Auditory Gating in Hearing Loss

Cortical sensory gating and reactions to dynamic speech-in-noise in older normal-hearing and hearing-impaired adults

OBJECTIVE

To examine whether cortical sensory gating predicts how older adults with and without hearing loss perform the Tracking of Noise Tolerance (TNT) test.

DESIGN

Single-blind mixed design. TNT performance was defined by average tolerated noise relative to speech levels (TNTAve) and by an average range of noise levels over a two-minute trial (excursion). Sensory gating of P1-N1-P2 components was measured using pairs of 1 kHz tone pips.

STUDY SAMPLE

Twenty-three normal-hearing (NH) and 16 hearing-impaired (HI) older adults with a moderate-to-severe degree of sensorineural hearing loss.

RESULTS

NH listeners tolerated significantly more noise than HI listeners, but the two groups did not differ in their excursion. Both NH and HI listeners exhibited significant gating of P1 amplitudes and N1P2 peak-to-peak amplitudes with no difference in gating magnitudes between listener groups. Sensory gating magnitudes of P1 and N1P2 did not predict TNTAve scores, but N1P2 gating negatively predicted excursion after accounting for listener age and hearing thresholds.

CONCLUSIONS

Listeners' reactivity to a roving noise (excursion), but not their average noise tolerance (TNTAve), was predicted by sensory gating at N1P2 generators. These results suggest that temporal aspects of speech-in-noise processing may be affected by declines in the central inhibition of older adults.

Sensory Inhibition and Tinnitus: Measurement of Auditory Gating

Tinnitus is the perception of sound without the presence of an external stimulus. The mechanisms associated with tinnitus are not entirely known, making diagnosis and treatment challenging. Although tinnitus mechanisms are not entirely known, there is evidence supporting an association between tinnitus with cochlear damage, reduced inhibition, and atypical cortical function. These mechanisms have been studied in animal models and people with tinnitus using a variety of different approaches. One approach that is a possible indicator of tinnitus in humans is sensory or auditory gating, which is a measure of inhibition. The goals of this article are to (1) review the mechanistic evidence associating tinnitus with cochlear damage and reduced inhibition, (2) discuss evidence of inhibitory impairments in people with tinnitus represented by auditory gating, and (3) address potential future directions to improve our ability to evaluate auditory gating mechanisms in people with tinnitus.

Auditory Sensory Gating: Effects of Noise

Cortical auditory evoked potentials (CAEPs) indicate that noise degrades auditory neural encoding, causing decreased peak amplitude and increased peak latency. Different types of noise affect CAEP responses, with greater informational masking causing additional degradation. In noisy conditions, attention can improve target signals' neural encoding, reflected by an increased CAEP amplitude, which may be facilitated through various inhibitory mechanisms at both pre-attentive and attentive levels. While previous research has mainly focused on inhibition effects during attentive auditory processing in noise, the impact of noise on the neural response during the pre-attentive phase remains unclear. Therefore, this preliminary study aimed to assess the auditory gating response, reflective of the sensory inhibitory stage, to repeated vowel pairs presented in background noise. CAEPs were recorded via high-density EEG in fifteen normal-hearing adults in quiet and noise conditions with low and high informational masking. The difference between the average CAEP peak amplitude evoked by each vowel in the pair was compared across conditions. Scalp maps were generated to observe general cortical inhibitory networks in each condition. Significant gating occurred in quiet, while noise conditions resulted in a significantly decreased gating response. The gating function was significantly degraded in noise with less informational masking content, coinciding with a reduced activation of inhibitory gating networks. These findings illustrate the adverse effect of noise on pre-attentive inhibition related to speech perception.

Cortical Auditory Evoked Potential Indices of Impaired Sensory Gating in People With Chronic Tinnitus

OBJECTIVES

The primary aim of this study was to evaluate whether there is cortical auditory evoked potential (CAEP) evidence of impaired sensory gating in individuals with tinnitus. On the basis of the proposed mechanism of tinnitus generation, including a thalamocortical inhibitory deficit, it was hypothesized that individuals with tinnitus would lack the normal inhibitory effect on the second CAEP response in a paired-click sensory gating paradigm, resulting in larger sensory gating ratios in individuals with tinnitus relative to age-, sex-, and hearing-matched controls. Further, this study assessed the relative predictive influence of tinnitus presence versus other related individual characteristics (hearing loss, age, noise exposure history, and speech perception in noise) on sensory gating.

DESIGN

A paired-click CAEP paradigm was used to measure sensory gating outcomes in an independent group's experimental design. Adults who perceived chronic unilateral or bilateral tinnitus were matched with control group counterparts without tinnitus by age, hearing, and sex (n = 18; 10 females, eight males in each group). Amplitude, area, and latency sensory gating ratios were determined for measured P1, N1, and P2 responses evoked by the first and second click in the paradigm and compared between groups by independent t tests. The relative influence of tinnitus (presence/absence), age (in years), noise exposure history (subjective self-report), hearing loss (pure-tone audiometric thresholds), and speech perception in noise (signal to noise ratio-50) on sensory gating was determined based on the proportional reduction in error associated with each variable using multiple regression.

RESULTS

A significantly larger was identified in the tinnitus group relative to the control group, consistent with the hypothesis of poorer sensory gating and poorer thalamocortical inhibition in individuals with chronic tinnitus. On the basis of the proportional reduction in error, the influence of tinnitus presence better predicted compared with other related individual characteristics (age, noise exposure history, hearing loss, and speech perception in noise).

CONCLUSIONS

Results consistent with poorer sensory gating, including a larger , were found for the tinnitus group compared with the controls. This finding supported a thalamocortical inhibitory deficit in the tinnitus group and suggests that individuals with tinnitus may have poorer sensory gating. However, the tinnitus group did differ from controls in meaningful ways including having worse pure-tone thresholds in the extended high-frequency region, lower high-frequency distortion product otoacoustic emissions, and poorer speech perception in noise. Although tinnitus best predicted sensory gating outcomes, the specific effects of tinnitus presence versus absence and other individual characteristics on sensory gating cannot be completely separated.

Sensory Gating in the Auditory System: Classical and Novel Stimulus Paradigms

PURPOSE

Sensory gating is a phenomenon where the cortical response to the second stimulus in a pair of identical stimuli is inhibited. It is most often assessed in a conditioning-testing paradigm. Both active and passive neuronal mechanisms have been implicated in sensory gating. The present study aimed to assess if sensory gating is caused by an active neural mechanism associated with stimulus redundancy.

METHOD

The study was carried out on 20 young neurotypical adults. We assessed the gating phenomenon using identical and nonidentical stimuli pairs presented in an electrophysiological conditioning-testing paradigm. We hypothesized that the novel stimulus in the nonidentical stimulus pair would not exhibit the sensory gating effects (reduction in the amplitude of cortical potentials to the second stimuli in the pair), owing to stimulus novelty.

RESULTS

Contrary to our expectations, the response analyses of the cortical auditory evoked potentials revealed that adults gated repetitive and novel stimuli similarly.

CONCLUSIONS

The findings are discussed in relation to the significance of methodological factors in evaluating sensory gating. We believe that additional research using oddball presentation of novel stimuli along with appropriate analysis methods is necessary before drawing any conclusions on the mechanisms underlying sensory gating.

Sensory Gating Networks in Normal-Hearing Adults With Minimal Tinnitus

PURPOSE

The goal of this study was to observe sensory gating-related networks underlying cortical auditory evoked potential (CAEP) peak components in individuals with and without minimal tinnitus, as measured using the Tinnitus Handicap Inventory (THI). This analysis was performed on previously published sensory gating responses in normal-hearing adults with and without minimal tinnitus.

METHOD

Independent component analysis was performed for each individual CAEP gating component (Pa, P50, N1, and P2). Significant components were retained for source localization analyses within the following groups: no tinnitus, tinnitus with a THI score ≤ 6, and tinnitus with a THI score > 6. Brain source localization was performed on the gating difference wave for each component using standardized low-resolution brain electromagnetic tomography.

RESULTS

Gating-related networks were identified within each group. Different regional sources were observed between groups, with parietal sources underlying the Pa and P50 components as tinnitus severity increased. A larger prefrontal regional activation was also shown for the N1 gating component as tinnitus severity increased. These results expand upon the functional gating responses via CAEP waveforms in a previously published study.

CONCLUSIONS

The auditory gating response, as measured via CAEPs, has previously been shown to significantly correlate with an increase in tinnitus severity in adults with normal hearing. The corresponding changes in the gating response appear to be supported by different cortical regions in those without tinnitus, those with a THI score ≤ 6, and those with a THI score > 6. Next, functional differences between localized cortical regions should be tested.

Acoustic trauma increases inhibitory effects of amygdala electrical stimulation on thalamic neurons in a rat model

Acoustic trauma (AT) induced hearing loss elicits plasticity throughout the central auditory pathway, including at the level of the medial geniculate nucleus (MGN). Hearing loss also results in altered neuronal responses in the amygdala, which is involved in sensory gating at the level of the MGN. However, whether these altered responses in the amygdala affect sensory gating at the level of the MGN requires further evaluation. The current study aimed to investigate the effects of AT-induced hearing loss on the functional connectivity between the amygdala and the MGN. Male Sprague-Dawley rats were exposed to either sham (n = 5; no sound) or AT (n = 6; 16 kHz, 1 h, 124 dB SPL) under full anaesthesia. Auditory brainstem response (ABR) recordings were made to determine hearing thresholds. Two weeks post-exposure, extracellular recordings were used to assess the effect of electrical stimulation of the amygdala on tone-evoked (sham n = 22; AT n = 30) and spontaneous (sham n = 21; AT n = 29) activity of single neurons in the MGN. AT caused a large temporary and small permanent ABR threshold shift. Electrical stimulation of the amygdala induced differential effects (excitatory, inhibitory, or no effect) on both tone-evoked and spontaneous activity. In tone-evoked activity, electrical stimulation at 300 µA, maximum current, caused a significantly larger reduction in firing rate in AT animals compared to sham, due to an increase in the magnitude of inhibitory effects. In spontaneous activity, there was also a significantly larger magnitude of inhibitory effects following AT. The findings confirm that activation of the amygdala results in changes in MGN neuronal activity, and suggest the functional connectivity between the amygdala and the MGN is significantly altered following AT and subsequent hearing loss.

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.

Sensory Inhibition and Speech Perception-in-Noise Performance in Children With Normal Hearing

PURPOSE

This study investigated whether sensory inhibition in children may be associated with speech perception-in-noise performance. Additionally, gating networks associated with sensory inhibition were identified via standardized low-resolution brain electromagnetic tomography (sLORETA), and the detectability of the cortical auditory evoked potential (CAEP) N1 response was enhanced using a 4- to 30-Hz bandpass filter.

METHOD

CAEP gating responses, reflective of inhibition, were evoked via click pairs and recorded using high-density electroencephalography in neurotypical 5- to 8-year-olds and 22- to 24-year-olds. Amplitude gating indices were calculated and correlated with speech perception in noise. Gating generators were estimated using sLORETA. A 4- to 30-Hz filter was applied to detect the N1 gating component.

RESULTS

Preliminary findings indicate children showed reduced gating, but there was a correlational trend between better speech perception and decreased N2 gating. Commensurate with decreased gating, children presented with incomplete compensatory gating networks. The 4- to 30-Hz filter identified the N1 response in a subset of children.

CONCLUSIONS

There was a tenuous relationship between children's speech perception and sensory inhibition. This may suggest that sensory inhibition is only implicated in atypically poor speech perception. Finally, the 4- to 30-Hz filter settings are critical in N1 detectability.

SIGNIFICANCE

Gating may help evaluate reduced sensory inhibition in children with clinically poor speech perception using the appropriate methodology. Cortical gating generators in typically developing children are also newly identified.

Hearing Loss Increases Inhibitory Effects of Prefrontal Cortex Stimulation on Sound Evoked Activity in Medial Geniculate Nucleus

Sensory gating is the process whereby irrelevant sensory stimuli are inhibited on their way to higher cortical areas, allowing for focus on salient information. Sensory gating circuitry includes the thalamus as well as several cortical regions including the prefrontal cortex (PFC). Defective sensory gating has been implicated in a range of neurological disorders, including tinnitus, a phantom auditory perception strongly associated with cochlear trauma. Recently, we have shown in rats that functional connectivity between PFC and auditory thalamus, i.e., the medial geniculate nucleus (MGN), changes following cochlear trauma, showing an increased inhibitory effect from PFC activation on the spontaneous firing rate of MGN neurons. In this study, we further investigated this phenomenon using a guinea pig model, in order to demonstrate the validity of our finding beyond a single species and extend data to include data on sound evoked responses. Effects of PFC electrical stimulation on spontaneous and sound-evoked activity of single neurons in MGN were recorded in anaesthetised guinea pigs with normal hearing or hearing loss 2 weeks after acoustic trauma. No effect, inhibition and excitation were observed following PFC stimulation. The proportions of these effects were not different in animals with normal hearing and hearing loss but the magnitude of effect was. Indeed, hearing loss significantly increased the magnitude of inhibition for sound evoked responses, but not for spontaneous activity. The findings support previous observations that PFC can modulate MGN activity and that functional changes occur within this pathway after cochlear trauma. These data suggest hearing loss can alter sensory gating which may be a contributing factor toward tinnitus development.

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.