Improving rehabilitation of deaf patients by advanced imaging before cochlear implantation.

INTRODUCTION: Cochlear implants have advanced the management of severe to profound deafness. However, there is a strong disparity in hearing performance after implantation from one patient to another. Moreover, there are several advanced kinds of imaging assessment before cochlear implantation. Microstructural white fiber degeneration can be studied with Diffusion weighted MRI (DWI) or tractography of the central auditory pathways. Functional MRI (fMRI) allows us to evaluate brain function, and CT or MRI segmentation to better detect inner ear anomalies. OBJECTIVE: This literature review aims to evaluate how helpful pre-implantation anatomic imaging can be to predict hearing rehabilitation outcomes in deaf patients. These techniques include DWI and fMRI of the central auditory pathways, and automated labyrinth segmentation by CT scan, cone beam CT and MRI. DESIGN: This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies were selected by searching in PubMed and by checking the reference lists of relevant articles. Inclusion criteria were adults over 18, with unilateral or bilateral hearing loss, who had DWI acquisition or fMRI or CT/ Cone Beam CT/ MRI image segmentation. RESULTS: After reviewing 172 articles, we finally included 51. Studies on DWI showed changes in the central auditory pathways affecting the white matter, extending to the primary and non-primary auditory cortices, even in sudden and mild hearing impairment. Hearing loss patients show a reorganization of brain activity in various areas, such as the auditory and visual cortices, as well as regions involved in language and emotions, according to fMRI studies. Deep Learning's automatic segmentation produces the best CT segmentation in just a few seconds. MRI segmentation is mainly used to evaluate fluid space of the inner ear and determine the presence of an endolymphatic hydrops. CONCLUSION: Before cochlear implantation, a DWI with tractography can evaluate the central auditory pathways up to the primary and non-primary auditory cortices. This data is then used to generate predictions on the auditory rehabilitation of patients. A CT segmentation with systematic 3D reconstruction allow a better evaluation of cochlear malformations and predictable difficulties during surgery.

Neuroplastic changes in functional wiring in sensory cortices of the congenitally deaf: A network analysis.

Congenital sensory deprivation induces significant changes in the structural and functional organisation of the brain. These are well-characterised by cross-modal plasticity, in which deprived cortical areas are recruited to process information from non-affected sensory modalities, as well as by other neuroplastic alterations within regions dedicated to the remaining senses. Here, we analysed visual and auditory networks of congenitally deaf and hearing individuals during different visual tasks to assess changes in network community structure and connectivity patterns due to congenital deafness. In the hearing group, the nodes are clearly divided into three communities (visual, auditory and subcortical), whereas in the deaf group a fourth community consisting mainly of bilateral superior temporal sulcus and temporo-insular regions is present. Perhaps more importantly, the right lateral geniculate body, as well as bilateral thalamus and pulvinar joined the auditory community of the deaf. Moreover, there is stronger connectivity between bilateral thalamic and pulvinar and auditory areas in the deaf group, when compared to the hearing group. No differences were found in the number of connections of these nodes to visual areas. Our findings reveal substantial neuroplastic changes occurring within the auditory and visual networks caused by deafness, emphasising the dynamic nature of the sensory systems in response to congenital deafness. Specifically, these results indicate that in the deaf but not the hearing group, subcortical thalamic nuclei are highly connected to auditory areas during processing of visual information, suggesting that these relay areas may be responsible for rerouting visual information to the auditory cortex under congenital deafness.

Social perception in deaf individuals: A meta-analysis of neuroimaging studies.

Deaf individuals may report difficulties in social interactions. However, whether these difficulties depend on deafness affecting social brain circuits is controversial. Here, we report the first meta-analysis comparing brain activations of hearing and (prelingually) deaf individuals during social perception. Our findings showed that deafness does not impact on the functional mechanisms supporting social perception. Indeed, both deaf and hearing control participants recruited regions of the action observation network during performance of different social tasks employing visual stimuli, and including biological motion perception, face identification, action observation, viewing, identification and memory for signs and lip reading. Moreover, we found increased recruitment of the superior-middle temporal cortex in deaf individuals compared with hearing participants, suggesting a preserved and augmented function during social communication based on signs and lip movements. Overall, our meta-analysis suggests that social difficulties experienced by deaf individuals are unlikely to be associated with brain alterations but may rather depend on non-supportive environments.

Diffusion tensor imaging and auditory tractography to evaluate cochlear implant candidacy: a pilot study.

BACKGROUND: Conventional radiological evaluation does not evaluate the functional status of the auditory pathway in patients scheduled for cochlear implantation (CI). OBJECTIVES: Determine the value of diffusion tensor imaging [DTI] in the preoperative evaluation of some patients scheduled for CI. MATERIAL AND METHODS: Patients with profound SNHL and inner ear and/or cochlear nerve anomalies or long standing SNHL were selected. They underwent conventional MRI images of the brain in three orthogonal planes, MR arterial spin labelling (ASL), perfusion, and DTI auditory tractography to determine functional status of the auditory pathways. RESULTS: Ten patients were included. Seven with bilateral SNHL, one with fluctuating hearing loss and one with long standing single sided deafness. In 8 patients the auditory pathway could be traced and functional maps could determine the side of possible better function. In the patient with progressive hearing loss DTI revealed major central pathway problems and CI was discouraged. In the patient with SSD, DTI revealed a robust intact pathway and CI was advised. CONCLUSIONS: DTI and auditory tractography can help in outlining the functional integrity of the 33auditory pathway and assist in decision making before CI.

Arithmetic in the signing brain: Differences and similarities in arithmetic processing between deaf signers and hearing non-signers.

Deaf signers and hearing non-signers have previously been shown to recruit partially different brain regions during simple arithmetic. In light of the triple code model, the differences were interpreted as relating to stronger recruitment of the verbal system of numerical processing, that is, left angular and inferior frontal gyrus, in hearing non-signers, and of the quantity system of numerical processing, that is, right horizontal intraparietal sulcus, for deaf signers. The main aim of the present study was to better understand similarities and differences in the neural correlates supporting arithmetic in deaf compared to hearing individuals. Twenty-nine adult deaf signers and 29 hearing non-signers were enrolled in an functional magnetic resonance imaging study of simple and difficult subtraction and multiplication. Brain imaging data were analyzed using whole-brain analysis, region of interest analysis, and functional connectivity analysis. Although the groups were matched on age, gender, and nonverbal intelligence, the deaf group performed generally poorer than the hearing group in arithmetic. Nevertheless, we found generally similar networks to be involved for both groups, the only exception being the involvement of the left inferior frontal gyrus. This region was activated significantly stronger for the hearing compared to the deaf group but showed stronger functional connectivity with the left superior temporal gyrus in the deaf, compared to the hearing, group. These results lend no support to increased recruitment of the quantity system in deaf signers. Perhaps the reason for performance differences is to be found in other brain regions not included in the original triple code model.

The gradient in gray matter thickness across auditory cortex and differential cortical thickness changes following perinatal deafness.

In the absence of hearing during development, the brain adapts and repurposes what was destined to become auditory cortex. As cortical thickness is commonly used as a proxy to identify cortical regions that have undergone plastic changes, the purpose of this investigation was to compare cortical thickness patterns between hearing and deaf cats. In this study, normal hearing (n = 29) and deaf (n = 26) cats were scanned to examine cortical thickness in hearing controls, as well as differential changes in thickness as a consequence of deafness. In hearing cats, a gradient in cortical thickness was identified across auditory cortex in which it is thinner in more dorsal regions and thicker in more ventral regions. Compared with hearing controls, differential thickening and thinning was observed in specific regions of deaf auditory cortex. More dorsal regions were found to be bilaterally thicker in the deaf group, while more ventral regions in the left hemisphere were thinner. The location and nature of these changes creates a gradient along the dorsoventral axis, wherein dorsal auditory cortical fields are thicker, whereas more ventral fields are thinner in deaf animals compared with hearing controls.

Cerebellar vermis hypoplasia and bilateral basal ganglia calcification in maternally inherited diabetes and deafness.

Maternally inherited diabetes and deafness (MIDD) is a rare diabetic syndrome mainly caused by a point mutation in the mitochondrial DNA. It affects up to 1% of patients with diabetes but is often unrecognized by physicians. We report a case of MIDD in a 29-year-old man with coexisting imaging of cerebellar vermis hypoplasia and bilateral basal ganglia calcification.

Brain MRI findings of prelingually deaf children and cochlear implant outcome: Preliminary results.

OBJECTIVE: To estimate the incidence of brain abnormalities in a cohort of prelingually deaf children and whether these abnormalities can impact the hearing outcomes of patients eligible for cochlear implantation (CI). METHODS: We performed a retrospective review of consecutive medical charts of prelingually deaf children under 12 years of age who underwent brain magnetic resonance imaging (MRI) during their preoperative workup for CI surgery. We used the category of auditory performance (CAP) test and the speech intelligibility rating (SIR) test to assess the hearing and speech performance of the children, respectively. RESULTS: The MRIs of 285 patients, 174 boys and 111 girls with a mean age of 36.4 (±16) months, were evaluated for this study. We identified 31 patients with abnormal findings (10.88%): (17/31) (54.8%) had MRI brain abnormalities, (9/31) (29%) had inner ear anomalies, and (5/31) (16.1%) had both inner ear and brain abnormalities. The most frequent inner ear anomaly was an enlarged vestibular aqueduct, while white matter lesions were the most common brain abnormality. The CAP and SIR mean score of patients with inner ear anomalies was slightly, but not significantly, higher than those of patients with brain abnormalities. CONCLUSION: CAP and SIR scores were not significantly different in children with brain abnormalities than inner ear anomalies. These patients can still benefit from CI to improve their overall hearing and speech performance.

Functional connectivity alteration of the deprived auditory regions with cognitive networks in deaf and inattentive adolescents.

Adolescents with early profound deafness may present with distractibility and inattentiveness. The brain mechanisms underlying these attention impairments remain unclear. We performed resting-state functional magnetic resonance imaging to investigate the functional connectivity of the superior temporal and transverse temporal gyri in 25 inattentive adolescents with bilateral prelingual profound deafness, and compared the results with those of 27 age-matched normal controls. Pearson and Spearman's rho correlation analyses were used to investigate the correlations of altered functional connectivity with the clinical parameters, including the duration of hearing loss sign language, and hearing aid usage. Compared with normal controls, prelingual profound deafness demonstrated mainly decreased resting-state functional connectivity between the deprived auditory regions and several other brain functional networks, including the attention control, language comprehension, default-mode, and sensorimotor networks. Moreover, we also found enhanced resting-state functional connectivity between the deprived auditory cortex and salience network. These results indicate a negative impact of early hearing loss on the attentional and other high cognitive networks, and the use of sign language and hearing aids normalized the participants' connectivity between the primary auditory cortex and attention networks, which is crucial for the early intervention and clinical care of deaf adolescents.

De Novo ACTG1 Variant Expands the Phenotype and Genotype of Partial Deafness and Baraitser-Winter Syndrome.

Actin molecules are fundamental for embryonic structural and functional differentiation; γ-actin is specifically required for the maintenance and function of cytoskeletal structures in the ear, resulting in hearing. Baraitser-Winter Syndrome (B-WS, OMIM #243310, #614583) is a rare, multiple-anomaly genetic disorder caused by mutations in either cytoplasmically expressed actin gene, ACTB (ß-actin) or ACTG1 (γ-actin). The resulting actinopathies cause characteristic cerebrofrontofacial and developmental traits, including progressive sensorineural deafness. Both ACTG1-related non-syndromic A20/A26 deafness and B-WS diagnoses are characterized by hypervariable penetrance in phenotype. Here, we identify a 28th patient worldwide carrying a mutated γ-actin ACTG1 allele, with mildly manifested cerebrofrontofacial B-WS traits, hypervariable penetrance of developmental traits and sensorineural hearing loss. This patient also displays brachycephaly and a complete absence of speech faculty, previously unreported for ACTG1-related B-WS or DFNA20/26 deafness, representing phenotypic expansion. The patient's exome sequence analyses (ES) confirms a de novo ACTG1 variant previously unlinked to the pathology. Additional microarray analysis uncover no further mutational basis for dual molecular diagnosis in our patient. We conclude that γ-actin c.542C > T, p.Ala181Val is a dominant pathogenic variant, associated with mildly manifested facial and cerebral traits typical of B-WS, hypervariable penetrance of developmental traits and sensorineural deafness. We further posit and present argument and evidence suggesting ACTG1-related non-syndromic DFNA20/A26 deafness is a manifestation of undiagnosed ACTG1-related B-WS.

Reorganization of large-scale brain networks in deaf signing adults: The role of auditory cortex in functional reorganization following deafness.

If the brain is deprived of input from one or more senses during development, functional and structural reorganization of the deprived regions takes place. However, little is known about how sensory deprivation affects large-scale brain networks. In the present study, we use data-driven independent component analysis (ICA) to characterize large-scale brain networks in 15 deaf early signers and 24 hearing non-signers based on resting-state functional MRI data. We found differences between the groups in independent components representing the left lateralized control network, the default network, the ventral somatomotor network, and the attention network. In addition, we showed stronger functional connectivity for deaf compared to hearing individuals from the middle and superior temporal cortices to the cingulate cortex, insular cortex, cuneus and precuneus, supramarginal gyrus, supplementary motor area, and cerebellum crus 1, and stronger connectivity for hearing non-signers to hippocampus, middle and superior frontal gyri, pre- and postcentral gyri, and cerebellum crus 8. These results show that deafness induces large-scale network reorganization, with the middle/superior temporal cortex as a central node of plasticity. Cross-modal reorganization may be associated with behavioral adaptations to the environment, including superior ability in some visual functions such as visual working memory and visual attention, in deaf signers.

X-linked deafness/incomplete partition type 3: Radiological evaluation of temporal bone and intracranial findings.

PURPOSE: X-linked deafness (XLD) is a rare disease, characterized by typical cochlear incomplete partition type 3 anomaly (IP-III). Accompanying hypothalamic anomalies were also recently described. The purpose of this study was to document the temporal bone and intracranial imaging findings in a series of patients with XLD with a review of the literature, to better understand this anomaly. METHODS: The CT and MRI studied of 13 XLD patients were retrospectively evaluated. All structures of the otic capsule (OC) were subjectively and retrospectively assessed. The OC thickness and the size of the cochlea were measured and compared to the age-matched control group. Intracranial structures were also evaluated with specific attention to the hypothalamic region. RESULTS: All cases had bilateral IP-III anomaly, bulbous internal auditory canals (IACs), absent bony modiolus with preserved interscalar septa, intact cochleovestibular, and facial nerves. OC thickness was decreased in all cases compared to the control group (p<0.001). In XLD patients, the cochlea had decreased transverse dimension and increased height compared to the control group (p< 0.001). Five patients (38.4%) had bilateral cystic structures adjacent to the vestibule and/or semicircular canals (SCCs). Hypothalamus was thickened or had a lobular appearance in all cases (subtle in one). Additionally, hamartoma-like appearance of the hypothalamus was present in half. CONCLUSION: XLD is a rare inner ear anomaly that is frequently associated with hypothalamic malformations. The OC thickness of IP-III patients appears to be decreased with accompanying decreased transverse dimension of the cochlea which could have implications in electrode selection during cochlear implantation. Cystic /diverticular lesions surrounding the vestibule and semicircular canals are also frequently seen but a rarely reported finding.

Alteration of brain resting-state networks and functional connectivity in prelingual deafness.

BACKGROUND AND PURPOSE: Early hearing loss causes several changes in the brain structure and function at multiple levels; these changes can be observed through neuroimaging. These changes are directly associated with sensory loss (hearing) and the acquisition of alternative communication strategies. Such plasticity changes in the brain might establish a different connectivity pattern with resting-state networks (RSNs) and other brain regions. We performed resting-state functional magnetic resonance imaging (rsfMRI) to evaluate these intrinsic modifications. METHODS: We used two methods to characterize the functional connectivity (FC) of RSN components in 20 prelingual deaf adults and 20 demographic-matched hearing adults. rsfMRI data were analyzed using independent component analysis (ICA) and region-of-interest seed-to-voxel correlation analysis. RESULTS: In ICA, we identified altered FC of RSNs in the deaf group. RSNs with altered FC were observed in higher visual, auditory, default mode, salience, and sensorimotor networks. The findings of seed-to-voxel correlation analysis suggested increased temporal coherence with other neural networks in the deaf group compared with the hearing control group. CONCLUSION: These findings suggest a highly diverse resting-state connectivity pattern in prelingual deaf adults resulting from compensatory cross-modal plasticity that includes both auditory and nonauditory regions.

Identification of Novel Compound Heterozygous MYO15A Mutations in Two Chinese Families with Autosomal Recessive Nonsyndromic Hearing Loss.

Congenital deafness is one of the most common causes of disability in humans, and more than half of cases are caused by genetic factors. Mutations of the MYO15A gene are the third most common cause of hereditary hearing loss. Using next-generation sequencing combined with auditory tests, two novel compound heterozygous variants c.2802_2812del/c.5681T>C and c.5681T>C/c.6340G>A in the MYO15A gene were identified in probands from two irrelevant Chinese families. Auditory phenotypes of the probands are consistent with the previously reported for recessive variants in the MYO15A gene. The two novel variants, c.2802_2812del and c.5681T>C, were identified as deleterious mutations by bioinformatics analysis. Our findings extend the MYO15A gene mutation spectrum and provide more information for rapid and precise molecular diagnosis of congenital deafness.

Functional and structural brain connectivity in congenital deafness.

Several studies have been carried out to verify neural plasticity and the language process in deaf individuals. However, further investigations regarding the intrinsic brain organization on functional and structural neural networks derived from congenital deafness are still an open question. The objective of this study was to investigate the main differences in brain organization manifested in congenitally deaf individuals, concerning the resting-state functional patterns, and white matter structuring. Functional and diffusion magnetic resonance imaging modalities were acquired from 18 congenitally deaf individuals and 18 age-sex-matched hearing controls. Compared to the hearing group, the deaf individuals presented higher functional connectivity among the posterior cingulate cortex node of the default mode network with visual and motor networks, lower functional connectivity between salience networks, language networks, and prominence of functional connectivity changes in the right hemisphere, mostly in the frontoparietal and temporal lobes. In terms of structural connectivity, we found changes mainly in the occipital and parietal lobes, involving both classical sign language support regions as well as concentrated networks for focus activity, attention, and cognitive filtering. Our findings demonstrated that the congenital deaf individuals who learned sign language developed significant brain functional and structural reorganization, which provides prominent support for large-scale brain networks associated with attention decision-making, environmental monitoring based on the movement of objects, and on the motor and visual controls.

Working Memory for Signs with Poor Visual Resolution: fMRI Evidence of Reorganization of Auditory Cortex in Deaf Signers.

Stimulus degradation adds to working memory load during speech processing. We investigated whether this applies to sign processing and, if so, whether the mechanism implicates secondary auditory cortex. We conducted an fMRI experiment where 16 deaf early signers (DES) and 22 hearing non-signers performed a sign-based n-back task with three load levels and stimuli presented at high and low resolution. We found decreased behavioral performance with increasing load and decreasing visual resolution, but the neurobiological mechanisms involved differed between the two manipulations and did so for both groups. Importantly, while the load manipulation was, as predicted, accompanied by activation in the frontoparietal working memory network, the resolution manipulation resulted in temporal and occipital activation. Furthermore, we found evidence of cross-modal reorganization in the secondary auditory cortex: DES had stronger activation and stronger connectivity between this and several other regions. We conclude that load and stimulus resolution have different neural underpinnings in the visual-verbal domain, which has consequences for current working memory models, and that for DES the secondary auditory cortex is involved in the binding of representations when task demands are low.

Visual motion processing recruits regions selective for auditory motion in early deaf individuals.

In early deaf individuals, the auditory deprived temporal brain regions become engaged in visual processing. In our study we tested further the hypothesis that intrinsic functional specialization guides the expression of cross-modal responses in the deprived auditory cortex. We used functional MRI to characterize the brain response to horizontal, radial and stochastic visual motion in early deaf and hearing individuals matched for the use of oral or sign language. Visual motion showed enhanced response in the 'deaf' mid-lateral planum temporale, a region selective to auditory motion as demonstrated by a separate auditory motion localizer in hearing people. Moreover, multivariate pattern analysis revealed that this reorganized temporal region showed enhanced decoding of motion categories in the deaf group, while visual motion-selective region hMT+/V5 showed reduced decoding when compared to hearing people. Dynamic Causal Modelling revealed that the 'deaf' motion-selective temporal region shows a specific increase of its functional interactions with hMT+/V5 and is now part of a large-scale visual motion selective network. In addition, we observed preferential responses to radial, compared to horizontal, visual motion in the 'deaf' right superior temporal cortex region that also show preferential response to approaching/receding sounds in the hearing brain. Overall, our results suggest that the early experience of auditory deprivation interacts with intrinsic constraints and triggers a large-scale reallocation of computational load between auditory and visual brain regions that typically support the multisensory processing of motion information.

High-frequency Cochlear Nerve Deficit Region: Relationship With Deaf Duration and Cochlear Implantation Performance in Postlingual Deaf Adults.

OBJECTIVE: To analyze the changes of cochlear nerve diameter and the presence of a cochlear nerve deficit at a high-frequency region and investigate their effects on cochlear implant (CI) performance in postlingual deaf adults. STUDY DESIGN: Retrospective. SETTING: Tertiary care academic center. PATIENTS: Eighty-three postlingual deaf adults with no labyrinthine anomalies or cognitive deficits who received a CI with perimodiolar electrodes from a single manufacturer. MAIN OUTCOMES AND MEASURES: We evaluated the changes of cochlear nerve diameter and the presence of a "tail sign," defined as identifiable nerve fibers originating from the far basal turn of the cochlea, which represents the presence of cochlear nerve at a high-frequency region in magnetic resonance imaging, on monosyllabic word recognition scores. RESULTS: The cochlear nerve diameter showed a positive correlation with word recognition scores (maximum diameter, R2 = 0.26, p < 0.01; minimum diameter, R2 = 0.26, p < 0.01), but a negative correlation with deaf duration. Recipients with a positive tail sign performed better (73 ±â€Š19%) than those without (45 ±â€Š24%, p < 0.01). A positive tail sign was more commonly found in good performers (52 of 62, 84%) than in poor performers (5 of 21, 24%, p < 0.01). CONCLUSIONS: Favorable outcomes could be anticipated in postlingual deaf adults with a large cochlear nerve diameter and positive tail sign. A presence of cochlear nerve at a high-frequency region may be an imaging marker for predicting good CI performance.