Auditory Evoked Potentials In Response Research Articles

EEG study of attention on an auditory target detection task in dolphins and humans

How do dolphins attend to echos and ignore background noise? Is the process similar to how humans attend to conversations in a crowded room? Studies of human selective attention have highlighted endogenous brain processes modulating the magnitude of early responses to sounds in auditory evoked potentials (AEPs), yet these rely on task-specific instructions difficult to employ in animal studies. We trained an adult male dolphin (Tursiops truncatus) to attend to a stream of rapidly presented tones, and provide a whistle response to a “target” tone while withholding responses to “background” tones in an amplitude discrimination task. The background sounds were designed to function as a tonal mismatch negativity paradigm with two frequencies: a standard tone presented 80% of the time, and a deviant presented 20% of the time. Depending on condition, the target could be the same frequency as the standard or the deviant. We observed an enhanced AEP response to a deviant of the same frequency as the target, while the AEP response to the standard-target condition was reduced. This was not predicted by previous human experiments, and we are currently following up with a pilot a human task modeled after the dolphin implicit target detection task.

Early Auditory Event Related Potentials Distinguish Higher-Order From First-Order Aversive Conditioning.

Stimuli in reality rarely co-occur with primary reward or punishment to allow direct associative learning of value. Instead, value is thought to be inferred through complex higher-order associations. Rodent research has demonstrated that the formation and maintenance of first-order and higher-order associations are supported by distinct neural substrates. In this study, we explored whether this pattern of findings held true for humans. Participants underwent first-order and subsequent higher-order conditioning using an aversive burst of white noise or neutral tone as the unconditioned stimuli. Four distinct tones, initially neutral, served as first-order and higher-order conditioned stimuli. Autonomic and neural responses were indexed by pupillometry and evoked response potentials (ERPs) respectively. Conditioned aversive values of first-order and higher-order stimuli led to increased autonomic responses, as indexed by pupil dilation. Distinct temporo-spatial auditory evoked response potentials were elicited by first-order and high-order conditioned stimuli. Conditioned first-order responses peaked around 260 ms and source estimation suggested a primary medial prefrontal and amygdala source. Conversely, conditioned higher-order responses peaked around 120 ms with an estimated source in the medial temporal lobe. Interestingly, pupillometry responses to first-order conditioned stimuli were diminished after higher order training, possibly signifying concomitant incidental extinction, while responses to higher-order stimuli remained. This suggests that once formed, higher order associations are at least partially independent of first order conditioned representations. This experiment demonstrates that first-order and higher-order conditioned associations have distinct neural signatures, and like rodents, the medial temporal lobe may be specifically involved with higher-order conditioning.

Diagnosis of hearing deficiency using EEG based AEP signals: CWT and improved-VGG16 pipeline.

Hearing deficiency is the world’s most common sensation of impairment and impedes human communication and learning. Early and precise hearing diagnosis using electroencephalogram (EEG) is referred to as the optimum strategy to deal with this issue. Among a wide range of EEG control signals, the most relevant modality for hearing loss diagnosis is auditory evoked potential (AEP) which is produced in the brain’s cortex area through an auditory stimulus. This study aims to develop a robust intelligent auditory sensation system utilizing a pre-train deep learning framework by analyzing and evaluating the functional reliability of the hearing based on the AEP response. First, the raw AEP data is transformed into time-frequency images through the wavelet transformation. Then, lower-level functionality is eliminated using a pre-trained network. Here, an improved-VGG16 architecture has been designed based on removing some convolutional layers and adding new layers in the fully connected block. Subsequently, the higher levels of the neural network architecture are fine-tuned using the labelled time-frequency images. Finally, the proposed method’s performance has been validated by a reputed publicly available AEP dataset, recorded from sixteen subjects when they have heard specific auditory stimuli in the left or right ear. The proposed method outperforms the state-of-art studies by improving the classification accuracy to 96.87% (from 57.375%), which indicates that the proposed improved-VGG16 architecture can significantly deal with AEP response in early hearing loss diagnosis.

Detection and classification of long-latency own-name auditory evoked potential from electroencephalogram

Auditory Evoked Potential (AEP) is an electrophysiological signal elicited from the brain while an auditory stimulus is presented in a time-locked manner. Previous studies reported the occurrence of AEPs in response to different audio stimuli during the time interval up to 600 ms from the onset of the stimulus. In this paper, we report the occurrence and detection of long-latency AEPs, around 1.5 s after the onset of the stimulus, from the Electroencephalogram (EEG) acquired when the participants listen to voice clips of their own-name. The trial averaged AEPs of 24 participants who listened to audio stimuli of their own-name and familiar-names clearly showed the occurrence of a distinct negative peak around 1.5 s after the onset of the own-name stimulus in Fp1 and F7 EEG electrodes. No such long-latency AEPs were observed when the participants listened to familiar-name stimulus. We classified the own-name and familiar-name averaged AEP responses using a quadratic kernel support vector machine (SVM) classifier. The leave-one-participant-out cross-validation was performed, and the classification accuracy achieved is 80.56 % (corresponding to averaging of 8AEP responses) with a sensitivity of 68.52 % and a specificity of 92.59 %. Our study reveals the occurrence of a distinct long-latency AEP around 1.5 s for own-name stimulus and a higher discrimination ability of participants in discarding non-self-referential stimuli (familiar-name) compared to self-referential stimuli (own-name). The method can be applied for the off-line analysis of own-name AEPs to diagnose mild cognitive impairments and also developmental disorders like autism.

Assessing the integrity of auditory processing and sensory memory in adults with cystinosis (CTNS gene mutations)

BackgroundCystinosis, a rare lysosomal storage disease, is characterized by cystine crystallization and accumulation within tissues and organs, including the kidneys and brain. Its impact on neural function appears mild relative to its effects on other organs, but therapeutic advances have led to substantially increased life expectancy, necessitating deeper understanding of its impact on neurocognitive function in adulthood. We previously demonstrated intact auditory sensory processing, accompanied by mild sensory memory difficulties, in children and adolescents with cystinosis.MethodsWe investigated whether further progressive decrements in these processes would be observed in adults with cystinosis, comparing high-density auditory-evoked potential (AEP) recordings from adults with cystinosis (N = 15; ages: 19–38 years) to those of age-matched controls (N = 17). We employed a duration oddball paradigm with different stimulation rates, in which participants passively listened to regularly occurring standard tones interspersed with infrequently occurring deviant tones. Analyses focused on AEP components reflecting auditory sensory-perceptual processing (N1 and P2), sensory memory (mismatch negativity, MMN), and attentional orienting (P3a).ResultsOverall, adults with cystinosis produced highly similar sensory-perceptual AEP responses to those observed in controls suggesting intact early auditory cortical processing. However, significantly increased P2 and P3a amplitudes and reduced MMN at slower stimulation rates were observed, suggesting mild-to-moderate changes in auditory sensory memory and attentional processing. While cognitive testing revealed lower scores on verbal IQ and perceptual reasoning in cystinosis, these did not correlate with the AEP measures.ConclusionsThese neurophysiological data point to the emergence of subtle auditory processing deficits in early adulthood in cystinosis, warranting further investigation of memory and attentional processes in this population, and of their consequences for perceptual and cognitive function.

Sound detection by the American lobster (Homarus americanus).

Although many crustaceans produce sounds, their hearing abilities and mechanisms are poorly understood, leaving uncertainties regarding whether or how these animals use sound for acoustic communication. Marine invertebrates lack gas-filled organs required for sound pressure detection, but some of them are known to be sensitive to particle motion. Here, we examined whether the American lobster (Homarus americanus) could detect sound and subsequently sought to discern the auditory mechanisms. Acoustic stimuli responses were measured using auditory evoked potential (AEP) methods. Neurophysiological responses were obtained from the brain using tone pips between 80 and 250 Hz, with best sensitivity at 80-120 Hz. There were no significant differences between the auditory thresholds of males and females. Repeated controls (recordings from deceased lobsters, moving electrodes away from the brain and reducing seawater temperature) indicated the evoked potentials' neuronal origin. In addition, AEP responses were similar before and after antennules (including statocysts) were ablated, demonstrating that the statocysts, a long-proposed auditory structure in crustaceans, are not the sensory organs responsible for lobster sound detection. However, AEPs could be eliminated (or highly reduced) after immobilizing hairfans, which cover much of lobster bodies. These results suggest that these external cuticular hairs are likely to be responsible for sound detection, and imply that hearing is mechanistically possible in a wider array of invertebrates than previously considered. Because the lobsters' hearing range encompasses the fundamental frequency of their buzzing sounds, it is likely that they use sound for intraspecific communication, broadening our understanding of the sensory ecology of this commercially vital species. The lobsters' low-frequency acoustic sensitivity also underscores clear concerns about the potential impacts of anthropogenic noise.

Latency-dependent filtering and compact representation of the complete auditory pathway response.

Auditory evoked potentials (AEPs) include the auditory brainstem response (ABR), middle latency response (MLR), and cortical auditory evoked potentials (CAEPs), each one covering a specific latency range and frequency band. For this reason, ABR, MLR, and CAEP are usually recorded separately using different protocols. This article proposes a procedure providing a latency-dependent filtering and down-sampling of the AEP responses. This way, each AEP component is appropriately filtered, according to its latency, and the complete auditory pathway response is conveniently represented (with the minimum number of samples, i.e., without unnecessary redundancies). The compact representation of the complete response facilitates a comprehensive analysis of the evoked potentials (keeping the natural continuity related to the neural activity transmission along the auditory pathway), which provides a new perspective in the design and analysis of AEP experiments. Additionally, the proposed compact representation reduces the storage or transmission requirements when large databases are manipulated for clinical or research purposes. The analysis of the AEP responses shows that a compact representation with 40 samples/decade (around 120 samples) is enough for accurately representing the response of the complete auditory pathway and provides appropriate latency-dependent filtering. MatLab/Octave code implementing the proposed procedure is included in the supplementary materials.

FUNCTIONAL NEUROCOGNITIVE DEFICITS AND CORTICAL EVOKED POTENTIALS IN PEDIATRIC PATIENTS WITH PROLONGED POST CONCUSSIVE SYMPTOMS

Background: Prolonged neurophysiological impairments have been demonstrated after brain injury utilizing tools such as auditory evoked response potentials. The objectivity and sensitivity of such tools can provide clinicians a unique perspective on patients with prolonged post concussive symptoms (PPCS), and help determine optimal management strategies. Limited research currently exists on evoked potentials and pediatric PPCS. Purpose: Illustrate the clinical utility of abnormal evoked potentials in adolescents with PPCS. Methods and Study Design: The study is a retrospective cross-sectional analysis of pediatric PPCS cases from 7/2018 to 7/2019 at a private concussion clinic in Tucson AZ. Patients were included if they had prolonged symptoms beyond 30 days from date of injury date, were 13-16 years old, and diagnosed with PPCS based on SCAT5 assessment and clinical evaluation. All patients with PPCS had moderate to severe clinical symptoms with limited academic and exertional tolerance. Patients were excluded if they had a history of learning disorders, seizure disorder, or complex concussions with a skull fracture or intracranial hemorrhage. Patients were tested using the standard oddball audio P300 EEG protocol. Measures extracted included P300 latency, P300 amplitude, and coherence frequency on mapping. The PPCS cohort (n=71) was then compared to age-matched references (n=73) obtained during baseline testing of non-injured athletes using the same protocol (and hardware) from a multitude of sites. Results: There was a significant correlation between PPCS and reduced P300 amplitude along with an increased coherence. The PPCS group had an average P300 amplitude of 13.7uV compared to 16.9uV in the reference group (p<0.001, CohD=.51). Increased coherence (in the alpha frequency) was observed where the average PPCS patient had 9.1 connected pairs (scalp sites) with coherences that were >2σ, compared to the expected 3.1 connections in reference group >2 σ (p<0.001, CohD=.86). There was no significant difference in P300 latency between the groups. Conclusions: Pediatric patients with PPCS showed decreased P300 amplitude and increased coherence on average compared to the reference group. Reduced voltages and/or increased coherence likely represent ongoing primary brain dysfunction, adaptability, and recovery. These findings suggest the need for ongoing care, and should guide a conservative care approach towards return to high-risk activities. Evoked potentials may be a critical tool to help identify primary neurologic dysfunction in PPCS and help guide management strategies. This tool may also aide in differentiating ongoing neurophysiologic recovery from commonly reported secondary psychosocial symptoms after PPCS. [Figure: see text]

The effect of experience with phonological sequences on the suppression effect, used to assess echoic sensory memory, within the auditory‐evoked potentials (AEPs)

Specific Language Impairment (SLI), a developmental language disorder, has been associated with deficits in working memory (Gathercole, 2006). Using magnetoencephalography (MEG), Helenius and colleagues (2009, 2014) have shown that adults and children with SLI have impaired sensory memory for the repetition of meaningful spoken words. Also, of interest is whether individuals with SLI show impaired sensory memory for phonological sequences, which would likely affect vocabulary learning. As a first step in pursuing this question, we examined the effects of experience with phonological sequences on the suppression effect used to assess sensory memory. The suppression effect, is a reduced response within the auditory evoked potentials (AEPs) or its magnetic counterpart, to repetition of an auditory event, including phonological sequences. EEGs were recorded from 24 native‐English and 24 native‐Polish adults as they listened to same and different non‐word pairs within two experimental sessions. Non‐word pairs contained a phonological sequence contrast, /st‐sət/that occurs in the English and Polish languages and a contrast /pt‐pət/that occurs only in the Polish language. The EEG was time locked to the second word in the non‐word pairs, which was the same non‐word in the same pairs (pətilɑ‐pətilɑ) and different pairs (ptilɑ‐pətilɑ). Thus, a larger AEP response to the second word in the different pairs relative to the second word in the same pairs indicates that the brain registered the additional sound in the different pair. Likewise, evidence of the suppression effect within the same pairs suggest an intact sensory memory for the phonological sequences within the first non‐word. Preliminary examination of results at averaged fronto‐central electrode sites within the AEP revealed an effect of language experience between ~400–600 ms post‐word onset. The native‐Polish listeners showed a larger response to their native language /pt‐pət/contrast than the English listeners and the English listeners showed a larger response to the /st‐sət/contrast that is more prominent in the English language than the Polish language. Thus, native‐language experience and frequency of phonological sequences within a language should be considered when assessing sensory memory in clinical populations.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Auditory evoked potentials of the plainfin midshipman fish (Porichthys notatus): implications for directional hearing.

The plainfin midshipman (Porichthys notatus) is an acoustically communicative teleost fish. Here, we evaluated auditory evoked potentials (AEPs) in reproductive female midshipman exposed to tones at or near dominant frequencies of the male midshipman advertisement call. An initial series of experiments characterized AEPs at behaviorally relevant suprathreshold sound levels (130-140 dB SPL re. 1 µPa). AEPs decreased in magnitude with increasing stimulus frequency and featured a stereotyped component at twice the stimulus frequency. Recording electrode position was varied systematically and found to affect AEP magnitude and phase characteristics. Later experiments employed stimuli of a single frequency to evaluate contributions of the saccule to the AEP, with particular attention to the effects of sound source azimuth on AEP amplitude. Unilateral excision of saccular otoliths (sagittae) decreased AEP amplitude; unexpectedly, decreases differed for right versus left otolith excision. A final set of experiments manipulated the sound pressure-responsive swim bladder. Swim bladder excision further reduced the magnitude of AEP responses, effectively eliminating responses at the standard test intensity (130 dB SPL) in some animals. Higher-intensity stimulation yielded response minima at forward azimuths ipsilateral to the excised sagitta, but average cross-azimuth modulation generally remained slight. Collectively, the data underscore that electrode position is an essential variable to control in fish AEP studies and suggest that in female midshipman: (1) the saccule contributes to the AEP, but its directionality as indexed by the AEP is limited, (2) a left-right auditory asymmetry may exist and (3) the swim bladder provides gain in auditory sensitivity that may be important for advertisement call detection and phonotaxis.

The cognitive resource and foreknowledge dependence of auditory perceptual inference

Auditory perceptual inference engages learning of complex statistical information about the environment. Inferences assist us to simplify perception highlighting what can be predicted on the basis of prior learning (through the formation of internal “prediction” models) and what might be new, potentially necessitating an investment of resources to remodel predictions. In the present study, we tested the hypothesis that sound sequences with multiple levels of predictability may rely on cognitive resources and be cognitively penetrable to a greater extent than was previously shown by studies presenting simpler sound sequences. Auditory-evoked potentials (AEPs) were recorded from 117 participants. All participants heard the exact same sound sequence but under different conditions: 51 while watching a DVD movie and 66 while performing a cognitively demanding task. Participants were asked to ignore the sounds and focus their attention on the movie/task. However, prior to commencing the experiment we manipulated what participants knew about the sound sequence by providing explicit sequence information to 15 and 34 of the participants in the DVD and cognitive-task conditions, respectively, and no information to the others. The results demonstrated that although local pattern violations elicited distinctive AEP responses (namely, mismatch negativity), the way the amplitude of this response was modulated by sequence learning over time was dependent upon both task and explicit sequence knowledge. The implications are discussed with reference to how the division of available attention resources between the primary task and concurrent sound impacts what is learned.

Roles of Prefrontal Cortex and Mediodorsal Thalamus in Task Engagement and Behavioral Flexibility

Behavioral tasks involving auditory cues activate inhibitory neurons within auditory cortex, leading to a reduction in the amplitude of auditory evoked response potentials (ERPs). One hypothesis is that this process, termed "task engagement," may enable context-dependent behaviors. Here we set out to determine (1) whether the medial prefrontal cortex (mPFC) plays a role in task engagement and (2) how task engagement relates to the context-dependent processing of auditory cues in male and female mice performing a decision-making task that can be guided by either auditory or visual cues. We found that, in addition to auditory ERP suppression, task engagement is associated with increased mPFC activity and an increase in theta band (4-7 Hz) synchronization between the mPFC and auditory cortex. Optogenetically inhibiting the mPFC eliminates the task engagement-induced auditory ERP suppression, while also preventing mice from switching between auditory and visual cue-based rules. However, mPFC inhibition, which eliminates task engagement-induced auditory ERP suppression, did not prevent mice from making decisions based on auditory cues. Furthermore, a more specific manipulation, selective disruption of mPFC outputs to the mediodorsal (MD) thalamus, is sufficient to prevent switching between auditory and visual rules but does not affect auditory ERPs. Based on these findings, we conclude that (1) the mPFC contributes to both task engagement and behavioral flexibility; (2) mPFC-MD projections are important for behavioral flexibility but not task engagement; and (3) task engagement, evidenced by the suppression of cortical responses to sensory input, is not required for sensory cue-guided decision making.SIGNIFICANCE STATEMENT When rodents perform choice-selection tasks based on sensory cues, neural responses to these cues are modulated compared with task-free conditions. Here we demonstrate that this phenomenon depends on the prefrontal cortex and thus represents a form of "top-down" regulation. However, we also show that this phenomenon is not critical for task performance, as rodents can make decisions based on specific sensory cues even when the task-dependent modulation of responses to those cues is abolished. Furthermore, disrupting one specific set of prefrontal outputs impairs rule switching but not the task-dependent modulation of sensory responses. These results show that the prefrontal cortex comprises multiple circuits that mediate dissociable functions related to behavioral flexibility and sensory processing.

Cortical Auditory-Evoked Potentials in Response to Multitone Stimuli in Hearing-Impaired Adults.

To determine if one-octave multitone (MT) stimuli increase the amplitude of cortical auditory-evoked potentials (CAEPs) in individuals with a hearing loss when compared to standard pure-tone (PT) stimuli and narrow-band noise (NBN). CAEPs were obtained from 16 hearing-impaired adults in response to PT and MT auditory stimuli centered around 0.5, 1, 2, and 4 kHz and NBN centered around 1 and 2 kHz. Hearing impairment ranged from a mild to a moderate hearing loss in both ears. Auditory stimuli were monaurally delivered through insert earphones at 10 and 20 dB above threshold. The root mean square amplitude of the CAEP and the detectability of the responses using Hotelling's T² were calculated and analyzed. CAEP amplitudes elicited with MT stimuli were on average 29% larger than PT stimuli for frequencies centered around 1, 2, and 4 kHz. No significant difference was found for responses to 0.5-kHz stimuli. Significantly higher objective detection scores were found for MT when compared to PT. For the 1- and 2-kHz stimuli, the CAEP amplitudes to NBN were not significantly different to those evoked by PT but a significant difference was found between MT stimuli and both NBN and PT. The mean detection sensitivity of MT for the four frequencies was 80% at 10 dB SL and 95% at 20 dB SL, and was comparable with detection sensitivities observed in normal-hearing participants. Using MT stimuli when testing CAEPs in adults with hearing impairment showed larger amplitudes and a higher objective detection sensitivity compared to using traditional PT stimuli for frequencies centered around 1, 2, and 4 kHz. These findings suggest that MT stimuli are a clinically useful tool to increase the efficiency of frequency-specific CAEP testing in adults with hearing impairment.

Auditory evoked potential response and hearing loss: a review.

Hypoacusis is the most prevalent sensory disability in the world and consequently, it can lead to impede speech in human beings. One best approach to tackle this issue is to conduct early and effective hearing screening test using Electroencephalogram (EEG). EEG based hearing threshold level determination is most suitable for persons who lack verbal communication and behavioral response to sound stimulation. Auditory evoked potential (AEP) is a type of EEG signal emanated from the brain scalp by an acoustical stimulus. The goal of this review is to assess the current state of knowledge in estimating the hearing threshold levels based on AEP response. AEP response reflects the auditory ability level of an individual. An intelligent hearing perception level system enables to examine and determine the functional integrity of the auditory system. Systematic evaluation of EEG based hearing perception level system predicting the hearing loss in newborns, infants and multiple handicaps will be a priority of interest for future research.

The investigation of cortical auditory evoked potentials responses in young adults having musical education.

In the literature, music education has been shown to enhance auditory perception for children and young adults. When compared to young adult non-musicians, young adult musicians demonstrate increased auditory processing, and enhanced sensitivity to acoustic changes. The evoked response potentials associated with the interpretation of sound are enhanced in musicians. Studies show that training also changes sound perception and cortical responses. The earlier training appears to lead to larger changes in the auditory cortex. Most cortical studies in the literature have used pure tones or musical instrument sounds as stimuli signals. The aim of those studies was to investigate whether musical education would enhance auditory cortical responses when speech signals were used. In this study, the speech sounds extracted from running speech were used as sound stimuli. Non-randomized controlled study. The experimental group consists of young adults up to 21 years-old, all with a minimum of 4 years of musical education. The control group was selected from young adults of the same age without any musical education. The experiments were conducted by using a cortical evoked potential analyser and /m/, /t/ /g/ sound stimulation at the level of 65 dB SPL. In this study, P1 / N1 / P2 amplitude and latency values were measured. Significant differences were found in the amplitude values of P1 and P2 (p<0.05). The differences among the latencies were not found to be significantly important (p>0.05). The results obtained in our study indicate that musical experience has an effect on the nervous system and this can be seen in cortical auditory evoked potentials recorded when the subjects hear speech.

Towards neural correlates of auditory stimulus processing: A simultaneous auditory evoked potentials and functional magnetic resonance study using an odd-ball paradigm

BackgroundThe neural underpinnings of auditory information processing have often been investigated using the odd-ball paradigm, in which infrequent sounds (deviants) are presented within a regular train of frequent stimuli (standards). Traditionally, this paradigm has been applied using either high temporal resolution (EEG) or high spatial resolution (fMRI, PET). However, used separately, these techniques cannot provide information on both the location and time course of particular neural processes. The goal of this study was to investigate the neural correlates of auditory processes with a fine spatio-temporal resolution. A simultaneous auditory evoked potentials (AEP) and functional magnetic resonance imaging (fMRI) technique (AEP-fMRI), together with an odd-ball paradigm, were used.Material/MethodsSix healthy volunteers, aged 20–35 years, participated in an odd-ball simultaneous AEP-fMRI experiment. AEP in response to acoustic stimuli were used to model bioelectric intracerebral generators, and electrophysiological results were integrated with fMRI data.ResultsfMRI activation evoked by standard stimuli was found to occur mainly in the primary auditory cortex. Activity in these regions overlapped with intracerebral bioelectric sources (dipoles) of the N1 component. Dipoles of the N1/P2 complex in response to standard stimuli were also found in the auditory pathway between the thalamus and the auditory cortex. Deviant stimuli induced fMRI activity in the anterior cingulate gyrus, insula, and parietal lobes.ConclusionsThe present study showed that neural processes evoked by standard stimuli occur predominantly in subcortical and cortical structures of the auditory pathway. Deviants activate areas non-specific for auditory information processing.

Repetition suppression of the rat auditory evoked potential at brief stimulus intervals

An important prerequisite for the development of animal models of human auditory evoked potentials (AEP) is the accurate identification of homology. Prior research has revealed some remarkably similar response properties between rat and human AEPs, although there remains little consensus regarding the nature or validity of this correspondence. In the present study we seek to extend this research by examining the response properties of rat AEP as a function of stimulus repetition and interval. The aim being to determine whether rat AEP components show the same paradoxical reversal of repetition suppression observed for the human N100 AEP component at brief stimulus intervals. To achieve this, AEPs were recorded epidurally at the vertex in the freely moving rat in response to acoustic stimuli presented at random stimulus intervals between 50 and 5000ms. Using stimulation and analysis techniques to remove AEP waveform distortion due to overlapping AEP responses, the present results show that rat AEP components can be successfully resolved at intervals as brief as 50ms. The results also demonstrate several fundamental types of correspondence between human and rat AEP components in terms of the sensitivity to stimulus interval and acoustic stimulus type. However the results found no evidence that rat AEP components show the reversal of repetition suppression at brief, relative to long, stimulus intervals as demonstrated for the N100 component in humans. The results are discussed in terms of EEG recording and AEP analysis procedures that provide promising avenues for future research.

Overcompensation of echo attenuation and dual-component biosonar control in echolocation of an Atlantic bottlenose dolphin (Tursiops truncatus)

Transmitting biosonar clicks and auditory evoked potential (AEP) responses triggered by the clicks were synchronously recorded during echolocation in an Atlantic bottlenose dolphin (Tursiops truncatus) trained to wear suction-cup EEG electrodes and to detect targets by echolocation. Three targets with target strengths of −34, −28 and −22 dB were used at a target distance of 2 to 6.5 m for each target. The results demonstrated that the AEP appeared to both transmitting echolocation clicks and echoes during echolocation, with AEP complexes consisting of alternative positive and negative waves. The echo-related AEP amplitudes were obviously lower than the transmitting click-related AEP amplitudes for all the targets at the investigated target distances. However, for targets with target strengths of −22 and −28 dB, the echo-related AEP response amplitudes increased at further target distances, demonstrating an overcompensation of echo attenuation with target distance in the echo-perception system of the dolph...

Hearing Sensation Levels of Emitted Biosonar Clicks in an Echolocating Atlantic Bottlenose Dolphin

Emitted biosonar clicks and auditory evoked potential (AEP) responses triggered by the clicks were synchronously recorded during echolocation in an Atlantic bottlenose dolphin (Tursiops truncatus) trained to wear suction-cup EEG electrodes and to detect targets by echolocation. Three targets with target strengths of −34, −28, and −22 dB were used at distances of 2 to 6.5 m for each target. The AEP responses were sorted according to the corresponding emitted click source levels in 5-dB bins and averaged within each bin to extract biosonar click-related AEPs from noise. The AEP amplitudes were measured peak-to-peak and plotted as a function of click source levels for each target type, distance, and target-present or target-absent condition. Hearing sensation levels of the biosonar clicks were evaluated by comparing the functions of the biosonar click-related AEP amplitude-versus-click source level to a function of external (in free field) click-related AEP amplitude-versus-click sound pressure level. The results indicated that the dolphin's hearing sensation levels to her own biosonar clicks were equal to that of external clicks with sound pressure levels 16 to 36 dB lower than the biosonar click source levels, varying with target type, distance, and condition. These data may be assumed to indicate that the bottlenose dolphin possesses effective protection mechanisms to isolate the self-produced intense biosonar beam from the animal's ears during echolocation.

Semi-automatic attenuation of cochlear implant artifacts for the evaluation of late auditory evoked potentials

Electrical artifacts caused by the cochlear implant (CI) contaminate electroencephalographic (EEG) recordings from implanted individuals and corrupt auditory evoked potentials (AEPs). Independent component analysis (ICA) is efficient in attenuating the electrical CI artifact and AEPs can be successfully reconstructed. However the manual selection of CI artifact related independent components (ICs) obtained with ICA is unsatisfactory, since it contains expert-choices and is time consuming.We developed a new procedure to evaluate temporal and topographical properties of ICs and semi-automatically select those components representing electrical CI artifact. The CI Artifact Correction (CIAC) algorithm was tested on EEG data from two different studies. The first consists of published datasets from 18 CI users listening to environmental sounds. Compared to the manual IC selection performed by an expert the sensitivity of CIAC was 91.7% and the specificity 92.3%. After CIAC-based attenuation of CI artifacts, a high correlation between age and N1–P2 peak-to-peak amplitude was observed in the AEPs, replicating previously reported findings and further confirming the algorithm's validity.In the second study AEPs in response to pure tone and white noise stimuli from 12 CI users that had also participated in the other study were evaluated. CI artifacts were attenuated based on the IC selection performed semi-automatically by CIAC and manually by one expert. Again, a correlation between N1 amplitude and age was found. Moreover, a high test–retest reliability for AEP N1 amplitudes and latencies suggested that CIAC-based attenuation reliably preserves plausible individual response characteristics.We conclude that CIAC enables the objective and efficient attenuation of the CI artifact in EEG recordings, as it provided a reasonable reconstruction of individual AEPs. The systematic pattern of individual differences in N1 amplitudes and latencies observed with different stimuli at different sessions, strongly suggests that CIAC can overcome the electrical artifact problem. Thus CIAC facilitates the use of cortical AEPs as an objective measurement of auditory rehabilitation.