The impact of mild-to-severe hearing loss on the neural dynamics serving verbal working memory processing in children

Growing together: Dynamic connectivity between developmentally sensitive regions serving verbal working memory in children and adolescents

The neural network serving verbal working memory processes undergoes dramatic changes during the transition from childhood to adolescence, including changes in cortical thickness, activation levels, connectivity and inherent dynamics. Of all these neural properties, maturational changes in dynamic functional connectivity among developmentally sensitive regions within this network are among the least understood. To address this, we examined 75 typically developing youth (age range 6-14 years), who completed a verbal working memory task during magnetoencephalography (MEG). All MEG data were imaged and the phase-locking value was computed as an index of functional connectivity between regions exhibiting significant relationships with chronological age. Our results suggested developmental differences in functional connectivity during specific phases of working memory processing. During encoding, connectivity increased with age between left prefrontal and inferior parietal, with such age-related increases varying by sex between right frontal and left occipitotemporal regions. During the maintenance period, connectivity increased with age between left occipitotemporal and right posterior parietal areas and decreased with age between left frontal and right occipital cortices. These findings suggest that neural oscillations within regions serving working memory processing, as well as functional connectivity among these regions, are modulated by development during the transition from childhood to adolescence. KEY POINTS: With development from childhood to adolescence, verbal working memory processing becomes increasingly left lateralized in the prefrontal, parietal and temporal cortices. Several electrophysiological studies have shown that alpha oscillations within these brain regions become stronger with increasing chronological age during the transition from childhood to adolescence. Although such oscillatory power differences are well established, age-related changes in functional connectivity among these brain regions is far less understood. Here, we report novel findings suggesting that functional connectivity between developmentally sensitive cortical regions supporting verbal working memory scales with age among visual, language and attention-related brain systems. These results help to refine models of functional neural development supporting verbal working memory ability for future application in both basic research and clinical studies of typical and atypical cognitive development.

Distinct age-related alterations in alpha-beta neural oscillatory activity during verbal working memory encoding in children and adolescents

Emerging imaging studies of working memory (WM) have identified significant WM-related oscillatory events that are unique to each phase of working memory (e.g. encoding, maintenance). Although many previous imaging studies have shown age-related changes within the frontoparietal network when performing a WM task, understanding of the age-related changes in the oscillatory dynamics underlying each phase of WM during development and their relationships to other cognitive function is still in its infancy. To this end, we enrolled a group of 74 typically-developing youths aged 7-15 years to perform a letter-based Sternberg WM task during magnetoencephalography. Trial-wise data were transformed into the time-frequency domain, and significant oscillatory responses during the encoding and maintenance phases of the task were independently imaged using beamforming. Our results revealed widespread age-related power differences in alpha-beta oscillatory activity during encoding throughout left frontal, parietal, temporal, occipital and cerebellar regions. By contrast, age-related differences in maintenance-related activity were limited to a small area in the superior temporal gyrus and parieto-occipital regions. Follow-up exploratory factor analysis of age-related encoding alpha-beta activity revealed two distinct factors, and these factors were each found to significantly mediate age-related improvements in both verbal and non-verbal cognitive ability. Additionally, late maintenance alpha activity was related to reaction time on the task. Taken together, our results indicate that the neural dynamics in the alpha and beta bands are uniquely sensitive to age-related changes throughout this developmental period and are related to both task performance and other aspects of cognitive development. KEY POINTS: Understanding of the age-related changes in neural oscillatory dynamics serving verbal working memory function is in its infancy. This study identified the age-related neural alterations during each phase of working memory processing in youths. Developmental differences during working memory processing were primarily isolated to alpha-beta activity during the encoding phase. Alpha-beta activity during encoding significantly mediated age-related improvements in both verbal and non-verbal ability. This study establishes new brain-behaviour relationships linking working memory function to other aspects of cognitive development.

The association between amblyopia and the risks of hearing loss: A propensity matched analysis

INTRODUCTION

Amblyopia occurs due to an imbalance in the visual input between the eyes. This can induce structural changes in the central nervous system and, if left untreated, eventually lead to permanent blindness in the affected eye. As these changes may also impact the auditory system, which closely interacts with the visual system, this study aimed to investigate the risk of hearing loss in patients with amblyopia.

MATERIALS AND METHODS

This study was a retrospective review of the electronic medical records contained in a United States national database of medical records. Patients younger than 18 years old with and without amblyopia were matched and compared to evaluate the relative risk (RR) of having a hearing loss. Stratified analyses were further performed to explore whether the disease laterality and the amblyopia subtype influenced the risks.

RESULTS

Compared to the controls, patients with amblyopia had a higher overall risk of having hearing loss (RR: 1.09, CI: 1.03-1.14), specifically sensorineural hearing loss (SNHL) (RR: 1.24, CI: 1.08-1.42). The stratified analysis further revealed that SNHL was associated with refractive amblyopia (RR: 1.84, CI: 1.50-2.26), but not strabismic amblyopia (RR: 1.23, CI: 1.10-1.38). The laterality of amblyopia did not influence the risk of hearing loss.

CONCLUSIONS

Children with amblyopia have a higher rate of SNHL than children without amblyopia. As vision and hearing are essential in the proper cognitive development, language acquisition, and social and emotional well-being of children, patients with amblyopia may benefit from more frequent audiologic screening.

High-definition transcranial direct current stimulation of the parietal cortices modulates the neural dynamics underlying verbal working memory

Verbal working memory (vWM) is an essential limited-capacity cognitive system that spans the fronto-parietal network and utilizes the subprocesses of encoding, maintenance, and retrieval. With the recent widespread use of noninvasive brain stimulation techniques, multiple recent studies have examined whether such stimulation may enhance cognitive abilities such as vWM, but the findings to date remain unclear in terms of both behavior and critical brain regions. In the current study, we applied high-definition direct current stimulation to the left and right parietal cortices of 39 healthy adults in three separate sessions (left anodal, right anodal, and sham). Following stimulation, participants completed a vWM task during high-density magnetoencephalography (MEG). Significant neural responses at the sensor-level were imaged using a beamformer and whole-brain ANOVAs were used to identify the specific neuromodulatory effects of the stimulation conditions on neural responses serving distinct phases of vWM. We found that right stimulation had a faciliatory effect relative to left stimulation and sham on theta oscillations during encoding in the right inferior frontal, while the opposite pattern was observed for left supramarginal regions. Stimulation also had a faciliatory effect on theta in occipital regions and alpha in temporal regions regardless of the laterality of stimulation. In summary, our data suggest that parietal HD-tDCS both facilitates and interferes with neural responses underlying both the encoding and maintenance phases of vWM. Future studies are warranted to determine whether specific tDCS parameters can be tuned to accentuate the facilitation responses and attenuate the interfering aspects.

Effects of endogenous testosterone on oscillatory activity during verbal working memory in youth

Testosterone levels sharply rise during the transition from childhood to adolescence and these changes are known to be associated with changes in human brain structure. During this same developmental window, there are also robust changes in the neural oscillatory dynamics serving verbal working memory processing. Surprisingly, whereas many studies have investigated the effects of chronological age on the neural oscillations supporting verbal working memory, none have probed the impact of endogenous testosterone levels during this developmental period. Using a sample of 89 youth aged 6-14 years-old, we collected salivary testosterone samples and recorded magnetoencephalography during a modified Sternberg verbal working memory task. Significant oscillatory responses were identified and imaged using a beamforming approach and the resulting maps were subjected to whole-brain ANCOVAs examining the effects of testosterone and sex, controlling for age, during verbal working memory encoding and maintenance. Our primary results indicated robust testosterone-related effects in theta (4-7 Hz) and alpha (8-14 Hz) oscillatory activity, controlling for age. During encoding, females exhibited weaker theta oscillations than males in right cerebellar cortices and stronger alpha oscillations in left temporal cortices. During maintenance, youth with greater testosterone exhibited weaker alpha oscillations in right parahippocampal and cerebellar cortices, as well as regions across the left-lateralized language network. These results extend the existing literature on the development of verbal working memory processing by showing region and sex-specific effects of testosterone, and are the first results to link endogenous testosterone levels to the neural oscillatory activity serving verbal working memory, above and beyond the effects of chronological age.

Hypertension Impacts the Oscillatory Dynamics Serving the Encoding Phase of Verbal Working Memory

BACKGROUND

Chronic hypertension is known to be a major contributor to cognitive decline, with executive function and working memory being among the domains most commonly affected. Despite the growing literature on such dysfunction in patients with hypertension, the underlying neural processes are poorly understood.

METHODS

In this cross-sectional study, we examine these neural processes by having participants with controlled hypertension, uncontrolled hypertension, and healthy controls perform a verbal working memory task during magnetoencephalography. Neural oscillations associated with the encoding and maintenance components of the working memory task were imaged and statistically evaluated among the 3 groups.

RESULTS

Differences related to hypertension emerged during the encoding phase, where the hypertension groups exhibited weaker α-β oscillatory responses compared with controls in the left parietal cortices, whereas such oscillatory activity differed between the 2 hypertension groups in the right prefrontal regions. Importantly, these neural responses in the prefrontal and parietal cortices during encoding were also significantly associated with behavioral performance across all participants.

CONCLUSIONS

Overall, our data suggest that hypertension is associated with neurophysiological abnormalities during working memory encoding, whereas the neural processes serving maintenance seem to be preserved. The right hemispheric neural responses likely reflected compensatory processing, which patients with controlled hypertension may use to achieve verbal working memory function at the level of controls, as opposed to the uncontrolled hypertension group where diminished resources may have limited such additional recruitment.

Better with age: Developmental changes in oscillatory activity during verbal working memory encoding and maintenance

Numerous investigations have characterized the oscillatory dynamics serving working memory in adults, but few have probed its relationship with chronological age in developing youth. We recorded magnetoencephalography during a modified Sternberg verbal working memory task in 82 youth participants aged 6-14 years old. Significant oscillatory responses were identified and imaged using a beamforming approach and the resulting whole-brain maps were probed for developmental effects during the encoding and maintenance phases. Our results indicated robust oscillatory responses in the theta (4-7 Hz) and alpha (8-14 Hz) range, with older participants exhibiting stronger alpha oscillations in left-hemispheric language regions. Older participants also had greater occipital theta power during encoding. Interestingly, there were sex-by-age interaction effects in cerebellar cortices during encoding and in the right superior temporal region during maintenance. These results extend the existing literature on working memory development by showing strong associations between age and oscillatory dynamics across a distributed network. To our knowledge, these findings are the first to link chronological age to alpha and theta oscillatory responses serving working memory encoding and maintenance, both across and between male and female youth; they reveal robust developmental effects in crucial brain regions serving higher order functions.

Comparative Analysis of Intellectual Quotient in Developmental Population with Severe Hearing Loss: Hearing Aids vs. Cochlear Implant Users

The development of language, memory and intellectual functions is linked to normal hearing and correct sounds interpretation. Hearing loss (HL), especially in its severe form, negatively affects the development of these functions. This prospective study aimed at comparing the Intelligent Quotients (IQ) of children with cochlear implants (CI) with the ones of people wearing hearing aids (HA) after one year of hearing rehabilitation. 21 subjects with severe/profound bilateral hearing loss (deafness) were included in this study. Eleven children with congenital profound HL underwent CI and ten children with moderate to severe HL (congenital and acquired) were rehabilitated by HA. Children's IQs were assessed at enrolment (T0) and 12 months after hearing aids/CI use plus speech therapy. Statistical analyses were performed to analyze the data within and between groups. Comparison of IQs showed no statistically significant differences between CI and HA none at T0 and T1. The subtests showed lower scores in verbal comprehension and process speed index in patients treated with HA when compared to CI. This study showed that auditory rehabilitation can support the normal development of cognitive function in children between six and eight years of age. The use of the correct hearing aids based on the patient's hearing thresholds is important to maximize the rehabilitation outcomes. Due to the small sample size, although stratified for age, our results must be considered preliminary and further analyses on larger samples are needed to confirm our data.

Somatosensory gating is related to behavioral and verbal outcomes in children with mild-to-severe hearing loss

Sensory gating is a process by which the brain filters out redundant information to preserve neural resources for behaviorally relevant stimuli. Although studies have shown alterations in auditory and visual processing in children who are hard-of-hearing (CHH) relative to children with normal hearing (CNH), it is unclear whether these alterations extend to the somatosensory domain, and how aberrations in sensory processing affect sensory gating. In this study, CHH and CNH were presented with a paired-pulse median nerve stimulation during magnetoencephalography. Stimulus-related gamma neural activity was imaged and virtual time series from peak somatosensory responses were extracted. We found significant effects of both stimulus and group, as well as a significant group-by-stimulus interaction. CHH showed a larger response to stimulation overall, as well as greater differences in gamma power from the first to the second stimulus. However, when looking at the ratio rather than the absolute difference in power, CHH showed comparable gating to CNH. In addition, smaller gating ratios were correlated with better classroom behavior and verbal ability in CHH, but not CNH. Taken together, these data underscore the importance of considering how CHH experience their multisensory environment when interpreting outcomes and designing interventions.

Amount of Hearing Aid Use Impacts Neural Oscillatory Dynamics Underlying Verbal Working Memory Processing for Children With Hearing Loss

OBJECTIVES

Children with hearing loss (CHL) may exhibit spoken language delays and may also experience deficits in other cognitive domains including working memory. Consistent hearing aid use (i.e., more than 10 hours per day) ameliorates these language delays; however, the impact of hearing aid intervention on the neural dynamics serving working memory remains unknown. The objective of this study was to examine the association between the amount of hearing aid use and neural oscillatory activity during verbal working memory processing in children with mild-to-severe hearing loss.

DESIGN

Twenty-three CHL between 8 and 15 years-old performed a letter-based Sternberg working memory task during magnetoencephalography (MEG). Guardians also completed a questionnaire describing the participants' daily hearing aid use. Each participant's MEG data was coregistered to their structural MRI, epoched, and transformed into the time-frequency domain using complex demodulation. Significant oscillatory responses corresponding to working memory encoding and maintenance were independently imaged using beamforming. Finally, these whole-brain source images were correlated with the total number of hours of weekly hearing aid use, controlling for degree of hearing loss.

RESULTS

During the encoding period, hearing aid use negatively correlated with alpha-beta oscillatory activity in the bilateral occipital cortices and right precentral gyrus. In the occipital cortices, this relationship suggested that with greater hearing aid use, there was a larger suppression of occipital activity (i.e., more negative relative to baseline). In the precentral gyrus, greater hearing aid use was related to less synchronous activity (i.e., less positive relative to baseline). During the maintenance period, hearing aid use significantly correlated with alpha activity in the right prefrontal cortex, such that with greater hearing aid use, there was less right prefrontal maintenance-related activity (i.e., less positive relative to baseline).

CONCLUSIONS

This study is the first to investigate the impact of hearing aid use on the neural dynamics that underlie working memory function. These data show robust relationships between the amount of hearing aid use and phase-specific neural patterns during working memory encoding and maintenance after controlling for degree of hearing loss. Furthermore, our data demonstrate that wearing hearing aids for more than ~8.5 hours/day may serve to normalize these neural patterns. This study also demonstrates the potential for neuroimaging to help determine the locus of variability in outcomes in CHL.

Auditory experience modulates frontoparietal theta activity serving fluid intelligence

Children who are hard of hearing are at risk for developmental language and academic delays compared with children with normal hearing. Some work suggests that high-order cognitive function, including fluid intelligence, may relate to language and academic outcomes in children with hearing loss, but findings in these studies have been mixed and to date, there have been no studies of the whole-brain neural dynamics serving fluid intelligence in the context of hearing loss. To this end, this study sought to identify the impact of hearing loss and subsequent hearing aid use on the neural dynamics serving abstract reasoning in children who are hard of hearing relative to children with normal hearing using magnetoencephalography. We found significant elevations in occipital and parietal theta activity during early stimulus evaluation in children who are hard of hearing relative to normal-hearing peers. In addition, we found that greater hearing aid use was significantly related to reduced activity throughout the fronto-parietal network. Notably, there were no differences in alpha dynamics between groups during later-stage processing nor did alpha activity correlate with hearing aid use. These cross-sectional data suggest that differences in auditory experience lead to widespread alterations in the neural dynamics serving initial stimulus processing in fluid intelligence in children.

Auditory Sensory Gating in Children With Cochlear Implants: A P50-N100-P200 Study

Background: While a cochlear implant (CI) can restore access to audibility in deaf children, implanted children may still have difficulty in concentrating. Previous studies have revealed a close relationship between sensory gating and attention. However, whether CI children have deficient auditory sensory gating remains unclear.

Methods: To address this issue, we measured the event-related potentials (ERPs), including P50, N100, and P200, evoked by paired tone bursts (S1 and S2) in CI children and normal-hearing (NH) controls. Suppressed amplitudes for S2 compared with S1 in these three ERPs reflected sensory gating during early and later phases, respectively. A Swanson, Nolan, and Pelham IV (SNAP-IV) scale was performed to assess the attentional performance.

Results: Significant amplitude differences between S1 and S2 in N100 and P200 were observed in both NH and CI children, indicating the presence of sensory gating in the two groups. However, the P50 suppression was only found in NH children and not in CI children. Furthermore, the duration of deafness was significantly positively correlated with the score of inattention in CI children.

Conclusion: Auditory sensory gating can develop but is deficient during the early phase in CI children. Long-term auditory deprivation has a negative effect on sensory gating and attentional performance.

Effects of long-term unilateral cochlear implant use on large-scale network synchronization in adolescents

Unilateral cochlear implantation (CI) limits deafness-related changes in the auditory pathways but promotes abnormal cortical preference for the stimulated ear and leaves the opposite ear with little protection from auditory deprivation. In the present study, time-frequency analyses of event-related potentials elicited from stimuli presented to each ear were used to determine effects of unilateral CI use on cortical synchrony. CI-elicited activity in 34 adolescents (15.4±1.9 years of age) who had listened with unilateral CIs for most of their lives prior to bilateral implantation were compared to responses elicited by a 500Hz tone-burst in normal hearing peers. Phase-locking values between 4 and 60Hz were calculated for 171 pairs of 19-cephalic recording electrodes. Ear specific results were found in the normal hearing group: higher synchronization in low frequency bands (theta and alpha) from left ear stimulation in the right hemisphere and more high frequency activity (gamma band) from right ear stimulation in the left hemisphere. In the CI group, increased phase synchronization in the theta and beta frequencies with bursts of gamma activity were elicited by the experienced-right CI between frontal, temporal and parietal cortical regions in both hemispheres, consistent with increased recruitment of cortical areas involved in attention and higher-order processes, potentially to support unilateral listening. By contrast, activity was globally desynchronized in response to initial stimulation of the naïve-left ear, suggesting decoupling of these pathways from the cortical hearing network. These data reveal asymmetric auditory development promoted by unilateral CI use, resulting in an abnormally mature neural network.