. Analyses began in 2019 and continued through 2021.

Exposures

Hearing tests included pure tone signal audibility, a monaural word recognition test, and 2 dichotic tests: the Dichotic Sentence Identification (DSI) test and the Dichotic Digits test (DDT).

Main Outcomes and Measures

Cognition was assessed biennially with the Cognitive Abilities Screening Instrument (range, 1-100; higher scores are better), and scores of less than 86 prompted clinical and neuropsychological evaluations. All data were reviewed at multidisciplinary consensus conferences, and standardized criteria were used to define incident cases of dementia and probable or possible AD. Cox proportional hazard models were used to determine associations with hearing test performance.

Results

A total of 280 participants (177 women [63%]; mean [SD] age, 79.5 [5.2] years). As of September 2018, there were 2196 person-years of follow-up (mean, 7.8 years) and 89 incident cases of dementia (66 not previously analyzed), of which 84 (94.4%) were AD (63 not previously analyzed). Compared with people with DSI scores of more than 80, the dementia adjusted hazard ratio (aHR) for DSI scores of less than 50 was 4.18 (95% CI, 2.37-7.38; P < .001); for a DSI score of 50 to 80, it was 1.82 (95% CI, 1.10-3.04; P = .02). Compared with people with DDT scores of more than 80, the dementia aHR for DDT scores of less than 50 was 2.66 (95% CI, 1.31-5.42; P = .01); for a DDT score of 50 to 80, it was 2.40 (95% CI, 1.45-3.98; P = .001). The AD results were similar. Pure tone averages were weakly and insignificantly associated with dementia and AD, and associations were null when controlling for DSI scores.

Conclusions and Relevance

In this cohort study, abnormal central auditory processing as measured by dichotic tests was independently associated with dementia and AD risk.

Speech Understanding in Modulated Noise and Speech Maskers as a Function of Cognitive Status in Older Adults

Objectives The purpose of this study was to investigate the impact of different types of maskers on speech understanding as a function of cognitive status in older adults. The hypothesis tested was that individuals with a diagnosis of mild cognitive impairment (MCI) or mild dementia would perform like their age- and hearing status-matched control counterparts in modulated noise but would perform more poorly in the presence of competing speech. Design Participants (n = 39; age range: 55-77 years old) performed a speech-in-noise task and completed two cognitive screening tests and a measure of working memory. Sentences were presented in the presence of two types of maskers (i.e., speech envelope-modulated noise and two-talker, same-sex competing speech). Two analyses were undertaken: (a) a between-groups comparison of individuals diagnosed with MCI/dementia, individuals who failed both cognitive screeners (possible MCI), and age- and hearing status-matched neurologically healthy control individuals and (b) a mixed-model analysis of variance of speech perception performance as a function of working memory capacity. Results The between-groups comparison yielded significant group differences for speech understanding in both masking conditions, with the MCI/dementia group performing more poorly than the neurologically healthy controls and possible MCI groups. A single measure of working memory (Size Comparison Span [SICSPAN]) was correlated with performance on the speech perception task in the competing speech conditions. Conclusions Adults with a diagnosis of MCI or mild dementia performed more poorly on a speech perception task than their age- and hearing status-matched control counterparts in the presence of both maskers, with larger group mean differences when the target speech was presented in a two-talker masker. This suggests increased difficulty understanding speech in the presence of distracting backgrounds for people with MCI/dementia. Future studies should consider how to target this potentially vulnerable population as they may be experiencing increased difficulty communicating in challenging environments.

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.

Open science datasets from PREVENT-AD, a longitudinal cohort of pre-symptomatic Alzheimer's disease

To move Alzheimer Disease (AD) research forward it is essential to collect data from large cohorts, but also make such data available to the global research community. We describe the creation of an open science dataset from the PREVENT-AD (PResymptomatic EValuation of Experimental or Novel Treatments for AD) cohort, composed of cognitively unimpaired older individuals with a parental or multiple-sibling history of AD. From 2011 to 2017, 386 participants were enrolled (mean age 63 years old ± 5) for sustained investigation among whom 349 have retrospectively agreed to share their data openly. Repositories are findable through the unified interface of the Canadian Open Neuroscience Platform and contain up to five years of longitudinal imaging data, cerebral fluid biochemistry, neurosensory capacities, cognitive, genetic, and medical information. Imaging data can be accessed openly at https://openpreventad.loris.ca while most of the other information, sensitive by nature, is accessible by qualified researchers at https://registeredpreventad.loris.ca. In addition to being a living resource for continued data acquisition, PREVENT-AD offers opportunities to facilitate understanding of AD pathogenesis.

Interacting effects of frontal lobe neuroanatomy and working memory capacity to older listeners' speech recognition in noise

Many older adults are struggling with understanding spoken language, particularly when background noise interferes with comprehension. In the present study, we investigated a potential interaction between two well-known factors associated with greater speech-in-noise (SiN) reception thresholds in older adults, namely a) lower working memory capacity and b) age-related structural decline of frontal lobe regions. In a sample of older adults (N = 25) and younger controls (N = 13) with normal pure-tone thresholds, SiN reception thresholds and working memory capacity were assessed. Furthermore, T1-weighted structural MR-images were recorded to analyze neuroanatomical traits (i.e., cortical thickness (CT) and cortical surface area (CSA)) of the cortex. As expected, the older group showed greater SiN reception thresholds compared to the younger group. We also found consistent age-related atrophy (i.e., lower CT) in brain regions associated with SiN recognition, namely the superior temporal lobe bilaterally, the right inferior frontal and precentral gyrus, as well as the left superior frontal gyrus. Those older participants with greater atrophy in these brain regions showed greater SiN reception thresholds. Interestingly, the association between CT in the left superior frontal gyrus and SiN reception thresholds was moderated by individual working memory capacity. Older adults with greater working memory capacity benefitted more strongly from thicker frontal lobe regions leading to better SiN recognition. Overall, our results fit well into the literature showing that age-related structural decline in auditory- and cognition-related brain areas is associated with greater SiN reception thresholds in older adults. However, we highlight that this association changes as a function of individual working memory capacity. We therefore believe that future interventions to improve SiN recognition in older adults should take into account the role of the frontal lobe as well as individual working memory capacity.

Cognitive Flexibility and Inhibition in Individuals with Age-Related Hearing Loss

Growing evidence suggests alterations in cognitive control processes in individuals with varying degrees of age-related hearing loss (ARHL); however, alterations in those with unaided mild ARHL are understudied. The current study examined two cognitive control processes, cognitive flexibility, and inhibition, in 21 older adults with unaided mild ARHL and 18 age- and education-matched normal hearing (NH) controls. All participants underwent comprehensive audiological and cognitive evaluations including Trail Making Test-B, Verbal Fluency, Stroop, and two Go/NoGo tasks. Group differences in cognitive flexibility and inhibition as well as associations between peripheral and central hearing ability and measures of cognitive flexibility and inhibition were investigated. Findings revealed that the ARHL group took significantly longer to complete the Stroop task and had higher error rates on NoGo trials on both Go/NoGo tasks relative to the NH controls. Additionally, poorer peripheral and central hearing were associated with poorer cognitive flexibility and inhibitory control. Our findings suggest slower and more inefficient inhibitory control in the mild ARHL group relative to the NH group and add to decades of research on the association between hearing and cognition.

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.

The connectivity between the olfactory and auditory cortex predicts an individual's sleep quality

Sleep disorders and multiple sensory impairments have been noticed as the potential first sign of neurodegenerative diseases such as the Parkinson disease. The relationship between sleep quality and the sensory neural basis would help us consider their combination in early diagnosis. In the present study, 32 out of 45 healthy subjects' resting-state functional magnetic resonance imaging data survived from motion correction and entered into the connectivity analysis. We found that the connectivity between two regions of interest (the left olfactory gyrus and the left superior temporal pole) and the regional homogeneity in the left middle temporal gyrus were negatively correlated with their Pittsburgh sleep quality index. These results suggest that these sensory-related brain regions are related to sleep quality and they may together predict the diseases.

Hearing loss is associated with gray matter differences in older adults at risk for and with Alzheimer's disease

Using data from the COMPASS-ND study we investigated associations between hearing loss and hippocampal volume as well as cortical thickness in older adults with subjective cognitive decline (SCD), mild cognitive impairment (MCI), and Alzheimer's dementia (AD). SCD participants with greater pure-tone hearing loss exhibited lower hippocampal volume, but more cortical thickness in the left superior temporal gyrus and right pars opercularis. Greater speech-in-noise reception thresholds were associated with lower cortical thickness bilaterally across much of the cortex in AD. The AD group also showed a trend towards worse speech-in-noise thresholds compared to the SCD group.

"The Dichotic Digit Test" as an Index Indicator for Hearing Problem in Dementia: Systematic Review and Meta-Analysis

BACKGROUND

Patients with dementia commonly have problems processing speech in the presence of competing background speech or noise. This difficulty can be present from the very early stages of dementia, and may be a preclinical feature of Alzheimer's disease.

PURPOSE

This study investigates whether people with dementia perform worse on the dichotic digit test (DDT), an experimental probe of speech processing in the presence of competing speech, and whether test performance may predict dementia onset.

RESEARCH DESIGN

Systematic review and meta-analysis.

DATA COLLECTION AND ANALYSIS

A literature search was conducted in Medline, Embase, Scopus, and Psycinfo. We included (1) studies that included people with a diagnosis of dementia and a healthy control group with no cognitive impairment; (2) studies that reported results from a DDT in a free-recall response task; and (3) studies that had the dichotic digit mean correct percentage score or right-ear advantage, as outcome measurements.

RESULTS

People with dementia had a lower DDT total score, with a pooled mean difference of 18.6% (95% confidence interval [CI]: 21.2-15.9). Patients with dementia had an increased right-ear advantage relative to controls with a pooled difference of 24.4% (95% CI: 21.8-27.0).

CONCLUSION

The DDT total scores are lower and the right-ear advantage increased in cognitively impaired versus normal control participants. The findings also suggest that the reduction of dichotic digit total score and increase of right-ear advantage progress as cognitive impairment increases. Whether abnormalities in dichotic digit scores could predict subsequent dementia onset should be examined in further longitudinal studies.

The Peripheral Hearing and Central Auditory Processing Skills of Individuals With Subjective Memory Complaints

Purpose

This study examined the central auditory processing (CAP) assessment results of adults between 45 and 85 years of age with probable pre-clinical Alzheimer’s disease – i.e., individuals with subjective memory complaints (SMCs) as compared to those who were not reporting significant levels of memory complaints (non-SMCs). It was hypothesized that the SMC group would perform significantly poorer on tests of central auditory skills compared to participants with non-SMCs (control group).

Methods

A total of 95 participants were recruited from the larger Western Australia Memory Study and were classified as SMCs (N = 61; 20 males and 41 females, mean age 71.47 ±7.18 years) and non-SMCs (N = 34; 10 males, 24 females, mean age 68.85 ±7.69 years). All participants completed a peripheral hearing assessment, a CAP assessment battery including Dichotic Digits, Duration Pattern Test, Dichotic Sentence Identification, Synthetic Sentence Identification with Ipsilateral Competing Message (SSI-ICM) and the Quick-Speech-in-Noise, and a cognitive screening assessment.

Results

The SMCs group performed significantly poorer than the control group on SSI-ICM −10 and −20 dB signal-to-noise conditions. No significant differences were found between the two groups on the peripheral hearing threshold measurements and other CAP assessments.

Conclusions

The results suggest that individuals with SMCs perform poorly on specific CAP assessments in comparison to the controls. The poor CAP in SMC individuals may result in a higher cost to their finite pool of cognitive resources. The CAP results provide yet another biomarker that supports the hypothesis that SMCs may be a primary indication of neuropathological changes in the brain. Longitudinal follow up of individuals with SMCs, and decreased CAP abilities should inform whether this group is at higher risk of developing dementia as compared to non-SMCs and those SMC individuals without CAP difficulties.

Lost in sound: auditory perceptual abilities in neurodegenerative diseases

This scientific commentary refers to ‘Impairments of auditory scene analysis in posterior cortical atrophy’, by Hardy et al. (doi:10.1093/brain/awaa221).

Auditory impairment in H-ABC tubulinopathy

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a neurodegenerative disease due to mutations in TUBB4A. Patients suffer from extrapyramidal movements, spasticity, ataxia, and cognitive deficits. Magnetic resonance imaging features are hypomyelination and atrophy of the striatum and cerebellum. A correlation between the mutations and their cellular, tissue and organic effects is largely missing. The effects of these mutations on sensory functions have not been described so far. We have previously reported a rat carrying a TUBB4A (A302T) mutation and sharing most of the clinical and radiological signs with H-ABC patients. Here, for the first time, we did a comparative study of the hearing function in an H-ABC patient and in this mutant model. By analyzing hearing function, we found that there are no significant differences in the auditory brainstem response (ABR) thresholds between mutant rats and WT controls. Nevertheless, ABRs show longer latencies in central waves (II-IV) that in some cases disappear when compared to WT. The patient also shows abnormal AEPs presenting only Waves I and II. Distortion product of otoacoustic emissions and immunohistochemistry in the rat show that the peripheral hearing function and morphology of the organ of Corti are normal. We conclude that the tubulin mutation severely impairs the central hearing pathway most probably by progressive central white matter degeneration. Hearing function might be affected in a significant fraction of patients with H-ABC; therefore, screening for auditory function should be done on patients with tubulinopathies to evaluate hearing support therapies.

Narrative Review of Sensory Changes as a Biomarker for Alzheimer's Disease

Early recognition of Alzheimer's disease (AD) in the prodromal period has not been robust yet will be necessary if effective disease-modifying drugs are to be useful in preventing or delaying the condition. The objective of this narrative review was to describe the current, evidenced based understanding of alterations in sensory data as potential biomarkers for AD. Review of empirical studies that tested senses as biomarkers for AD and were published in English within the past 50 years was completed. Eighteen empirical studies were identified that met the strict criteria for inclusion, with 12 of these studies being related to the olfactory system. Two studies examined auditory, two examined vision, one examined proprioception, and one examined taste. Thus, only olfaction has been studied to any extent, leaving a clear gap in the literature for the use of other senses. A promising area of research has begun to be reported concerning differences in responses to pain stimuli in AD relative to cognitively normal subjects. Pain is not a single sense like the others but integrates several senses and may allow for use as an early biomarker for AD, as it integrates several brain areas and pathways. Unlike the other senses, simple devices can be used to measure changes in pain perception in cognitively normal adults with genetic predispositions for possible AD, making this potentially useful for clinicians in the future.

5XFAD mice show early-onset gap encoding deficits in the auditory cortex

Early detection will be crucial for effective treatment or prevention of Alzheimer's disease. The identification and validation of early, noninvasive biomarkers is therefore key to avoiding the most devastating aspects of Alzheimer's disease. Measures of central auditory processing such as gap detection have recently emerged as potential biomarkers in both human patients and the 5XFAD mouse model of Alzheimer's disease. Full validation of gap detection deficits as a biomarker will require detailed understanding of the underlying neuropathology, including which brain structures are involved and how the operation of neural circuits is affected. Here we show that 5XFAD mice exhibit gap detection deficits as early as 2 months of age, well before development of Alzheimer's disease-associated pathology. We then examined responses of neurons in the auditory cortex to gaps in white noise. Both gap responses and baseline firing rates were robustly and progressively degraded in 5XFAD mice compared to littermate controls. These impairments were first evident at 2-4 months of age in males, and 4-6 months in females. This demonstrates early-onset impairments to the central auditory system, which could be due to damage in the auditory cortex, upstream subcortical structures, or both.

Alzheimer disease starts in childhood in polluted Metropolitan Mexico City. A major health crisis in progress

Exposures to fine particulate matter (PM_2.5) and ozone (O₃) above USEPA standards are associated with Alzheimer's disease (AD) risk. Metropolitan Mexico City (MMC) youth have life time exposures to PM_2.5 and O₃ above standards. We focused on MMC residents ≤30 years and reviewed 134 consecutive autopsies of subjects age 20.03 ± 6.38 y (range 11 months to 30 y), the staging of Htau and ß amyloid, the lifetime cumulative PM_2.5 (CPM _2.5) and the impact of the Apolipoprotein E (APOE) 4 allele, the most prevalent genetic risk for AD. We also reviewed the results of the Montreal Cognitive Assessment (MoCA) and the brainstem auditory evoked potentials (BAEPs) in clinically healthy young cohorts. Mobile sources, particularly from non-regulated diesel vehicles dominate the MMC pollutant emissions exposing the population to PM_2.5 concentrations above WHO and EPA standards. Iron-rich,magnetic, highly oxidative, combustion and friction-derived nanoparticles (CFDNPs) are measured in the brain of every MMC resident. Progressive development of Alzheimer starts in childhood and in 99.25% of 134 consecutive autopsies ≤30 years we can stage the disease and its progression; 66% of ≤30 years urbanites have cognitive impairment and involvement of the brainstem is reflected by auditory central dysfunction in every subject studied. The average age for dementia using MoCA is 20.6 ± 3.4 y. APOE4 vs 3 carriers have 1.26 higher odds of committing suicide. PM_2.5 and CFDNPs play a key role in the development of neuroinflammation and neurodegeneration in young urbanites. A serious health crisis is in progress with social, educational, judicial, economic and overall negative health impact for 25 million residents. Understanding the neural circuitry associated with the earliest cognitive and behavioral manifestations of AD is needed. Air pollution control should be prioritised-including the regulation of diesel vehicles- and the first two decades of life ought to be targeted for neuroprotective interventions. Defining paediatric environmental, nutritional, metabolic and genetic risk factor interactions is a multidisciplinary task of paramount importance to prevent Alzheimer's disease. Current and future generations are at risk.

Hearing handicap in Asian patients with dementia

BACKGROUND

Hearing loss and hearing handicap may contribute to cognitive impairment and dementia. The purpose of this study was to analyze the association between hearing loss and hearing handicap with dementia in an Asian memory clinic parents.

METHODS

This study includes the data obtained from patients with mild dementia who attended the National University hospital memory clinic and non-demented healthy subjects among spouses and caregivers who are non-genetically related to our patients. All participants underwent comprehensive physical, medical, neuropsychological and audiological assessments (i.e. pure tone audiometry - PTA). Disabling hearing loss was defined as a hearing loss of >40 dB in the better ear on PTA. Amsterdam Inventory for Auditory Disability and Handicap (AIADH) questionnaire was administered through the verbal interview to measure their hearing handicap score. Linear regression models were used to investigate the association between hearing loss and hearing handicap with dementia. Mean differences (β) with 95% confidence intervals (CI) were calculated.

RESULTS

91 participants (65-90 years old) were recruited for this study; 39 of them were patients with dementia and 52 were non-demented healthy controls. 48.7% of the patients with dementia had disabling hearing loss, which is higher than the non-demented controls (25.0%) (p = 0.019). The significant association between hearing handicap (as measured by AIADH) and dementia was observed, which was independent of demographic factors and audiology related history and PTA average (β = -6.40; 95% CI =0.11.99, -0.81, p = 0.025). There was no independent association between hearing loss and dementia (p > 0.05).

CONCLUSION

A significant association between hearing handicap and dementia was found. The mechanism of this association requires further research and may involve higher order central processing disorder.

Pure tone audiometry and cerebral pathology in healthy older adults

BACKGROUND

Hearing impairment may be a modifiable risk factor for dementia. However, it is unclear how hearing associates with pathologies relevant to dementia in preclinical populations.

METHODS

Data from 368 cognitively healthy individuals born during 1 week in 1946 (age range 69.2-71.9 years), who underwent structural MRI, ¹⁸F-florbetapir positron emission tomography, pure tone audiometry and cognitive testing as part of a neuroscience substudy the MRC National Survey of Health and Development were analysed. The aim of the analysis was to investigate whether pure tone audiometry performance predicted a range of cognitive and imaging outcomes relevant to dementia in older adults.

RESULTS

There was some evidence that poorer pure tone audiometry performance was associated with lower primary auditory cortex thickness, but no evidence that it predicted in vivo β-amyloid deposition, white matter hyperintensity volume, hippocampal volume or Alzheimer's disease-pattern cortical thickness. A negative association between pure tone audiometry and mini-mental state examination score was observed, but this was no longer evident after excluding a test item assessing repetition of a single phrase.

CONCLUSION

Pure tone audiometry performance did not predict concurrent β-amyloid deposition, small vessel disease or Alzheimer's disease-pattern neurodegeneration, and had limited impact on cognitive function, in healthy adults aged approximately 70 years.

Exploratory study of the teaching of neuropsychology in the curricula of undergraduate courses in Speech-Language Pathology

PURPOSE

To determine the level of teaching of neuropsychology within undergraduate courses of speech-language pathology in Brazil using an exploratory document analysis of the curricula of the undergraduate courses.

METHODS

It is a quantitative exploratory document analysis. A review of available documents from websites and/or received from course directors (pedagogical course project, course content, and/or syllabus) of public and private universities in Brazil was carried out. Using an agreed consensus checklist, 3 researchers verified which universities offered subjects on neuropsychology by means of a search for the term 'neuropsychology' or neuropsychological'. Associations between type of university and region and the provision of neuropsychology courses were also explored.

RESULTS

72 universities were included in the study and only nine of them offered subjects on neuropsychology. None of the associations tested was statistically significant.

CONCLUSION

The provision of neuropsychology for speech-language pathology undergraduate students is limited, and not associated with the type of university, the year of the pedagogical course project, or the region in which the university is located. The findings call attention to the need to adapt undergraduate curricula in speech-language pathology to consider the entire scope of this profession and address the epidemiology of communication disorders.

Impaired memory-guided attention in asymptomatic APOE4 carriers

Attention and memory may be impaired in individuals at-risk for Alzheimer's disease (AD), though standard cognitive assessments typically study the two in parallel. In reality, attention and memory interact to facilitate information processing, and thus a more integrative approach is required. Here, we used a novel auditory paradigm to assess how long-term memory for auditory scenes facilitates detection of an auditory target in asymptomatic carriers of Apolipoprotein E4 (APOE4), the principle risk gene for late-onset AD. We tested 60 healthy middle-aged adults with varying doses of APOE4 - 20 APOE4 homozygotes (E4/E4), 20 heterozygotes (E3/E4) and 20 non-carriers (E3/E3) - to determine effect on memory-guided attention. While explicit memory was unaffected by genotype, APOE4 dose significantly impaired memory-guided attention. A relationship between explicit memory and memory-guided attention was observed in non-carriers, but this correlation was not significant in E3/E4 and E4/E4 carriers, suggesting that APOE4 carriers rely less on explicit memory to facilitate attention. Since memory-guided attention declined with age in APOE4 homozygotes, this impairment may reflect early disease rather than being a life-long trait. In sum, asymptomatic individuals at increased genetic risk of AD show an age-dependent decline in attention-memory interaction when memory alone is not impaired.

5XFAD Mice Show Early Onset Gap Detection Deficits

Alzheimer's patients show auditory temporal processing deficits very early in disease progression, before the onset of major cognitive impairments. In addition to potentially contributing to speech perception and communication deficits in patients, this also represents a potential early biomarker for Alzheimer's. For this reason, tests of temporal processing such as gap detection have been proposed as an early diagnosis tool. For a biomarker such as gap detection deficits to have maximum clinical value, it is important to understand what underlying neuropathology it reflects. For example, temporal processing deficits could arise from alterations at cortical, midbrain, or brainstem levels. Mouse models of Alzheimer's disease can provide the ability to reveal in detail the molecular and circuit pathology underlying disease symptoms. Here we tested whether 5XFAD mice, a leading Alzheimer's mouse model, exhibit impaired temporal processing. We found that 5XFAD mice showed robust gap detection deficits. Gap detection deficits were first detectable at about 2 months of age and became progressively worse, especially for males and for longer gap durations. We conclude that 5XFAD mice are well-suited to serve as a model for understanding the circuit mechanisms that contribute to Alzheimer's-related gap detection deficits.

Auditory system dysfunction in Alzheimer disease and its prodromal states: A review

Recent findings suggest that both peripheral and central auditory system dysfunction occur in the prodromal stages of Alzheimer Disease (AD), and therefore may represent early indicators of the disease. In addition, loss of auditory function itself leads to communication difficulties, social isolation and poor quality of life for both patients with AD and their caregivers. Developing a greater understanding of auditory dysfunction in early AD may shed light on the mechanisms of disease progression and carry diagnostic and therapeutic importance. Herein, we review the literature on hearing abilities in AD and its prodromal stages investigated through methods such as pure-tone audiometry, dichotic listening tasks, and evoked response potentials. We propose that screening for peripheral and central auditory dysfunction in at-risk populations is a low-cost and effective means to identify early AD pathology and provides an entry point for therapeutic interventions that enhance the quality of life of AD patients.