Functional Connectivity of Heschl's Gyrus Associated With Age-Related Hearing Loss: A Resting-State fMRI Study

Exploring timescale-specific functional brain networks and their associations with aging and cognitive performance in a healthy cohort without dementia

INTRODUCTION

Functional brain networks (FBNs) coordinate brain functions and are studied in fMRI using blood-oxygen-level-dependent (BOLD) signal correlations. Previous research links FBN changes to aging and cognitive decline, but various physiological factors influnce BOLD signals. Few studies have investigated the intrinsic components of the BOLD signal in different timescales using signal decomposition. This study aimed to explore differences between intrinsic FBNs and traditional BOLD-FBN, examining their associations with age and cognitive performance in a healthy cohort without dementia.

MATERIALS AND METHODS

A total of 396 healthy participants without dementia (men = 157; women = 239; age range = 20-85 years) were enrolled in this study. The BOLD signal was decomposed into several intrinsic signals with different timescales using ensemble empirical mode decomposition, and FBNs were constructed based on both the BOLD and intrinsic signals. Subsequently, network features-global efficiency and local efficiency values-were estimated to determine their relationship with age and cognitive performance.

RESULTS

The findings revealed that the global efficiency of traditional BOLD-FBN correlated significantly with age, with specific intrinsic FBNs contributing to these correlations. Moreover, local efficiency analysis demonstrated that intrinsic FBNs were more meaningful than traditional BOLD-FBN in identifying brain regions related to age and cognitive performance.

CONCLUSIONS

These results underscore the importance of exploring timescales of BOLD signals when constructing FBN and highlight the relevance of specific intrinsic FBNs to aging and cognitive performance. Consequently, this decomposition-based FBN-building approach may offer valuable insights for future fMRI studies.

Sound-localization-related activation and functional connectivity of dorsal auditory pathway in relation to demographic, cognitive, and behavioral characteristics in age-related hearing loss

Background

Patients with age-related hearing loss (ARHL) often struggle with tracking and locating sound sources, but the neural signature associated with these impairments remains unclear.

Materials and methods

Using a passive listening task with stimuli from five different horizontal directions in functional magnetic resonance imaging, we defined functional regions of interest (ROIs) of the auditory "where" pathway based on the data of previous literatures and young normal hearing listeners (n = 20). Then, we investigated associations of the demographic, cognitive, and behavioral features of sound localization with task-based activation and connectivity of the ROIs in ARHL patients (n = 22).

Results

We found that the increased high-level region activation, such as the premotor cortex and inferior parietal lobule, was associated with increased localization accuracy and cognitive function. Moreover, increased connectivity between the left planum temporale and left superior frontal gyrus was associated with increased localization accuracy in ARHL. Increased connectivity between right primary auditory cortex and right middle temporal gyrus, right premotor cortex and left anterior cingulate cortex, and right planum temporale and left lingual gyrus in ARHL was associated with decreased localization accuracy. Among the ARHL patients, the task-dependent brain activation and connectivity of certain ROIs were associated with education, hearing loss duration, and cognitive function.

Conclusion

Consistent with the sensory deprivation hypothesis, in ARHL, sound source identification, which requires advanced processing in the high-level cortex, is impaired, whereas the right-left discrimination, which relies on the primary sensory cortex, is compensated with a tendency to recruit more resources concerning cognition and attention to the auditory sensory cortex. Overall, this study expanded our understanding of the neural mechanisms contributing to sound localization deficits associated with ARHL and may serve as a potential imaging biomarker for investigating and predicting anomalous sound localization.

Long-term follow-up of brain regional changes and the association with cognitive impairment in quarantined COVID-19 survivors

OBJECTIVE

This study aimed to evaluate the neuropsychiatric symptoms of quarantined COVID-19 survivors 15 months after discharge and explore its potential association with structural and functional brain changes and inflammation.

METHODS

A total of 51 quarantined COVID-19 survivors and 74 healthy controls were included in this study. Cognitive function was assessed using the THINC-integrated tool. Structural brain changes were examined through both surface- and volume-based analyses, and functional changes were assessed using resting-state amplitude low-frequency fluctuation (ALFF). Serum inflammatory markers were measured by a multiplexed flow cytometric assay.

RESULTS

COVID-19 survivors exhibited subjective cognitive decline compared to healthy controls, despite no significant differences in objective cognitive tasks. Structural analysis revealed significantly increased gray matter volume and cortical surface area in the left transverse temporal gyrus (Heschl's gyrus) in quarantined COVID-19 survivors. This enlargement was negatively correlated with cognitive impairment. The ALFF analysis showed decreased neural activity in multiple brain regions. Elevated levels of serum inflammatory markers were also found in COVID-19 survivors, including MIP-1a, MIP-1b, TNF-a, and IL-8, which correlated with functional abnormalities.

CONCLUSIONS

Our findings indicate a subjective cognitive decline in quarantined COVID-19 survivors 15 months after discharge, which is associated with brain structural alterations in the left Heschl's gyrus. The observed elevation of inflammatory markers suggests a potential mechanism involving inflammation-induced neurogenesis. These results contribute to our understanding of the possible mechanisms underlying long-term neuropsychiatric consequences of COVID-19 and highlight the need for further research to develop targeted interventions.

Abnormal white and gray matter functional connectivity is associated with cognitive dysfunction in presbycusis

Presbycusis is characterized by high-frequency hearing loss and is closely associated with cognitive decline. Previous studies have observed functional reorganization of gray matter in presbycusis, but the information transmission between gray matter and white matter remains ill-defined. Using resting-state functional magnetic resonance imaging, we investigated differences in functional connectivity (GM-GM, WM-WM, and GM-WM) between 60 patients with presbycusis and 57 healthy controls. Subsequently, we examined the correlation between these connectivity differences with high-frequency hearing loss as well as cognitive impairment. Our results revealed significant alterations in functional connectivity involving the body of the corpus callosum, posterior limbs of the internal capsule, retrolenticular region of the internal capsule, and the gray matter regions in presbycusis. Notably, disrupted functional connectivity was observed between the body of the corpus callosum and ventral anterior cingulate cortex in presbycusis, which was associated with impaired attention. Additionally, enhanced functional connectivity was found in presbycusis between the internal capsule and the ventral auditory processing stream, which was related to impaired cognition in multiple domains. These two patterns of altered functional connectivity between gray matter and white matter may involve both bottom-up and top-down regulation of cognitive function. These findings provide novel insights into understanding cognitive compensation and resource redistribution mechanisms in presbycusis.

Compensation in neuro-system related to age-related hearing loss

BACKGROUND

Age-related hearing loss (ARHL) is a major cause of chronic disability among the elderly. Individuals with ARHL not only have trouble hearing sounds, but also with speech perception. As the perception of auditory information is reliant on integration between widespread brain networks to interpret auditory stimuli, both auditory and extra-auditory systems which mainly include visual, motor and attention systems, play an important role in compensating for ARHL.

OBJECTIVES

To better understand the compensatory mechanism of ARHL and inspire better interventions that may alleviate ARHL.

METHODS

We mainly focus on the existing information on ARHL-related central compensation. The compensatory effects of hearing aids (HAs) and cochlear implants (CIs) on ARHL were also discussed.

RESULTS

Studies have shown that ARHL can induce cochlear hair cell damage or loss and cochlear synaptopathy, which could induce central compensation including compensation of auditory and extra-auditory neural networks. The use of HAs and CIs can improve bottom-up processing by enabling 'better' input to the auditory pathways and then to the cortex by enhancing the diminished auditory signal.

CONCLUSIONS

The central compensation of ARHL and its possible correlation with HAs and CIs are current hotspots in the field and should be given focus in future research.

Exploring Successful Cognitive Aging: Insights Regarding Brain Structure, Function, and Demographics

In the realm of cognitive science, the phenomenon of "successful cognitive aging" stands as a hallmark of individuals who exhibit cognitive abilities surpassing those of their age-matched counterparts. However, it is paramount to underscore a significant gap in the current research, which is marked by a paucity of comprehensive inquiries that deploy substantial sample sizes to methodically investigate the cerebral biomarkers and contributory elements underpinning this cognitive success. It is within this context that our present study emerges, harnessing data derived from the UK Biobank. In this study, a highly selective cohort of 1060 individuals aged 65 and above was meticulously curated from a larger pool of 17,072 subjects. The selection process was guided by their striking cognitive resilience, ascertained via rigorous evaluation encompassing both generic and specific cognitive assessments, compared to their peers within the same age stratum. Notably, the cognitive abilities of the chosen participants closely aligned with the cognitive acumen commonly observed in middle-aged individuals. Our study leveraged a comprehensive array of neuroimaging-derived metrics, obtained from three Tesla MRI scans (T1-weighted images, dMRI, and resting-state fMRI). The metrics included image-derived phenotypes (IDPs) that addressed grey matter morphology, the strength of brain network connectivity, and the microstructural attributes of white matter. Statistical analyses were performed employing ANOVA, Mann-Whitney U tests, and chi-square tests to evaluate the distinctive aspects of IDPs pertinent to the domain of successful cognitive aging. Furthermore, these analyses aimed to elucidate lifestyle practices that potentially underpin the maintenance of cognitive acumen throughout the aging process. Our findings unveiled a robust and compelling association between heightened cognitive aptitude and the integrity of white matter structures within the brain. Furthermore, individuals who exhibited successful cognitive aging demonstrated markedly enhanced activity in the cerebral regions responsible for auditory perception, voluntary motor control, memory retention, and emotional regulation. These advantageous cognitive attributes were mirrored in the health-related lifestyle choices of the surveyed cohort, characterized by elevated educational attainment, a lower incidence of smoking, and a penchant for moderate alcohol consumption. Moreover, they displayed superior grip strength and enhanced walking speeds. Collectively, these findings furnish valuable insights into the multifaceted determinants of successful cognitive aging, encompassing both neurobiological constituents and lifestyle practices. Such comprehensive comprehension significantly contributes to the broader discourse on aging, thereby establishing a solid foundation for the formulation of targeted interventions aimed at fostering cognitive well-being among aging populations.

Increased functional connectivity in the right dorsal auditory stream after a full year of piano training in healthy older adults

Learning to play an instrument at an advanced age may help to counteract or slow down age-related cognitive decline. However, studies investigating the neural underpinnings of these effects are still scarce. One way to investigate the effects of brain plasticity is using resting-state functional connectivity (FC). The current study compared the effects of learning to play the piano (PP) against participating in music listening/musical culture (MC) lessons on FC in 109 healthy older adults. Participants underwent resting-state functional magnetic resonance imaging at three time points: at baseline, and after 6 and 12 months of interventions. Analyses revealed piano training-specific FC changes after 12 months of training. These include FC increase between right Heschl's gyrus (HG), and other right dorsal auditory stream regions. In addition, PP showed an increased anticorrelation between right HG and dorsal posterior cingulate cortex and FC increase between the right motor hand area and a bilateral network of predominantly motor-related brain regions, which positively correlated with fine motor dexterity improvements. We suggest to interpret those results as increased network efficiency for auditory-motor integration. The fact that functional neuroplasticity can be induced by piano training in healthy older adults opens new pathways to countervail age related decline.

Functional Organization of Auditory and Reward Systems in Aging

The intrinsic organization of functional brain networks is known to change with age, and is affected by perceptual input and task conditions. Here, we compare functional activity and connectivity during music listening and rest between younger (n = 24) and older (n = 24) adults, using whole-brain regression, seed-based connectivity, and ROI-ROI connectivity analyses. As expected, activity and connectivity of auditory and reward networks scaled with liking during music listening in both groups. Younger adults show higher within-network connectivity of auditory and reward regions as compared with older adults, both at rest and during music listening, but this age-related difference at rest was reduced during music listening, especially in individuals who self-report high musical reward. Furthermore, younger adults showed higher functional connectivity between auditory network and medial prefrontal cortex that was specific to music listening, whereas older adults showed a more globally diffuse pattern of connectivity, including higher connectivity between auditory regions and bilateral lingual and inferior frontal gyri. Finally, connectivity between auditory and reward regions was higher when listening to music selected by the participant. These results highlight the roles of aging and reward sensitivity on auditory and reward networks. Results may inform the design of music-based interventions for older adults and improve our understanding of functional network dynamics of the brain at rest and during a cognitively engaging task.

Women with hearing loss show increased dementia risk and brain atrophy

Hearing loss is a modifiable risk factor for dementia. However, it is unknown whether risk differs by sex. Study 1 used Cox proportional hazard models to examine sex differences in the association between hearing loss (measured by speech-reception thresholds) and dementia risk. Study 2 examined how 2-year changes in hearing is associated with changes in brain volume in auditory-limbic regions. Both studies used UK Biobank data. Women with poor hearing had the greatest risk of dementia, whereas women and men with insufficient hearing were at similar risk. Men with poor hearing did not have increased risk. Presence of social isolation/depressed mood minimally contributed to dementia risk in men and women. Women, but not men, with hearing loss had greater atrophy in auditory and limbic regions compared to normal hearing women and men. Women with hearing loss show greater risk of dementia and brain atrophy, highlighting the need to examine sex-specific mechanisms.

The Impact of Age and Psychosocial Factors on Cognitive and Auditory Outcomes During the COVID-19 Pandemic

PURPOSE

In March 2020, the U.K. government announced that people should isolate to reduce the spread of the virus that causes COVID-19. Outside a pandemic, psychosocial factors, such as socialization and mental health, may impact the relationship between hearing loss and increased dementia risk. We aim to report the impact of psychosocial factors, including social isolation, depression, and engagement in activities, on hearing and cognitive function in younger and older adults during the COVID-19 pandemic.

METHOD

An online survey and experiment assessed self-reported psychosocial factors, self-reported hearing ability and speech-in-noise perception, and cognition. Data were collected between June 2020 and February 2021. Older (n = 112, Mage = 70.08) and younger (n = 121, Mage = 20.52) monolingual speakers of English, without any language or neurological disorders participated. Multiple linear regression models were employed to investigate hypothesized associations between psychosocial factors, and hearing and cognition, in older and younger adults.

RESULTS

Multiple regression analyses indicated that older adults displayed poorer speech-in-noise perception and poorer performance on one of four cognitive tasks, compared with younger adults; increased depression was associated with poorer subjective hearing. Other psychosocial factors did not significantly predict hearing or cognitive function.

CONCLUSIONS

Data suggest that self-reported hearing and depression are related. This conclusion is important for understanding the associations between hearing loss and cognitive decline in the long term, as both hearing loss and depression are risk factors for dementia.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.23810838.

Cognitive reserve disorder in age-related hearing loss: cognitive cortical compensatory to auditory perceptual processing

The aim of this study is to ascertain the mechanisms of cognitive reserve disorder in age-related hearing loss (ARHL), to study the correlation between ARHL and cognitive decline via EEG, and to reverse the adverse remodeling of auditory-cognitive connectivity with hearing aids (HAs). In this study, 32 participants were enrolled, including 12 with ARHLs, 9 with HAs, and 11 healthy controls (HCs), to undergo EEG, Pure Tone Average (PTA), Montreal Cognitive Assessment (MoCA), and other general cognitive tests. There were the lowest MoCA in the ARHL group (P = 0.001), especially in language and abstraction. In the ARHL group, power spectral density of the gamma in right middle temporal gyrus was significantly higher than HC and HA groups, while functional connectivity between superior frontal gyrus and cingulate gyrus was weaker than HC group (P = 0.036) and HA group (P = 0.021). In the HA group, superior temporal gyrus and cuneus had higher connectivity than in the HC group (P = 0.036). In the ARHL group, DeltaTM_DTA (P = 0.042) and CTB (P = 0.011) were more frequent than in the HC group, while there was less DeltaTM_CTA (P = 0.029). PTA was found to be associated with MoCA (r = -0.580) and language (r = -0.572), DeltaTM_CTB had a likewise correlation with MoCA (r = 0.483) and language (r = 0.493), while DeltaTM_DTA was related to abstraction (r = -0.458). Cognitive cortexes compensate for worse auditory perceptual processing in ARHL, which relates to cognitive decline. The impaired functional connectivity between auditory and cognitive cortexes can be remodeled by HAs. DeltaTM may serve as a biomarker for early cognitive decline and decreased auditory speech perception in ARHL.

The effects of exposure to road traffic noise at school on central auditory pathway functional connectivity

As the world becomes more urbanized, more people become exposed to traffic and the risks associated with a higher exposure to road traffic noise increase. Excessive exposure to environmental noise could potentially interfere with functional maturation of the auditory brain in developing individuals. The aim of the present study was to assess the association between exposure to annual average road traffic noise (LAeq) in schools and functional connectivity of key elements of the central auditory pathway in schoolchildren. A total of 229 children from 34 representative schools in the city of Barcelona with ages between 8 and 12 years (49.2% girls) were evaluated. LAeq was obtained as the mean of 2-consecutive day measurements inside classrooms before lessons started following standard procedures to obtain an indicator of long-term road traffic noise levels. A region-of-interest functional connectivity Magnetic Resonance Imaging (MRI) approach was adopted. Functional connectivity maps were generated for the inferior colliculus, medial geniculate body of the thalamus and primary auditory cortex as key levels of the central auditory pathway. Road traffic noise in schools was significantly associated with stronger connectivity between the inferior colliculus and a bilateral thalamic region adjacent to the medial geniculate body, and with stronger connectivity between the medial geniculate body and a bilateral brainstem region adjacent to the inferior colliculus. Such a functional connectivity strengthening effect did not extend to the cerebral cortex. The anatomy of the association implicating subcortical relays suggests that prolonged road traffic noise exposure in developing individuals may accelerate maturation in the basic elements of the auditory pathway. Future research is warranted to establish whether such a faster maturation in early pathway levels may ultimately reduce the developing potential in the whole auditory system.

How can graph theory inform the dual-stream model of speech processing? a resting-state fMRI study of post-stroke aphasia

The dual-stream model of speech processing has been proposed to represent the cortical networks involved in speech comprehension and production. Although it is arguably the prominent neuroanatomical model of speech processing, it is not yet known if the dual-stream model represents actual intrinsic functional brain networks. Furthermore, it is unclear how disruptions after a stroke to the functional connectivity of the dual-stream model's regions are related to specific types of speech production and comprehension impairments seen in aphasia. To address these questions, in the present study, we examined two independent resting-state fMRI datasets: (1) 28 neurotypical matched controls and (2) 28 chronic left-hemisphere stroke survivors with aphasia collected at another site. Structural MRI, as well as language and cognitive behavioral assessments, were collected. Using standard functional connectivity measures, we successfully identified an intrinsic resting-state network amongst the dual-stream model's regions in the control group. We then used both standard functional connectivity analyses and graph theory approaches to determine how the functional connectivity of the dual-stream network differs in individuals with post-stroke aphasia, and how this connectivity may predict performance on clinical aphasia assessments. Our findings provide strong evidence that the dual-stream model is an intrinsic network as measured via resting-state MRI, and that weaker functional connectivity of the hub nodes of the dual-stream network defined by graph theory methods, but not overall average network connectivity, is weaker in the stroke group than in the control participants. Also, the functional connectivity of the hub nodes predicted specific types of impairments on clinical assessments. In particular, the relative strength of connectivity of the right hemisphere's homologues of the left dorsal stream hubs to the left dorsal hubs versus right ventral stream hubs is a particularly strong predictor of post-stroke aphasia severity and symptomology.

Aberrant brain functional network strength related to cognitive impairment in age-related hearing loss

Purpose

Age-related hearing loss (ARHL) is a major public issue that affects elderly adults. However, the neural substrates for the cognitive deficits in patients with ARHL need to be elucidated. This study aimed to explore the brain regions that show aberrant brain functional network strength related to cognitive impairment in patients with ARHL.

Methods

A total of 27 patients with ARHL and 23 well-matched healthy controls were recruited for the present study. Each subject underwent pure-tone audiometry (PTA), MRI scanning, and cognition evaluation. We analyzed the functional network strength by using degree centrality (DC) characteristics and tried to recognize key nodes that contribute significantly. Subsequent functional connectivity (FC) was analyzed using significant DC nodes as seeds.

Results

Compared with controls, patients with ARHL showed a deceased DC in the bilateral supramarginal gyrus (SMG). In addition, patients with ARHL showed enhanced DC in the left fusiform gyrus (FG) and right parahippocampal gyrus (PHG). Then, the bilateral SMGs were used as seeds for FC analysis. With the seed set at the left SMG, patients with ARHL showed decreased connectivity with the right superior temporal gyrus (STG). Moreover, the right SMG showed reduced connectivity with the right middle temporal gyrus (MTG) and increased connection with the left middle frontal gyrus (MFG) in patients with ARHL. The reduced DC in the left and right SMGs showed significant negative correlations with poorer TMT-B scores (r = -0.596, p = 0.002; r = -0.503, p = 0.012, respectively).

Conclusion

These findings enriched our understanding of the neural mechanisms underlying cognitive impairment associated with ARHL and may serve as a potential brain network biomarker for investigating and predicting cognitive difficulties.

Brain Structure and Function Predict Adherence to an Exercise Intervention in Older Adults

INTRODUCTION

Individual differences in brain structure and function in older adults are potential proxies of brain reserve or maintenance and may provide mechanistic predictions of adherence to exercise. We hypothesized that multimodal neuroimaging features would predict adherence to a 6-month randomized controlled trial of exercise in 131 older adults (age, 65.79 ± 4.65 yr, 63% female), alone and in combination with psychosocial, cognitive, and health measures.

METHODS

Regularized elastic net regression within a nested cross-validation framework was applied to predict adherence to the intervention in three separate models (brain structure and function only; psychosocial, health, and demographic data only; and a multimodal model).

RESULTS

Higher cortical thickness in somatosensory and inferior frontal regions and less surface area in primary visual and inferior frontal regions predicted adherence. Higher nodal functional connectivity (degree count) in default, frontoparietal, and attentional networks and less nodal strength in primary visual and temporoparietal networks predicted exercise adherence ( r = 0.24, P = 0.004). Survey and clinical measures of gait and walking self-efficacy, biological sex, and perceived stress also predicted adherence ( r = 0.17, P = 0.056); however, this prediction was not significant when tested against a null test statistic. A combined multimodal model achieved the highest predictive strength ( r = 0.28, P = 0.001).

CONCLUSIONS

Our results suggest that there is a substantial utility of using brain-based measures in future research into precision and individualized exercise interventions older adults.

Longitudinal Changes in Resting-State Functional Connectivity and Gray Matter Volume Are Associated with Conversion to Hearing Impairment in Older Adults

BACKGROUND

Hearing loss was recently identified as a modifiable risk factor for dementia although the potential mechanisms explaining this relationship are unknown.

OBJECTIVE

The current study examined longitudinal change in resting-state fMRI functional connectivity and gray matter volume in individuals who developed a hearing impairment compared to those whose hearing remained normal.

METHODS

This study included 440 participants from the UK Biobank: 163 who had normal hearing at baseline and impaired hearing at follow-up (i.e., converters, mean age = 63.11±6.33, 53% female) and 277 who had normal hearing at baseline and maintained normal hearing at follow-up (i.e., non-converters, age = 63.31±5.50, 50% female). Functional connectivity was computed between a priori selected auditory seed regions (left and right Heschl's gyrus and cytoarchitectonic subregions Te1.0, Te1.1, and Te1.2) and select higher-order cognitive brain networks. Gray matter volume within these same regions was also obtained.

RESULTS

Converters had increased connectivity from left Heschl's gyrus to left anterior insula and from right Heschl's gyrus to right anterior insula, and decreased connectivity between right Heschl's gyrus and right hippocampus, compared to non-converters. Converters also had reduced gray matter volume in left hippocampus and left lateral visual cortex compared to non-converters.

CONCLUSION

These findings suggest that conversion to a hearing impairment is associated with altered brain functional connectivity and gray matter volume in the attention, memory, and visual processing regions that were examined in this study.

Structural Alterations in a Rat Model of Short-Term Conductive Hearing Loss Are Associated With Reduced Resting State Functional Connectivity

Conductive hearing loss (CHL) results in attenuation of air conducted sound reaching the inner ear. How a change in air conducted sound alters the auditory system resulting in cortical alterations is not well understood. Here, we have assessed structural and functional magnetic resonance imaging (MRI) in an adult (P60) rat model of short-term conductive hearing loss (1 week). Diffusion tensor imaging (DTI) revealed fractional anisotropy (FA) and axial diffusivity alterations after hearing loss that circumscribed the auditory cortex (AC). Tractography found the lateral lemniscus tract leading to the bilateral inferior colliculus (IC) was reduced. For baseline comparison, DTI and tractography alterations were not found for the somatosensory cortex. To determine functional connectivity changes due to hearing loss, seed-based analysis (SBA) and independent component analysis (ICA) were performed. Short term conductive hearing loss altered functional connectivity in the AC and IC, but not the somatosensory cortex. The results present an exploratory neuroimaging assessment of structural alterations coupled to a change in functional connectivity after conductive hearing loss. The results and implications for humans consist of structural-functional brain alterations following short term hearing loss in adults.

Screening Tools and Assessment Methods of Cognitive Decline Associated With Age-Related Hearing Loss: A Review

Strong links between hearing and cognitive function have been confirmed by a growing number of cross-sectional and longitudinal studies. Seniors with age-related hearing loss (ARHL) have a significantly higher cognitive impairment incidence than those with normal hearing. The correlation mechanism between ARHL and cognitive decline is not fully elucidated to date. However, auditory intervention for patients with ARHL may reduce the risk of cognitive decline, as early cognitive screening may improve related treatment strategies. Currently, clinical audiology examinations rarely include cognitive screening tests, partly due to the lack of objective quantitative indicators with high sensitivity and specificity. Questionnaires are currently widely used as a cognitive screening tool, but the subject's performance may be negatively affected by hearing loss. Numerous electroencephalogram (EEG) and magnetic resonance imaging (MRI) studies analyzed brain structure and function changes in patients with ARHL. These objective electrophysiological tools can be employed to reveal the association mechanism between auditory and cognitive functions, which may also find biological markers to be more extensively applied in assessing the progression towards cognitive decline and observing the effects of rehabilitation training for patients with ARHL. In this study, we reviewed clinical manifestations, pathological changes, and causes of ARHL and discussed their cognitive function effects. Specifically, we focused on current cognitive screening tools and assessment methods and analyzed their limitations and potential integration.

Age-related hearing loss and cognitive decline: MRI and cellular evidence

Extensive evidence supports the association between age-related hearing loss (ARHL) and cognitive decline. It is, however, unknown whether a causal relationship exists between these two, or whether they both result from shared mechanisms. This paper intends to study this relationship through a comprehensive review of MRI findings as well as evidence of cellular alterations. Our review of structural MRI studies demonstrates that ARHL is independently linked to accelerated atrophy of total and regional brain volumes and reduced white matter integrity. Resting-state and task-based fMRI studies on ARHL also show changes in spontaneous neural activity and brain functional connectivity; and alterations in brain areas supporting auditory, language, cognitive, and affective processing independent of age, respectively. Although MRI findings support a causal relationship between ARHL and cognitive decline, the contribution of potential shared mechanisms should also be considered. In this regard, the review of cellular evidence indicates their role as possible common mechanisms underlying both age-related changes in hearing and cognition. Considering existing evidence, no single hypothesis can explain the link between ARHL and cognitive decline, and the contribution of both causal (i.e., the sensory hypothesis) and shared (i.e., the common cause hypothesis) mechanisms is expected.

Relationship between Memory Load and Listening Demands in Age-Related Hearing Impairment

Age-related hearing loss has been associated with increased recruitment of frontal brain areas during speech perception to compensate for the decline in auditory input. This additional recruitment may bind resources otherwise needed for understanding speech. However, it is unknown how increased demands on listening interact with increasing cognitive demands when processing speech in age-related hearing loss. The current study used a full-sentence working memory task manipulating demands on working memory and listening and studied untreated mild to moderate hard of hearing (n = 20) and normal-hearing age-matched participants (n = 19) with functional MRI. On the behavioral level, we found a significant interaction of memory load and listening condition; this was, however, similar for both groups. Under low, but not high memory load, listening condition significantly influenced task performance. Similarly, under easy but not difficult listening conditions, memory load had a significant effect on task performance. On the neural level, as measured by the BOLD response, we found increased responses under high compared to low memory load conditions in the left supramarginal gyrus, left middle frontal gyrus, and left supplementary motor cortex regardless of hearing ability. Furthermore, we found increased responses in the bilateral superior temporal gyri under easy compared to difficult listening conditions. We found no group differences nor interactions of group with memory load or listening condition. This suggests that memory load and listening condition interacted on a behavioral level, however, only the increased memory load was reflected in increased BOLD responses in frontal and parietal brain regions. Hence, when evaluating listening abilities in elderly participants, memory load should be considered as it might interfere with the assessed performance. We could not find any further evidence that BOLD responses for the different memory and listening conditions are affected by mild to moderate age-related hearing loss.

Neural circuits and behavioral pathways linking hearing loss to affective dysregulation in older adults

Substantial evidence now links age-related hearing loss to incident major depressive disorder in older adults. However, research examining the neural circuits and behavioral mechanisms by which age-related hearing loss leads to depression is at an early phase. It is known that hearing loss has adverse structural and functional brain consequences, is associated with reduced social engagement and loneliness, and often results in tinnitus, which can independently affect cognitive control and emotion processing circuits. While pathways leading from these sequelae of hearing loss to affective dysregulation and depression are intuitive to hypothesize, few studies have yet been designed to provide conclusive evidence for specific pathophysiological mechanisms. Here we review the neurobiological and behavioral consequences of age-related hearing loss, present a model linking them to increased risk for major depressive disorder and suggest how future studies may facilitate the development of rationally designed therapeutic interventions for older adults with impaired hearing to reduce risk for depression and/or ameliorate depressive symptoms.

Aberrant brain functional hubs and causal connectivity in presbycusis

To investigate resting-state connectivity and further understand directional aspects of implicit alterations in presbycusis patients, we used degree centrality (DC) and Granger causality analysis (GCA) to detect functional hubs of the whole-brain network and then analyze directional connectivity. Resting-state functional magnetic resonance imaging (fMRI) scans were performed on 40 presbycusis patients and 40 healthy controls matched for age, gender, and education. We used DC analysis and GCA to characterize abnormal brain networks in presbycusis patients. The associations of network centrality and directed functional connectivity (FC) with clinical measures of presbycusis were also examined according to the above results. We found that the network centrality of left frontal middle gyrus (MFG) was significantly lower than that of healthy control group. Unidirectionally, the left MFG revealed increased directional connectivity to the left superior frontal gyrus (SFG), while the left MFG exhibited decreased directional connectivity to the left middle temporal gyrus (MTG) and right lingual gyrus (LinG). And the decreased directional connectivity was found from the left precentral gyrus (PrCG) to the left MFG. In addition, the Trail-Making Test B (TMT-B) score was negatively correlated with the decreased DC of the left MFG (r = -0.359, p = 0.032). Resting-state fMRI provides a novel method for identifying aberrant brain network architecture. These results primarily indicate altered functional hubs and abnormal frontal lobe connectivity patterns that may further reflect executive dysfunction in patients with presbycusis.

What Can a Child Do With One Normal-Hearing Ear? Speech Perception and Word Learning in Children With Unilateral and Bilateral Hearing Losses Relative to Peers With Normal Hearing

OBJECTIVES

To examine the effects of unilateral hearing loss on children's ability to perceive familiar words and to learn and retain new words. Because children with unilateral hearing loss receive full auditory input in one ear, their performance was expected to be consistent with that of children with normal hearing rather than that of children with moderate bilateral hearing loss.

DESIGN

Participants were 36 school-age children with normal hearing bilaterally, 11 children with moderate bilateral hearing loss, and 11 children with mild-to-profound unilateral hearing loss (six right and five left). Half of the normally hearing children and two-thirds of the children with unilateral hearing loss were from bilingual Spanish/English-speaking homes. One of the 11 children with bilateral hearing loss was from a bilingual Spanish/English-speaking home. All children completed a word recognition test in English and in Spanish, a word-learning task comprised of nonsense words constructed using the phonotactic rules of English, Spanish, and Arabic, and a next-day word-retention test.

RESULTS

Word recognition did not differ across groups in English or Spanish. Learning and retention of nonsense words was highest for the children with normal hearing in all three languages. The children with unilateral and bilateral losses learned and recalled the English nonsense words as well as their normally hearing peers, but performance for the Spanish and Arabic nonsense words was significantly and similarly reduced by hearing loss in either ear.

CONCLUSIONS

Failure to learn and retain new words given a full auditory representation in one ear suggests that children with unilateral and bilateral hearing losses may share a unifying feature of impairment at the level of the central auditory system.

Reduced resting state functional connectivity with increasing age-related hearing loss and McGurk susceptibility

Age-related hearing loss has been related to a compensatory increase in audio-visual integration and neural reorganization including alterations in functional resting state connectivity. How these two changes are linked in elderly listeners is unclear. The current study explored modulatory effects of hearing thresholds and audio-visual integration on resting state functional connectivity. We analysed a large set of resting state data of 65 elderly participants with a widely varying degree of untreated hearing loss. Audio-visual integration, as gauged with the McGurk effect, increased with progressing hearing thresholds. On the neural level, McGurk illusions were negatively related to functional coupling between motor and auditory regions. Similarly, connectivity of the dorsal attention network to sensorimotor and primary motor cortices was reduced with increasing hearing loss. The same effect was obtained for connectivity between the salience network and visual cortex. Our findings suggest that with progressing untreated age-related hearing loss, functional coupling at rest declines, affecting connectivity of brain networks and areas associated with attentional, visual, sensorimotor and motor processes. Especially connectivity reductions between auditory and motor areas were related to stronger audio-visual integration found with increasing hearing loss.

Neural modelling of the semantic predictability gain under challenging listening conditions

When speech intelligibility is reduced, listeners exploit constraints posed by semantic context to facilitate comprehension. The left angular gyrus (AG) has been argued to drive this semantic predictability gain. Taking a network perspective, we ask how the connectivity within language-specific and domain-general networks flexibly adapts to the predictability and intelligibility of speech. During continuous functional magnetic resonance imaging (fMRI), participants repeated sentences, which varied in semantic predictability of the final word and in acoustic intelligibility. At the neural level, highly predictable sentences led to stronger activation of left-hemispheric semantic regions including subregions of the AG (PGa, PGp) and posterior middle temporal gyrus when speech became more intelligible. The behavioural predictability gain of single participants mapped onto the same regions but was complemented by increased activity in frontal and medial regions. Effective connectivity from PGa to PGp increased for more intelligible sentences. In contrast, inhibitory influence from pre-supplementary motor area to left insula was strongest when predictability and intelligibility of sentences were either lowest or highest. This interactive effect was negatively correlated with the behavioural predictability gain. Together, these results suggest that successful comprehension in noisy listening conditions relies on an interplay of semantic regions and concurrent inhibition of cognitive control regions when semantic cues are available.

Eigenvector alignment: Assessing functional network changes in amnestic mild cognitive impairment and Alzheimer's disease

Eigenvector alignment, introduced herein to investigate human brain functional networks, is adapted from methods developed to detect influential nodes and communities in networked systems. It is used to identify differences in the brain networks of subjects with Alzheimer’s disease (AD), amnestic Mild Cognitive Impairment (aMCI) and healthy controls (HC). Well-established methods exist for analysing connectivity networks composed of brain regions, including the widespread use of centrality metrics such as eigenvector centrality. However, these metrics provide only limited information on the relationship between regions, with this understanding often sought by comparing the strength of pairwise functional connectivity. Our holistic approach, eigenvector alignment, considers the impact of all functional connectivity changes before assessing the strength of the functional relationship, i.e. alignment, between any two regions. This is achieved by comparing the placement of regions in a Euclidean space defined by the network’s dominant eigenvectors. Eigenvector alignment recognises the strength of bilateral connectivity in cortical areas of healthy control subjects, but also reveals degradation of this commissural system in those with AD. Surprisingly little structural change is detected for key regions in the Default Mode Network, despite significant declines in the functional connectivity of these regions. In contrast, regions in the auditory cortex display significant alignment changes that begin in aMCI and are the most prominent structural changes for those with AD. Alignment differences between aMCI and AD subjects are detected, including notable changes to the hippocampal regions. These findings suggest eigenvector alignment can play a complementary role, alongside established network analytic approaches, to capture how the brain’s functional networks develop and adapt when challenged by disease processes such as AD.

The Effects of Age-Related Hearing Loss on the Brain and Cognitive Function

Age-related hearing loss (ARHL) is a common problem for older adults, leading to communication difficulties, isolation, and cognitive decline. Recently, hearing loss has been identified as potentially the most modifiable risk factor for dementia. Listening in challenging situations, or when the auditory system is damaged, strains cortical resources, and this may change how the brain responds to cognitively demanding situations more generally. We review the effects of ARHL on brain areas involved in speech perception, from the auditory cortex, through attentional networks, to the motor system. We explore current perspectives on the possible causal relationship between hearing loss, neural reorganisation, and cognitive impairment. Through this synthesis we aim to inspire innovative research and novel interventions for alleviating hearing loss and cognitive decline.