Functional evaluation of auditory system in patients with cochlear implant using electrically evoked auditory brainstem responses

Aim  

The objective of this study is to evaluate the recovery of hearing function of auditory pathway after cochlear implantation by extracting the characterizations of electrically evoked auditory brainstem responses (EABR). The purpose of this study was to explore a reality and possible EABR test mode in clinical applications, rather than strict animal research.     

Modulation of auditory evoked responses to spectral and temporal changes by behavioral discrimination training

Background  

Due to auditory experience, musicians have better auditory expertise than non-musicians. An increased neocortical activity during auditory oddball stimulation was observed in different studies for musicians and for non-musicians after discrimination training. This suggests a modification of synaptic strength among simultaneously active neurons due to the training. We used amplitude-modulated tones (AM) presented in an oddball sequence and manipulated their carrier or modulation frequencies. We investigated non-musicians in order to see if behavioral discrimination training could modify the neocortical activity generated by change detection of AM tone attributes (carrier or modulation frequency). Cortical evoked responses like N1 and mismatch negativity (MMN) triggered by sound changes were recorded by a whole head magnetoencephalographic system (MEG). We investigated (i) how the auditory cortex reacts to pitch difference (in carrier frequency) and changes in temporal features (modulation frequency) of AM tones and (ii) how discrimination training modulates the neuronal activity reflecting the transient auditory responses generated in the auditory cortex.     

The modulation of auditory novelty processing by working memory load in school age children and adults: a combined behavioral and event-related potential study

Background  

We investigated the processing of task-irrelevant and unexpected novel sounds and its modulation by working-memory load in children aged 9-10 and in adults. Environmental sounds (novels) were embedded amongst frequently presented standard sounds in an auditory-visual distraction paradigm. Each sound was followed by a visual target. In two conditions, participants evaluated the position of a visual stimulus (0-back, low load) or compared the position of the current stimulus with the one two trials before (2-back, high load). Processing of novel sounds were measured with reaction times, hit rates and the auditory event-related brain potentials (ERPs) Mismatch Negativity (MMN), P3a, Reorienting Negativity (RON) and visual P3b.     

Abnormal resting-state cortical coupling in chronic tinnitus

Background  

Subjective tinnitus is characterized by an auditory phantom perception in the absence of any physical sound source. Consequently, in a quiet environment, tinnitus patients differ from control participants because they constantly perceive a sound whereas controls do not. We hypothesized that this difference is expressed by differential activation of distributed cortical networks.     

Diacylglycerol kinase β promotes dendritic outgrowth and spine maturation in developing hippocampal neurons

Background  

Under natural circumstances, attention plays an important role in extracting relevant auditory signals from simultaneously present, irrelevant noises. Excitatory and inhibitory neural activity, enhanced by attentional processes, seems to sharpen frequency tuning, contributing to improved auditory performance especially in noisy environments. In the present study, we investigated auditory magnetic fields in humans that were evoked by pure tones embedded in band-eliminated noises during two different stimulus sequencing conditions (constant vs. random) under auditory focused attention by means of magnetoencephalography (MEG).     

Arithmetic mismatch negativity and numerical magnitude processing in number matching

Background

After a prolonged exposure to a paired presentation of different types of signals (e.g., color and motion), one of the signals (color) becomes a driver for the other signal (motion). This phenomenon, which is known as contingent motion aftereffect, indicates that the brain can establish new neural representations even in the adult's brain. However, contingent motion aftereffect has been reported only in visual or auditory domain. Here, we demonstrate that a visual motion aftereffect can be contingent on a specific sound.

Results

Dynamic random dots moving in an alternating right or left direction were presented to the participants. Each direction of motion was accompanied by an auditory tone of a unique and specific frequency. After a 3-minutes exposure, the tones began to exert marked influence on the visual motion perception, and the percentage of dots required to trigger motion perception systematically changed depending on the tones. Furthermore, this effect lasted for at least 2 days.

Conclusions

These results indicate that a new neural representation can be rapidly established between auditory and visual modalities.     

Auditory sustained field responses to periodic noise

Background  

Auditory sustained responses have been recently suggested to reflect neural processing of speech sounds in the auditory cortex. As periodic fluctuations below the pitch range are important for speech perception, it is necessary to investigate how low frequency periodic sounds are processed in the human auditory cortex. Auditory sustained responses have been shown to be sensitive to temporal regularity but the relationship between the amplitudes of auditory evoked sustained responses and the repetitive rates of auditory inputs remains elusive. As the temporal and spectral features of sounds enhance different components of sustained responses, previous studies with click trains and vowel stimuli presented diverging results. In order to investigate the effect of repetition rate on cortical responses, we analyzed the auditory sustained fields evoked by periodic and aperiodic noises using magnetoencephalography.     

Hemodynamic responses in human multisensory and auditory association cortex to purely visual stimulation

Background  

Recent findings of a tight coupling between visual and auditory association cortices during multisensory perception in monkeys and humans raise the question whether consistent paired presentation of simple visual and auditory stimuli prompts conditioned responses in unimodal auditory regions or multimodal association cortex once visual stimuli are presented in isolation in a post-conditioning run. To address this issue fifteen healthy participants partook in a "silent" sparse temporal event-related fMRI study. In the first (visual control) habituation phase they were presented with briefly red flashing visual stimuli. In the second (auditory control) habituation phase they heard brief telephone ringing. In the third (conditioning) phase we coincidently presented the visual stimulus (CS) paired with the auditory stimulus (UCS). In the fourth phase participants either viewed flashes paired with the auditory stimulus (maintenance, CS-) or viewed the visual stimulus in isolation (extinction, CS+) according to a 5:10 partial reinforcement schedule. The participants had no other task than attending to the stimuli and indicating the end of each trial by pressing a button.     

Auditory temporal processing in healthy aging: a magnetoencephalographic study

Background  

Impaired speech perception is one of the major sequelae of aging. In addition to peripheral hearing loss, central deficits of auditory processing are supposed to contribute to the deterioration of speech perception in older individuals. To test the hypothesis that auditory temporal processing is compromised in aging, auditory evoked magnetic fields were recorded during stimulation with sequences of 4 rapidly recurring speech sounds in 28 healthy individuals aged 20 – 78 years.     

Ear asymmetries in middle-ear, cochlear, and brainstem responses in human infants

In 2004, Sininger and Cone-Wesson examined asymmetries in the signal-to-noise ratio (SNR) of otoacoustic emissions (OAE) in infants, reporting that distortion-product (DP)OAE SNR was larger in the left ear, whereas transient-evoked (TE)OAE SNR was larger in the right. They proposed that cochlear and brainstem asymmetries facilitate development of brain-hemispheric specialization for sound processing. Similarly, in 2006 Sininger and Cone-Wesson described ear asymmetries mainly favoring the right ear in infant auditory brainstem responses (ABRs). The present study analyzed 2640 infant responses to further explore these effects. Ear differences in OAE SNR, signal, and noise were evaluated separately and across frequencies (1.5, 2, 3, and 4 kHz), and ABR asymmetries were compared with cochlear asymmetries. Analyses of ear-canal reflectance and admittance showed that asymmetries in middle-ear functioning did not explain cochlear and brainstem asymmetries. Current results are consistent with earlier studies showing right-ear dominance for TEOAE and ABR. Noise levels were higher in the right ear for OAEs and ABRs, causing ear asymmetries in SNR to differ from those in signal level. No left-ear dominance for DPOAE signal was observed. These results do not support a theory that ear asymmetries in cochlear processing mimic hemispheric brain specialization for auditory processing.     

Structural and functional effects of acoustic exposure in goldfish: evidence for tonotopy in the teleost saccule

Background  

Mammalian and avian auditory hair cells display tonotopic mapping of frequency along the length of the cochlea and basilar papilla. It is not known whether the auditory hair cells of fishes possess a similar tonotopic organization in the saccule, which is thought to be the primary auditory receptor in teleosts. To investigate this question, we determined the location of hair cell damage in the saccules of goldfish (Carassius auratus) following exposure to specific frequencies. Subjects were divided into six groups of six fish each (five treatment groups plus control). The treatment groups were each exposed to one of five tones: 100, 400, 800, 2000, and 4000 Hz at 176 dB re 1 μPa root mean squared (RMS) for 48 hours. The saccules of each fish were dissected and labeled with phalloidin in order to visualize hair cell bundles. The hair cell bundles were counted at 19 specific locations in each saccule to determine the extent and location of hair cell damage. In addition to quantification of anatomical injury, hearing tests (using auditory evoked potentials) were performed on each fish immediately following sound exposure. Threshold shifts were calculated by subtracting control thresholds from post-sound exposure thresholds.     

Asymmetric lateral inhibitory neural activity in the auditory system: a magnetoencephalographic study

Background  

Decrements of auditory evoked responses elicited by repeatedly presented sounds with similar frequencies have been well investigated by means of electroencephalography and magnetoencephalography (MEG). However the possible inhibitory interactions between different neuronal populations remains poorly understood. In the present study, we investigated the effect of proceeding notch-filtered noises (NFNs) with different frequency spectra on a following test tone using MEG.     

Toneburst-evoked auditory brainstem response in a leopard seal, Hydrurga leptonyx

Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leopard seal. Three frequencies from 1 to 4 kHz were tested at sound levels from 68 to 122 dB peak equivalent sound pressure level (peSPL). Results illustrate brainstem activity within the 1-4 kHz range, with better hearing sensitivity at 4 kHz. As is seen in human ABR, only wave V is reliably identified at the lower stimulus intensities. Wave V is present down to levels of 82 dB peSPL in the right ear and 92 dB peSPL in the left ear at 4 kHz. Further investigations testing a wider frequency range on seals of various sex and age classes are required to conclusively report on the hearing range and sensitivity in this species.     

Auditory brainstem responses to chirps delivered by an insert earphone with equalized frequency response

Recently it has been demonstrated that auditory brainstem responses, ABRs, to chirps are larger with the ER-2 than with the ER-3A insert earphone due to differences between the corresponding amplitude-frequency responses. Therefore a modified chirp, which equalizes the amplitude-frequency response of the ER-3A, is constructed and subsequently compared to the unmodified chirp. ABRs are recorded from 20 normal-hearing subjects in response to the two chirps delivered by the ER-3A earphone at a wide range of levels. The results confirm that the modified chirp generates significantly larger ABRs than the unmodified chirp at levels below 60?dB nHL.     

Visuo-auditory interactions in the primary visual cortex of the behaving monkey: Electrophysiological evidence

Background  

Visual, tactile and auditory information is processed from the periphery to the cortical level through separate channels that target primary sensory cortices, from which it is further distributed to functionally specialized areas. Multisensory integration is classically assigned to higher hierarchical cortical areas, but there is growing electrophysiological evidence in man and monkey of multimodal interactions in areas thought to be unimodal, interactions that can occur at very short latencies. Such fast timing of multisensory interactions rules out the possibility of an origin in the polymodal areas mediated through back projections, but is rather in favor of heteromodal connections such as the direct projections observed in the monkey, from auditory areas (including the primary auditory cortex AI) directly to the primary visual cortex V1. Based on the existence of such AI to V1 projections, we looked for modulation of neuronal visual responses in V1 by an auditory stimulus in the awake behaving monkey.     

Differential responses to acoustic damage and furosemide in auditory brainstem and otoacoustic emission measures

Characteristics of distortion product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs) were measured in Mongolian gerbil before and after the introduction of two different auditory dysfunctions: (1) acoustic damage with a high-intensity tone, or (2) furosemide intoxication. The goal was to find emission parameters and measures that best differentiated between the two dysfunctions, e.g., at a given ABR threshold elevation. Emission input-output or "growth" functions were used (frequencies f1 and f2, f2/f1 = 1.21) with equal levels, L1 = L2, and unequal levels, with L1 = L2 + 20 dB. The best parametric choice was found to be unequal stimulus levels, and the best measure was found to be the change in the emission threshold level, delta x. The emission threshold was defined as the stimulus level required to reach a criterion emission amplitude, in this case -10 dB SPL. (The next best measure was the change in emission amplitude at high stimulus levels, specifically that measured at L1 x L2 = 90 x 70 dB SPL.) For an ABR threshold shift of 20 dB or more, there was essentially no overlap in the emission threshold measures for the two conditions, sound damage or furosemide. The dividing line between the two distributions increased slowly with the change in ABR threshold, delta ABR, and was given by delta x(t) = 0.6 delta ABR + 8 dB. For a given delta ABR, if the shift in emission threshold was more than the calculated dividing line value, delta x(t), the auditory dysfunction was due to acoustic damage, if less, it was due to furosemide.     

The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side

Background  

In normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes.     

Asymmetrical hippocampal connectivity in mesial temporal lobe epilepsy: evidence from resting state fMRI

Background

Recent studies have shown that the human right-hemispheric auditory cortex is particularly sensitive to reduction in sound quality, with an increase in distortion resulting in an amplification of the auditory N1m response measured in the magnetoencephalography (MEG). Here, we examined whether this sensitivity is specific to the processing of acoustic properties of speech or whether it can be observed also in the processing of sounds with a simple spectral structure. We degraded speech stimuli (vowel /a/), complex non-speech stimuli (a composite of five sinusoidals), and sinusoidal tones by decreasing the amplitude resolution of the signal waveform. The amplitude resolution was impoverished by reducing the number of bits to represent the signal samples. Auditory evoked magnetic fields (AEFs) were measured in the left and right hemisphere of sixteen healthy subjects.

Results

We found that the AEF amplitudes increased significantly with stimulus distortion for all stimulus types, which indicates that the right-hemispheric N1m sensitivity is not related exclusively to degradation of acoustic properties of speech. In addition, the P1m and P2m responses were amplified with increasing distortion similarly in both hemispheres. The AEF latencies were not systematically affected by the distortion.

Conclusions

We propose that the increased activity of AEFs reflects cortical processing of acoustic properties common to both speech and non-speech stimuli. More specifically, the enhancement is most likely caused by spectral changes brought about by the decrease of amplitude resolution, in particular the introduction of periodic, signal-dependent distortion to the original sound. Converging evidence suggests that the observed AEF amplification could reflect cortical sensitivity to periodic sounds.     

A transition from unimodal to multimodal activations in four sensory modalities in humans: an electrophysiological study

Background  

To investigate the long-latency activities common to all sensory modalities, electroencephalographic responses to auditory (1000 Hz pure tone), tactile (electrical stimulation to the index finger), visual (simple figure of a star), and noxious (intra-epidermal electrical stimulation to the dorsum of the hand) stimuli were recorded from 27 scalp electrodes in 14 healthy volunteers.     

Early visual evoked potentials are modulated by eye position in humans induced by whole body rotations

Background  

To reach and grasp an object in space on the basis of its image cast on the retina requires different coordinate transformations that take into account gaze and limb positioning. Eye position in the orbit influences the image's conversion from retinotopic (eye-centered) coordinates to an egocentric frame necessary for guiding action. Neuroimaging studies have revealed eye position-dependent activity in extrastriate visual, parietal and frontal areas that is along the visuo-motor pathway. At the earliest vision stage, the role of the primary visual area (V1) in this process remains unclear. We used an experimental design based on pattern-onset visual evoked potentials (VEP) recordings to study the effect of eye position on V1 activity in humans.