Auditory-evoked Responses Research Articles

Latency variation of auditory N1m responses to vocal and nonvocal sounds

To investigate the temporal aspect of timbre processing, we recorded auditory-evoked neuromagnetic responses to periodic complex sounds, which were matched in all acoustic parameters except for two fundamental frequencies (F0s) and 12 spectral envelopes of vocal and nonvocal categories. Only for nonvocal sounds, a significant difference in N1m latency for F0 was detected in both hemispheres. A significant difference among stimuli was detected in both hemispheres for vocal and linear sounds, whereas only in the right hemisphere for instrumental sounds. Moreover, the results of paired comparison among F0s revealed that not only the vocal sounds but also some of the nonvocal sounds were F0-independent. This latency independence may be attributed to the relatively high power in the higher frequency spectrum.

Threshold and Beyond: Modeling The Intensity Dependence of Auditory Responses

In many studies of auditory-evoked responses to low-intensity sounds, the response amplitude appears to increase roughly linearly with the sound level in decibels (dB), corresponding to a logarithmic intensity dependence. But the auditory system is assumed to be linear in the low-intensity limit. The goal of this study was to resolve the seeming contradiction. Based on assumptions about the rate-intensity functions of single auditory-nerve fibers and the pattern of cochlear excitation caused by a tone, a model for the gross response of the population of auditory nerve fibers was developed. In accordance with signal detection theory, the model denies the existence of a threshold. This implies that regarding the detection of a significant stimulus-related effect, a reduction in sound intensity can always be compensated for by increasing the measurement time, at least in theory. The model suggests that the gross response is proportional to intensity when the latter is low (range I), and a linear function of sound level at higher intensities (range III). For intensities in between, it is concluded that noisy experimental data may provide seemingly irrefutable evidence of a linear dependence on sound pressure (range II). In view of the small response amplitudes that are to be expected for intensity range I, direct observation of the predicted proportionality with intensity will generally be a challenging task for an experimenter. Although the model was developed for the auditory nerve, the basic conclusions are probably valid for higher levels of the auditory system, too, and might help to improve models for loudness at threshold.

Aging in Binaural Hearing Begins in Mid-Life: Evidence from Cortical Auditory-Evoked Responses to Changes in Interaural Phase

Older adults often have difficulty understanding speech in a noisy environment or with multiple speakers. In such situations, binaural hearing improves the signal-to-noise ratio. How does this binaural advantage change with increasing age? Using magnetoencephalography, we recorded cortical activity evoked by changes in interaural phase differences of amplitude-modulated tones. These responses occurred for frequencies up to 1225 Hz in young subjects but only up to 940 Hz in middle-aged and 760 Hz in older adults. Behavioral thresholds also decreased with increasing age but were more variable, likely because some older adults make effective use of compensatory mechanisms. The reduced frequency range for binaural hearing became significant in middle age, before decline in hearing sensation and the morphology of cortical responses, which became apparent only in the older subjects. This study provides evidence from human physiological data for the early onset of biological aging in binaural hearing.

Activation of the serotonin 1A receptor alters the temporal characteristics of auditory responses in the inferior colliculus

Serotonin, like other neuromodulators, acts on a range of receptor types, but its effects also depend on the functional characteristics of the neurons responding to receptor activation. In the inferior colliculus (IC), an auditory midbrain nucleus, activation of a common serotonin (5-HT) receptor type, the 5-HT 1A receptor, depresses auditory-evoked responses in many neurons. Whether these effects occur differentially in different types of neurons is unknown. In the current study, the effects of iontophoretic application of the 5-HT 1A agonist 8-OH-DPAT on auditory responses were compared with the characteristic frequencies (CFs), recording depths, and control first-spike latencies of the same group of IC neurons. The 8-OH-DPAT-evoked change in response significantly correlated with first-spike latency across the population, so that response depressions were more prevalent in longer-latency neurons. The 8-OH-DPAT-evoked change in response did not correlate with CF or with recording depth. 8-OH-DPAT also altered the temporal characteristics of spike trains in a subset of neurons that fired multiple spikes in response to brief stimuli. For these neurons, activation of the 5-HT 1A receptor suppressed lagging spikes proportionally more than initial spikes. These results suggest that the 5-HT 1A receptor, by affecting the timing of the responses of both individual neurons and the neuron population, shifts the temporal profile of evoked activity within the IC.

On and Off magnetic auditory evoked responses in early infancy: A possible marker of brain immaturity

Objective To follow the development of the auditory evoked on- and off-responses in early infancy. Methods The subjects were healthy infants, studied at conceptional age (CA) 39–66 weeks. Serial auditory evoked responses (AERs) were recorded in 17 subjects in response to tones of frequency 1.5 kHz and duration 1.0 s in order to follow the development of the AERs. Two small substudies were performed to examine off-responses evoked by tones of varying duration. The first used 0.2, 0.3, 0.4, and 0.5 s tones; the second used 0.5, 1.0, and 2.0 s tones. Results For the 1.0 s tones, the on- and off-responses consisted of three components: P250, P400, and N750m. The on- and off-responses had similar amplitude, in contrast to adult AERs in which the on-responses are typically much larger. Prior to about CA 47 weeks, the on-responses were actually smaller on average than the off-responses, and in infants born prior to CA 38 weeks the AERs were dominated by the off-response. Off-responses were seen for tones as brief as 0.2 s; however, the P400m component was often absent in the off-responses for tone durations ⩽0.5 s. An interaction was observed in which the N750m-On component was strongly suppressed when it overlapped the P250m-Off. Conclusions Off-responses are much more prominent in infant than in adult AERs, especially in pre-term infants and at early CAs. On- and off-responses also exhibit more complex behavior in infants than in adult; the individual components can interact and behave independently. Significance Measurement of auditory off-responses can improve the assessment of infant neurodevelopment, potentially providing a marker of brain immaturity.

Pure word deafness due to left subcortical lesion: Neurophysiological studies of two patients

Objective This study investigated the auditory processing in two patients with pure word deafness (PWD) using neurophysiological experimental methods. Methods We recorded the auditory brainstem response (ABR), the middle latency auditory-evoked response (MLR) and the auditory-evoked event-related potentials (ERPs) in two patients with PWD after subcortical hemorrhage in the left temporal lobe. Results Both patients showed normal response in ABR and abnormality in MLR. The latency of P300 evoked by right-ear stimulation was 51 ms longer in one patient and 26 ms longer in the other patient than that evoked by left-ear stimulation. Conclusions Our results suggested that the prolongation of P300 latency could be caused by the deterioration of auditory stimulus processing and supported the hypothesis that the defect in auditory temporal resolution was an important factor in the development of PWD. Significance This study demonstrated that recordings of ERP with auditory-evoked response such as ABR and MLR are useful to elucidate the deterioration of auditory stimulus processing in patients with PWD.

Refractory effects on auditory-evoked responses in children with reading disorders

The current study investigated neural refractory effects in children (8-12 years) with reading disorders and a control group. Cortical responses (P1 and N250) to the sound /da / were measured at interstimulus intervals of 538, 1072 and 2152 ms. As expected, owing to slow neural recovery periods, both groups showed longer cortical response latencies at the shortest interstimulus interval of 538 ms. N250 showed a slower neural refractory period at the short interstimulus interval (538 ms) for children with reading disorders than the control group, however. Only control group children showed interhemispheric differences for the N250 peak. No group differences were evident for P1. The results suggest that children with reading disorders have different and slower underlying neural responses than typically developing children.

Inhalational Exposure to Carbonyl Sulfide Produces Altered Brainstem Auditory and Somatosensory-Evoked Potentials in Fischer 344N Rats

Carbonyl sulfide (COS), a chemical listed by the original Clean Air Act, was tested for neurotoxicity by a National Institute of Environmental Health Sciences/National Toxicology Program and U.S. Environmental Protection Agency collaborative investigation. Previous studies demonstrated that COS produced cortical and brainstem lesions and altered auditory neurophysiological responses to click stimuli. This paper reports the results of expanded neurophysiological examinations that were an integral part of the previously published experiments (Morgan et al., 2004, Toxicol. Appl. Pharmacol. 200, 131-145; Sills et al., 2004, Toxicol. Pathol. 32, 1-10). Fisher 334N rats were exposed to 0, 200, 300, or 400 ppm COS for 6 h/day, 5 days/week for 12 weeks, or to 0, 300, or 400 ppm COS for 2 weeks using whole-body inhalation chambers. After treatment, the animals were studied using neurophysiological tests to examine: peripheral nerve function, somatosensory-evoked potentials (SEPs) (tail/hindlimb and facial cortical regions), brainstem auditory-evoked responses (BAERs), and visual flash-evoked potentials (2-week study). Additionally, the animals exposed for 2 weeks were examined using a functional observational battery (FOB) and response modification audiometry (RMA). Peripheral nerve function was not altered for any exposure scenario. Likewise, amplitudes of SEPs recorded from the cerebellum were not altered by treatment with COS. In contrast, amplitudes and latencies of SEPs recorded from cortical areas were altered after 12-week exposure to 400 ppm COS. The SEP waveforms were changed to a greater extent after forelimb stimulation than tail stimulation in the 2-week study. The most consistent findings were decreased amplitudes of BAER peaks associated with brainstem regions after exposure to 400 ppm COS. Additional BAER peaks were affected after 12 weeks, compared to 2 weeks of treatment, indicating that additional regions of the brainstem were damaged with longer exposures. The changes in BAERs were observed in the absence of altered auditory responsiveness in FOB or RMA. This series of experiments demonstrates that COS produces changes in brainstem auditory and cortical somatosensory neurophysiological responses that correlate with previously described histopathological damage.

Hypothyroid‐Associated Central Vestibular Disease in 10 Dogs: 1999–2005

Background:With the exception of myxedema coma, central nervous system signs are rare in hypothyroid dogs.Hypothesis:Central vestibular dysfunction is a possible and reversible manifestation of hypothyroidism.Animals:Medical records of dogs with vestibular dysfunction and hypothyroidism were reviewed. Of 113 records identified, 10 dogs with at least 2 concurrent clinical neurologic abnormalities localizable to the central vestibular system were included.Methods:Retrospective, descriptive study.Results:Median age at diagnosis was 7 years (range, 5–10 years). All dogs were referred for progressive neurologic disease. Lesions were localized to the myelencephalic region in 5 dogs and to the vestibulocerebellum in 5 dogs. Two dogs had evidence of multifocal intracranial disease. Non‐neurologic physical abnormalities suggestive of hypothyroidism were absent in 7 of 10 dogs. Hypercholesterolemia was the only consistent clinicopathologic abnormality detected, and was present in 7 of 10 dogs. All dogs had total thyroxine (TT4) and free thyroxine (fT4) concentrations below reference ranges, and 9 of 10 had increased TSH concentrations. Intracranial imaging studies were normal in 5 of 8 dogs, and identified lesions consistent with infarctions in 3 of 8 dogs. Albuminocytologic dissociation was detected in 5 of 6 CSF analyses. Brainstem auditory‐evoked responses disclosed prolonged wave V latencies in 3 of 4 dogs tested. No other causes of central vestibular dysfunction were identified during other diagnostic investigations. The median time from initiation of treatment to clinical improvement was 4 days. Vestibular signs resolved in 9 of 10 dogs within 4 weeks.Conclusions and Clinical Importance: Although the pathogenesis in dogs without evidence of infarction is unknown, central vestibular dysfunction appears to be a rare but reversible neurologic sequelae of hypothyroidism.

Seasonal variation in avian auditory evoked responses to tones: a comparative analysis of Carolina chickadees, tufted titmice, and white-breasted nuthatches

We tested for seasonal plasticity of the peripheral auditory system of three North American members of the Sylvioidea: Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis). We measured three classes of auditory evoked responses (AER) to tone stimuli: sustained receptor/neural responses to pure-tone condensation waveforms, the frequency-following response (FFR), and the earliest peak of the AER to stimulus onset (tone onset response). Seasonal changes were detected in all classes of AERs in chickadees and nuthatches. Seasonal changes in titmice were restricted to the tone onset response. Interestingly, changes detected in chickadees (and to a lesser extent in titmice) were generally in an opposite direction to changes seen in nuthatches, with chickadees exhibiting greater amplitude AER responses in the spring than in winter, and nuthatches exhibiting greater amplitude AER responses in winter than in spring. In addition, the seasonal differences in the sustained responses tended to be broad-band in the chickadees but restricted to a narrower frequency range in nuthatches. In contrast, seasonal differences in the onset response were over a broader frequency range in titmice than in chickadees and nuthatches. We discuss some possible mechanistic and functional explanations for these seasonal changes.

Mid-Latency Auditory-Evoked Responses and Sensory Gating in Focal Epilepsy: A Preliminary Exploration

Mid-Latency Auditory-Evoked Responses and Sensory Gating in Focal Epilepsy: A Preliminary Exploration

Mid-Latency Auditory-Evoked Responses and Sensory Gating in Focal Epilepsy: A Preliminary Exploration

The relationship between epilepsy and psychosis is not well defined. Sensory gating is a possible endophenotype for psychosis, and has not been fully examined in epileptic patients. The authors examined 29 patients with focal epilepsy who were on antiepileptic medications, and 29 age-matched healthy comparison subjects, using a paired-stimulus (S1-S2) paradigm. P50 and N100 amplitudes or gating did not differ between the groups. The P200 was significantly smaller and did not gate as well in epileptic patients. Though alteration of sensory gating can be demonstrated in epileptic patients, it seems to be qualitatively different from alterations reported in association with schizophrenia.

Ototoxicity in rats exposed to ethylbenzene and to two technical xylene vapours for 13 weeks

Male Sprague-Dawley rats were exposed to ethylbenzene (200, 400, 600 and 800 ppm) and to two mixed xylenes (250, 500, 1,000 and 2,000 ppm total compounds) by inhalation, 6 h/day, 6 days/week for 13 weeks and sacrificed for morphological investigation 8 weeks after the end of exposure. Brainstem auditory-evoked responses were used to determine auditory thresholds at different frequencies. Ethylbenzene produced moderate to severe ototoxicity in rats exposed to the four concentrations studied. Increased thresholds were observed at 2, 4, 8 and 16 kHz in rats exposed to 400, 600 and 800 ppm ethylbenzene. Moderate to severe losses of outer hair cells of the organ of Corti occurred in animals exposed to the four concentrations studied. Exposure to both mixed xylenes produced ototoxicity characterized by increased auditory thresholds and losses of outer hair cells. Ototoxicity potentiation caused by ethylbenzene was observed. Depending on the mixed xylene studied and the area of the concentration-response curves taken into account, the concentrations of ethylbenzene in mixed xylenes necessary to cause a given ototoxicity were 1.7-2.8 times less than those of pure ethylbenzene. Given the high ototoxicity of ethylbenzene, the safety margin of less or equal to two (LOAEL/TWA) might be too small to protect workers from the potential risk of ototoxicity. Moreover, the enhanced ototoxicity of ethylbenzene and para-xylene observed in mixed xylenes should encourage the production of mixed xylenes with the lowest possible concentrations of ethylbenzene and para-xylene.

Magnetoencephalography (MEG) determined temporal modulation of visual and auditory sensory processing in the context of classical conditioning to faces

Using magnetoencephalography (MEG), we determined the time course of sensory-evoked modulations during differential aversive conditioning to faces, with an aversive noise event (UCS). Conditioning was associated with the development of a differential event-related waveform peaking at approximately 150 ms. Source analysis indicated the localization of this modulation to ventral occipital regions. In the auditory domain, a modulation of auditory-evoked responses to a probe sound was evident in a late component emerging at approximately 180 ms over sensors in fronto-temporal regions. The findings indicate the time course in processing sensory stimuli can be altered on the basis of their acquired value.

Development of MEG sleep patterns and magnetic auditory evoked responses during early infancy

Objective To follow the development of MEG sleep patterns and auditory evoked responses (AERs) during the first six months of life. Methods The subjects were 18 neonates, born at conceptional age (CA) 36–42 weeks, following uncomplicated pregnancies. During each session, several 10-min MEG recordings were acquired in the presence of auditory stimulation. The recordings were classified into three distinct MEG patterns—low amplitude irregular; high-amplitude slow; and mixed—based largely on MEG amplitude and frequency. Averaged AERs were computed for the entire recording and for each MEG pattern within the recording. The results were based on analysis of 61 recording sessions of the 10 subjects who yielded three or more sessions of usable data. Results Developmental changes in the MEG sleep patterns were most pronounced at the earliest ages. By CA 48 weeks the patterns had progressed to a more mature form, characterized by the prevalence of delta wave sleep, absence of discontinuity, and development of spindling and higher amplitude delta rhythms. In contrast to the MEG patterns, the AERs did not change markedly during the first 8 weeks (CA 40–48 weeks) and showed a simple morphology, consisting of a prominent deflection at 250 ms (P250m) and a more diffuse one at around 750 ms (N750m). During the period CA 48–54 weeks, however, a relatively abrupt transition occurred to a more complex morphology, characterized by a double peak with peak latencies 150 ms (P150m) and 350 ms (P350m). Beyond this period the AERs continued to evolve, showing biphasic complexes and the emergence of late components arising from outside the auditory cortex. Conclusions Over the age range of this study the MEG sleep patterns and AER developed in succession, rather than concurrently; i.e. development of the sleep patterns was most rapid during the first 8 weeks (CA 40–48 weeks) while major development of the AERs commenced after this time. Significance This finding suggests that the brain must achieve a certain level of overall maturity, reflected in the character of the MEG sleep patterns at CA 48 weeks, before the cortex enters a phase of significant functional development, reflected in the more rapid evolution of the AER after CA 48 weeks. The results of this study affirm the efficacy of MEG for spatiotemporal characterization of neonatal brain activity.

Hypothyroid-Associated Central Vestibular Disease in 10 Dogs: 1999–2005

With the exception of myxedema coma, central nervous system signs are rare in hypothyroid dogs. Central vestibular dysfunction is a possible and reversible manifestation of hypothyroidism. Medical records of dogs with vestibular dysfunction and hypothyroidism were reviewed. Of 113 records identified, 10 dogs with at least 2 concurrent clinical neurologic abnormalities localizable to the central vestibular system were included. Retrospective, descriptive study. Median age at diagnosis was 7 years (range, 5-10 years). All dogs were referred for progressive neurologic disease. Lesions were localized to the myelencephalic region in 5 dogs and to the vestibulocerebellum in 5 dogs. Two dogs had evidence of multifocal intracranial disease. Non-neurologic physical abnormalities suggestive of hypothyroidism were absent in 7 of 10 dogs. Hypercholesterolemia was the only consistent clinicopathologic abnormality detected, and was present in 7 of 10 dogs. All dogs had total thyroxine (TT4) and free thyroxine (fT4) concentrations below reference ranges, and 9 of 10 had increased TSH concentrations. Intracranial imaging studies were normal in 5 of 8 dogs, and identified lesions consistent with infarctions in 3 of 8 dogs. Albuminocytologic dissociation was detected in 5 of 6 CSF analyses. Brainstem auditory-evoked responses disclosed prolonged wave V latencies in 3 of 4 dogs tested. No other causes of central vestibular dysfunction were identified during other diagnostic investigations. The median time from initiation of treatment to clinical improvement was 4 days. Vestibular signs resolved in 9 of 10 dogs within 4 weeks. Although the pathogenesis in dogs without evidence of infarction is unknown, central vestibular dysfunction appears to be a rare but reversible neurologic sequelae of hypothyroidism.

Effects of Attention on Neuroelectric Correlates of Auditory Stream Segregation

A general assumption underlying auditory scene analysis is that the initial grouping of acoustic elements is independent of attention. The effects of attention on auditory stream segregation were investigated by recording event-related potentials (ERPs) while participants either attended to sound stimuli and indicated whether they heard one or two streams or watched a muted movie. The stimuli were pure-tone ABA--patterns that repeated for 10.8 sec with a stimulus onset asynchrony between A and B tones of 100 msec in which the A tone was fixed at 500 Hz, the B tone could be 500, 625, 750, or 1000 Hz, and--was a silence. In both listening conditions, an enhancement of the auditory-evoked response (P1-N1-P2 and N1c) to the B tone varied with Deltaf and correlated with perception of streaming. The ERP from 150 to 250 msec after the beginning of the repeating ABA- patterns became more positive during the course of the trial and was diminished when participants ignored the tones, consistent with behavioral studies indicating that streaming takes several seconds to build up. The N1c enhancement and the buildup over time were larger at right than left temporal electrodes, suggesting a right-hemisphere dominance for stream segregation. Sources in Heschl's gyrus accounted for the ERP modulations related to Deltaf-based segregation and buildup. These findings provide evidence for two cortical mechanisms of streaming: automatic segregation of sounds and attention-dependent buildup process that integrates successive tones within streams over several seconds.

Brainstem auditory-evoked response in dogs

5-12 Although such an approach may be used to obtain a psychoacoustic audiogram in which the frequency of the sound is plotted against the minimum intensity required to elicit a behavioral response, results are influenced by the dog’s mental state, rate of adaptation to the sound stimulus, and sensitivity to visual and vibratory stimuli. 5-12 As a result, proper training of both the dog and the human tester is required before reliable results can be obtained. These factors make the use of behavioral responses a poor choice for inexperienced testers, young puppies, and clinical patients. 7

Modulation of P2 auditory-evoked responses by the spectral complexity of musical sounds

We investigated whether N1 and P2 auditory-evoked responses are modulated by the spectral complexity of musical sounds in pianists and non-musicians. Study participants were presented with three variants of a C4 piano tone equated for temporal envelope but differing in the number of harmonics contained in the stimulus. A fourth tone was a pure tone matched to the fundamental frequency of the piano tones. A simultaneous electroencephalographic/magnetoencephalographic recording was made. P2 amplitude was larger in musicians and increased with spectral complexity preferentially in this group, but N1 did not. The results suggest that P2 reflects the specific features of acoustic stimuli experienced during musical practice and point to functional differences in P2 and N1 that relate to their underlying mechanisms.

Brainstem Auditory-Evoked Potential Assessment of Auditory Function and Congenital Deafness in Llamas (Lama glama) and Alpacas (L pacos)

Auditory function of llamas and alpacas was assessed objectively by means of brainstem auditory-evoked response audiometry (BAER) to establish the normal hearing range and to test the hypothesis of a correlation between blue eyes, white coat, and deafness. Sixty-three camelids were available for the study. Thirteen animals had blue irides; 1 animal had 1 blue and 1 pigmented iris. Wave latencies, amplitudes, and interpeak latencies were measured under general anesthetic. Click stimuli (dB [HL]) were delivered by an insert earphone. Four to five positive peaks could be detected; waves I, II, and V were reproducible; wave II appeared infrequently; and wave IV generally merged with wave V to form a complex. Peak latencies decreased and peak amplitudes increased as stimulus intensity increased. A hearing threshold level of 10-20 dB (HL) was proposed as the normal range in llamas and alpacas. None of the animals with pigmentation of coat and iris showed any degree of hearing impairment. Seven of the 10 blue-eyed, pure-white animals were bilaterally deaf and one of them was unilaterally deaf. However, 2 blue-eyed, white animals exhibited normal hearing ability. Three blue-eyed animals with pigmented coat did not show any hearing impairment. All white animals with normal iris pigmentation had normal auditory function; so did the 1 animal with 1 normal and 1 blue iris. The high frequency (78%) of bilaterally deaf animals with pure white coat and blue iris pigmentation supports the hypothesis of a correlation between pigmentation anomalies and congenital deafness in llamas and alpacas.