Glucose metabolism in the primary auditory cortex of postlingually deaf patients: an FDG-PET study

Distinct changes in brain metabolism in patients with dementia and hearing loss

INTRODUCTION

Previous studies have reported that hearing loss (HL) is associated with dementia, although the mechanistic underpinnings remain elusive. This study aimed to evaluate the changes in brain metabolism in patients with HL and different types of dementia.

METHODS

Patients with cognitive impairment (CI) and HL treated at the university-based memory clinic from May 2016 to October 2021 were included. In total, 108 patients with CI and HL prospectively underwent audiometry, neuropsychological test, magnetic resonance imaging, and 18 F-fluorodeoxyglucose positron emission tomography. Twenty-seven individuals without cognitive impairment and hearing loss were enrolled as a control group. Multivariable regression was performed to evaluate brain regions correlated with each pathology type after adjusting for confounding factors.

RESULTS

Multivariable regression analyses revealed that Alzheimer's disease-related CI (ADCI) was associated with hypometabolic changes in the right superior temporal gyrus (STG), right middle temporal gyrus (MTG), and bilateral medial temporal lobe. Lewy body disease-related CI (LBDCI) and vascular CI were associated with hypermetabolic and hypometabolic changes in the ascending auditory pathway, respectively. In the pure ADCI group, the degree of HL was positively associated with abnormal increase of brain metabolism in the right MTG, whereas it was negatively associated with decreased brain metabolism in the right STG in the pure LBDCI group.

CONCLUSION

Each dementia type is associated with distinct changes in brain metabolism in patients with HL.

Characteristics of brain glucose metabolism and metabolic connectivity in noise-induced hearing loss

The purpose of this study was to evaluate the differences in cerebral glucose metabolism and metabolic connectivity between noise-induced hearing loss (NIHL) subjects and normal subjects. Eighty-nine subjects who needed close observation for NIHL or were diagnosed with NIHL and 89 normal subjects were enrolled. After pre-processing of positron emission tomography images including co-registration, spatial normalization, and smoothing, a two-sample t-test was conducted to compare cerebral glucose metabolism between the two groups. To evaluate metabolic connectivity between two groups, BRAPH-BRain Analysis using graPH theory, a software package to perform graph theory analysis of the brain connectome was used. NIHL subjects showed hypometabolism compared to normal subjects in both insulae (x - 38, y - 18, z 4; × 42, y - 12, z 4) and right superior temporal gyrus (× 44, y 16, z - 20). No brain regions showed hypermetabolism in the NIHL subjects. In metabolic connectivity analysis, NIHL subjects showed decreased average strength, global efficiency, local efficiency, and mean clustering coefficient when compared with normal subjects. Decreased glucose metabolism and metabolic connectivity in NIHL subject might reflect decreased auditory function. It might be characteristic of sensorineural hearing loss.

Speech Perception of Second Cochlear Implant after 6 Years of Age in Prelingually Deaf Children

Sequential bilateral cochlear implantation in children becomes less effective as the inter-implant interval increases. However, the cause of this and the age at which speech perception becomes impossible are unclear. We examined the cases of 11 prelingually deaf children who underwent unilateral cochlear implantation at our hospitals before the age of 5 years old, followed by a second implantation procedure on the contralateral side when they were aged ≥ 6 years old (6-12 years old). The subjects' hearing thresholds and speech discrimination scores for the second cochlear implant were evaluated at 3 postoperative months and 1-7 years. All of the subjects demonstrated improvements in their hearing thresholds to a mean of 30 dB HL at 1 year. Regarding speech perception, one patient (a 12-year-old), who had developed bilateral hearing loss at 30 months of age after contracting mumps, demonstrated a 90% improvement in his speech discrimination score at 1 year. However, among the other congenitally deaf children, there were two patients whose speech discrimination scores had improved by ≥ 80% at > 4 postoperative years. The congenitally deaf children exhibited poor speech perception despite showing improved hearing thresholds in the ears that received second cochlear implants. Assuming that the auditory pathway beyond the superior olivary complex remained functional, the reduced speech perception abilities associated with the second cochlear implants may have been attributable to the loss of the spiral ganglion and cochlear nucleus cells due to a lack of auditory input since birth.

Effect of Combining Sound Therapy with Pharmacotherapy on the Recovery of Hearing Abilities in the Case of Sudden Sensorineural Hearing Loss: A Prospective Study

INTRODUCTION

This study investigated the effect of sound therapy combined with drug therapy (SDT) on gap detection threshold and speech recognition scores in patients with sudden sensorineural hearing loss (SSNHL).

METHODS

Patients with SSNHL were grouped randomly into SDT and drug therapy (DT) groups. All patients received standard drug treatment and patients in the SDT group additionally received sound stimulation for the affected ears for 6 days. Pure tone audiogram, speech recognition scores at normal and time-compressed rates under quiet and noisy conditions, and the gap detection threshold of the SDT and DT groups before treatment and on day 6 and 30 after treatment were compared.

RESULTS

There were 20 patients in the SDT group and 24 in the DT group. The pure tone thresholds of affected ears were significantly lower in the SDT group on day 6 after treatment than those in the DT group at 125 and 250 Hz. Significantly lower gap detection thresholds and higher speech recognition scores under noisy conditions were observed at the normal and time-compressed rates in the SDT group than those in the DT group on day 6 and 30 after treatment. Significant correlations were observed between the gap thresholds and speech recognition scores in a noisy environment at normal and time-compressed rates on day 6 and 30.

CONCLUSIONS

SDT may improve the recovery of hearing abilities, such as the gap in noise thresholds and speech recognition in noise, in the case of SSNHL.

TRIAL REGISTRATION NUMBER

ChiCTR-IOR-17012262.

Functional Magnetic Resonance Imaging Reveals Early Connectivity Changes in the Auditory and Vestibular Cortices in Idiopathic Sudden Sensorineural Hearing Loss With Vertigo: A Pilot Study

The underlying pathophysiology of idiopathic sudden sensorineural hearing loss (ISSNHL) with vertigo has yet to be identified. The aims of the current study were (1) to elucidate whether there are functional changes of the intrinsic brain activity in the auditory and vestibular cortices of the ISSNHL patients with vertigo using resting-state functional magnetic resonance imaging (rs-fMRI) and (2) whether the connectivity alterations are related to the clinical performance associated with ISSNHL with vertigo. Twelve ISSNHL patients with vertigo, eleven ISSNHL patients without vertigo and eleven healthy subjects were enrolled in this study. Rs-fMRI data of auditory and vestibular cortices was extracted and regional homogeneity (ReHo) and seed-based functional connectivity (FC) were evaluated; the chi-square test, the ANOVA and the Bonferroni multiple comparison tests were performed. Significantly decreased ReHo in the ipsilateral auditory cortex, as well as increased FC between the inferior parietal gyrus and the auditory cortex were found in the ISSNHL with vertigo groups. These findings contribute to a characterization of early plastic changes in ISSNHL patients with vertigo and cultivate new insights for the etiology research.

Conductive Hearing Loss Aggravates Memory Decline in Alzheimer Model Mice

The study of cognitive impairment associated with hearing loss has recently garnered considerable interest. Epidemiological data have demonstrated that hearing loss is a risk factor for cognitive decline as a result of aging. However, no previous study has examined the effect of hearing loss in patients with cognitive problems such as Alzheimer’s disease. Therefore, we investigated the effect of conductive hearing loss in an Alzheimer’s mouse model. Positron emission tomography (PET) and magnetic resonance imaging (MRI) were used to evaluate changes in glucose metabolism and gray matter concentrations in the 5xFAD Alzheimer’s Disease (AD) transgenic mouse model with and without conductive hearing loss (HL). Conductive hearing loss was induced using chronic perforation of the tympanic membrane. Behavioral data from the Y-maze and passive avoidance tests revealed greater memory deficits in the AD with HL (AD-HL) group than in the AD group. Following induction of hearing loss, lower cerebral glucose metabolism in the frontal association cortex was observed in the AD-HL group than in the AD group. Although lower glucose metabolism in the hippocampus and cerebellum was found in the AD-HL group than in the AD group at 3 months, the gray matter concentrations in these regions were not significantly different between the groups. Furthermore, the gray matter concentrations in the simple lobule, cingulate/retrosplenial cortex, substantia nigra, retrosigmoid nucleus, medial geniculate nucleus, and anterior pretectal nucleus at 7 months were significantly lower in the AD-HL group than in the AD group. Taken together, these results indicate that even partial hearing loss can aggravate memory impairment in Alzheimer’s disease.

Inefficient Involvement of Insula in Sensorineural Hearing Loss

The insular cortex plays an important role in multimodal sensory processing, audio-visual integration and emotion; however, little is known about how the insula is affected by auditory deprivation due to sensorineural hearing loss (SNHL). To address this issue, we used structural and functional magnetic resonance imaging to determine if the neural activity within the insula and its interregional functional connectivity (FC) was disrupted by SNHL and if these alterations were correlated clinical measures of emotion and cognition. Thirty-five SNHL subjects and 54 Controls enrolled in our study underwent auditory evaluation, neuropsychological assessments, functional and structure MRI, respectively. Twenty five patients and 20 Controls underwent arterial spin labeling scanning. FC of six insula subdivisions were assessed and the FC results were compared to the neuropsychological tests. Interregional connections were also compared among insula-associated networks, including salience network (SN), default mode network (DMN), and central executive network (CEN). Compared to Controls, SNHL subjects demonstrated hyperperfusion in the insula and significantly decreased FC between some insula subdivisions and other brain regions, including thalamus, putamen, precentral gyrus, postcentral gyrus, mid-cingulate cortex, dorsolateral prefrontal cortex, rolandic operculum. Anxiety, depression and cognitive impairments were correlated with FC values. Abnormal interactions among SN, DMN, and CEN were observed in SNHL group. Our result provides support for the "inefficient high-order control" theory of the insula in which the auditory deprivation caused by SNHL contributes to impaired sensory integration and central deficits in emotional and cognitive processing.

Activation in the auditory pathway of the gerbil studied with 18F-FDG PET: effects of anesthesia

Here, we present results from an ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) study in the Mongolian gerbil, a preferred animal model in auditory research. One major issue in preclinical nuclear imaging, as well as in most of the neurophysiological methods investigating auditory processing, is the need of anesthesia. We compared the usability of two types of anesthesia which are frequently employed in electrophysiology, ketamine/xylazine (KX), and fentanyl/midazolam/medetomidine (FMM), for valid measurements of auditory activation with ¹⁸F-FDG PET. Gerbils were placed in a sound-shielding box and injected with ¹⁸F-FDG. Two acoustic free-field conditions were used: (1) baseline (no stimulation, 25 dB background noise) and (2) 90 dB frequency-modulated tones (FM). After 40 min of ¹⁸F-FDG uptake, a 30 min acquisition was performed using a small animal PET/CT system. Blood glucose levels were measured after the uptake phase before scanning. Standardized uptake value ratios for relevant regions were determined after implementing image and volume of interest templates. Scans demonstrated a significantly higher uptake in the inferior colliculus with FM stimulation compared to baseline in awake subjects (+ 12%; p = 0.02) and with FMM anesthesia (+ 13%; p = 0.0012), but not with KX anesthesia. In non-auditory brain regions, no significant difference was detected. Blood glucose levels were significantly higher under KX compared to FMM anesthesia (17.29 ± 0.42 mmol/l vs. 14.30 ± 1.91 mmol/l; p = 0.024). These results suggest that valid ¹⁸F-FDG PET measurements of auditory activation comparable to electrophysiology can be obtained from gerbils during opioid-based anesthesia due to its limited effects on interfering blood glucose levels.

Early cortical metabolic rearrangement related to clinical data in idiopathic sudden sensorineural hearing loss

Results in studies concerning cortical changes in idiopathic sudden sensorineural hearing loss (ISSNHL) are not homogeneous, in particular due to the different neuroimaging techniques implemented and the diverse stages of ISSNHL studied. Considering the recent advances in state-of-the-art positron emission tomography (PET) cameras, the aim of this study was to gain more insight into the neuroanatomical differences associated with the earliest stages of unilateral ISSNHL and clinical-perceptual performance changes. After an audiological examination including the mean auditory threshold (mean AT), mean speech discrimination score (mean SDS) and Tinnitus Handicap Inventory (THI), 14 right-handed ISSNHL patients underwent brain [¹⁸F]fluorodeoxyglucose (FDG)-PET within 72 h of the onset of symptoms. When compared to an homogeneous group of 35 healthy subjects by means of statistical parametric mapping, a relative increase in FDG uptake was found in the right superior and medial frontal gyrus as well as in the right anterior cingulate cortex in ISSNHL patients. Conversely, the same group showed a significant relative decrease in FDG uptake in the right middle temporal, precentral and postcentral gyrus as well as in the left posterior cingulate cortex, left lingual, superior, middle temporal and middle frontal gyrus and in the left insula. Regression analysis showed a positive correlation between mean THI and glucose consumption in the right anterior cingulate cortex and a positive correlation between mean SDS and glucose consumption in the left precentral gyrus. The relative changes in FDG uptake found in these brain regions and the positive correlation with mean SDS and THI scores in ISSNHL could possibly highlight new aspects of cerebral rearrangement, contributing to further explain changes in those functions that support speech recognition during the sudden impairment of unilateral auditory input.