Effects of bilateral lesions of auditory cortex in mice on the acoustic startle response

The acoustic startle response (ASR) was used to investigate the effects of auditory cortical lesions on a brain stem-mediated auditory behavior. The ASRs were obtained longitudinally from young adult C57BL/6J mice before bilateral ablation of auditory cortex, 1 day after ablation, and 1 month later. Control mice received lesions of nonauditory cortex. For some mice, averaged brain stem-evoked responses (ABR) were obtained, and these indicated no effects of lesions on auditory sensitivity. One month after surgery, mice with auditory cortex ablations were statistically indistinguishable from controls on all suprathreshold measures of ASR. However, 1 day after ablation of auditory cortex, experimental animals (but not controls) exhibited a change in ASR amplitude (but not threshold or latency). When a noise burst of 80 dB SPL was used to elicit the ASR, the amplitude was diminished, but with a 110 dB stimulus, amplitude was enhanced. The findings can be interpreted in one of two ways: temporary interference with modulation of the ASR normally performed by auditory cortex; or a general effect of auditory cortex ablation on brain stem auditory circuits not specific to the ASR. In any event, if auditory cortex plays a modulatory role with regard to the ASR, it is apparently nonessential and/or readily compensated for after ablation.     

Ontogeny of the acoustic startle response and sensitization to background noise in the rat.

The purpose of this study was to characterize the ontogeny of the acoustic startle response (ASR) and response sensitization to background noise in preweanling rats. Animals were tested daily from 11 to 21 days of age using one of four sets of background white noise levels [45–80 dB(A)]. With constant low-level (45 dB, SPL) background noise, response latency decreased steadily with age, whereas both response incidence and amplitude increased nonmonotonically with age. Two approaches were used to examine the ontogeny of sensitization to background noise: The first compared the ASR of animals tested at 75 dB background noise with ones tested at 45 dB; the second compared the ASR of animals tested at three background levels (30 dB range) within the test session. Sensitization was not evident before 15–26 days of age. By comparing these results with the results from naive animals, it was found that daily test experience does not alter ASR amplitude, latency, incidence, or the development of sensitization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thyroxine affects physiological and morphological development of the ear

The onset and development of distortion product otoacoustic emissions (DPE) representing cochlear amplifier activity were studied in neonatal hyperthyroid (n = 10) and control (n = 10) rat pups. These were compared to the onset and development of auditory nerve-brainstem evoked responses (ABR) representing overall cochlear function, and to morphological development of the ear. DPEs were recorded at an earlier postnatal age to high (8 kHz) frequencies and progressed to lower (3 kHz) frequencies with age. ABRs to high-intensity clicks were recorded at least 2 days before DPEs, although DPE onset at 8 kHz preceded adult-like ABR thresholds. Both ABR and DPEs appeared earlier in the hyperthyroid rats. Histological evidence showed earlier morphological development of the ear in these animals. ABR thresholds and DPE amplitudes matured at a slower rate in the experimental group despite their earlier onset. There was no difference in ABR and DPE thresholds between adult hyperthyroid and control rats. However, in the experimental group, DPEs had smaller amplitudes to high (70 dB SPL) and to low (50 dB SPL) stimulus intensities at low frequencies. Hence, despite thyroxine-injected rat pups having earlier onset of auditory structure and function (lower ABR thresholds and earlier functioning active cochlear amplifier), it appeared that neonatal hyperthyroidism affected the later state of the cochlea, such that DPEs, especially to low-frequency stimuli, were depressed during and after maturation.     

Developmental exposure to Aroclor 1254 produces low-frequency alterations in adult rat brainstem auditory evoked responses

Developmental exposure of Long-Evans rats to 0, 1, 4, or 8 mg/kg/day Aroclor 1254 (A1254) from Gestational Day 6 through Postnatal Day 21 produces an elevated behavioral threshold for a 1-kHz tone. Brainstem auditory evoked responses (BAERs) were assessed in a subset of these animals (about 1 year old) using filtered clicks at 1 (65 and 80 dB SPL), 4 (60 and 80 dB SPL), 16 (40 and 80 dB SPL), and 32 (40 and 80 dB SPL) kHz. Aroclor 1254 decreased BAER amplitudes at 1 and 4 kHz, but not at 16 or 32 kHz. A dose-related decrease in the baseline-to-peak P1A amplitude was observed for the 1-kHz (80-dB) stimulus. Doses of 1, 4, or 8 mg/kg/day A1254 decreased the peak-to-peak amplitude of both P1AN1 and P1BN1 for a 1-kHz (80-dB) stimulus. Doses of 4 and 8 mg/kg/day A1254 decreased the peak-to-peak amplitude of N1P2 and P2N2 for a 4-kHz (60-dB) or 1-kHz (80-dB) stimulus. At 8 mg/kg/day, A1254 also increased the latency of peak P4 at 1 kHz (65 dB). The decreases in peak P1A amplitudes are consistent with a dysfunction of the cochlea and/or auditory nerve. Together, the data confirm that developmental exposure of rats to A1254 produces a permanent low- to mid-frequency auditory dysfunction and suggest a cochlear and/or auditory nerve site of action.     

Circadian modulation in the rat acoustic startle circuit.

The acoustic startle reflex (ASR) in rats exhibits robust circadian modulation, with ASR amplitudes greater during subjective night. To identify the location of this modulation, startle reactions were evoked either acoustically or electrically via electrodes implanted in the primary ASR circuit. Startle amplitudes were compared at different times in the circadian cycle. In constant environmental conditions, startle amplitudes were greater in subjective night for acoustically evolved and for electrically evoked reactions from the ventral lateral lemniscus and medial longitudinal fasciculus. The results show that at least 1 site of circadian modulation must occur at some point in the circuit after the last brainstem synapse in the caudal pontine reticular formation, at the level of spinal interneurons or motoneurons or at the neuromuscular junction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of click intensity and frequency on the brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 20 common marmosets (Callithrix jacchus) to investigate the effects of click frequency up to 99 kHz, in consideration of the higher hearing range of the marmoset, and intensity on wave forms and peak latencies. According to the results of BAEP recordings at frequencies of 4, 32, and 99 kHz, the number of components recorded was affected by the stimulus intensity and the clicks at an intensity of 80 dB peak equivalent sound pressure level (pe SPL) had the maximum number of clear components. Therefore, it was indicated that click stimulations at an intensity of 80 dB pe SPL over a broad range of frequencies appears to be useful for recording the maximum number of components in marmosets and may increase the information obtainable from BAEPs. BAEP latencies were prolonged as the stimulus intensity decreased from 100 to 50 dB pe SPL. The effects of stimulus frequency on the wave latencies and amplitudes in response to 80 dB pe SPL at frequencies between 0.5 and 99 kHz revealed various changes: the amplitude of wave I increased at 16 and 32 kHz, but that of waves III and V increased at 4-8 and 64-99 kHz. These increases in amplitudes of the waves may correlate with higher synchronous activity of the peripheral or central auditory pathways.     

Cytochemical and biochemical studies on adenylate cyclase activity in preneoplastic and neoplastic liver tissue and cultured liver cells

OBJECTIVE: To assess the accuracy of: 1) distortion product otoacoustic emission (DPOAE) measures for the identification of frequencies at which auditory sensitivity is normal or near normal; and 2) click and nonmasked tone burst-evoked auditory brain stem response (ABR) thresholds for behavioral threshold estimation for children with sensorineural hearing loss characterized by islands of normal sensitivity. DESIGN: DPOAEs and ABRs were recorded from five hearing-impaired and eight normal-hearing pediatric ears. The accuracy with which DPOAEs permitted identification of frequencies at which elevated hearing thresholds were present was examined. ABR and pure-tone threshold differences for the impaired ears were calculated. RESULTS: For three of the five hearing-impaired ears, significant impairments would have been missed based on click-evoked ABR thresholds. One of those hearing-impaired ears provided an essentially normal 500 Hz tone burst-evoked ABR threshold as well. Four of the hearing-impaired ears provided a 500 Hz tone burst-evoked ABR threshold within 10 dB of the respective pure-tone threshold. However, click-evoked ABR and 500 Hz tone burst-evoked ABR threshold data did not adequately delineate the hearing loss configuration for hearing aid frequency response selection. DPOAEs were present at three out of four frequencies from 1000 to 4000 Hz at which sensitivity was normal or near normal (< or =25 dB HL) and absent at 10 out of 11 frequencies at which sensitivity was impaired. The use of DPOAEs to identify frequencies at which sensitivity was normal and the use of tone burst ABR thresholds at frequencies where DPOAEs were absent provided a better estimate of these pure-tone audiograms than was provided by click-evoked and 500 Hz tone burst-evoked ABR thresholds.     

Acoustic startle response in young and aging C57BL/6J and CBA/J mice.

C57 mice demonstrate progressive age-related hearing loss during the 1st yr, whereas CBA mice lose little sensitivity through 18 mo of age. The acoustic startle response (ASR) was measured to determine behavioral correlates of aging with and without presbycusis. Stimuli were tone pips with frequencies of 4–24 kHz at intensities of 70–200 dB SPL. ASR thresholds increased with age, and startle amplitudes became smaller. Changes in startle parameters were more pronounced in C57 mice, with middle to high frequencies severely affected. Startle latencies at and above ASR threshold increased with age in C57 mice. CBA data indicate that aging has little effect on ASR parameters; the C57 data show that hearing loss is a cogent factor. ASR parameters of C57 mice are altered to a greater extent than expected, on the basis of the elevations of absolute sensory thresholds, particularly for middle frequencies. Both peripheral and central mechanisms may account for the discrepancy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral Limits of Auditory Temporal Resolution in the Rat: Amplitude Modulation and Duration Discrimination.

Thresholds for detecting the presence of amplitude modulation in a noise carrier were determined for rats using conditioned avoidance procedures. There was a progressive increase in threshold with modulation rates between 5 Hz and 2 kHz. Further tests were conducted to determine difference thresholds for detecting an increase in modulation rate for standard rates of 10, 50, and 100 Hz. The size of the difference threshold increased progressively as the standard rate increased. In addition, thresholds for detecting an increase in the duration of a noise burst were determined for various standard durations. The difference thresholds were constant for values between 10 and 50 ms but increased progressively, with standard durations between 0.1 and 1.0 s. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned brain-stimulation reward attenuates the acoustic startle reflex in rats.

The acoustic startle reflex (ASR) in rats is attenuated by a light paired with food or, in humans, by "pleasant" pictures. Rats were trained to barpress for lateral hypothalamus (LH) stimulation. ASR amplitudes were then measured at 4 intensities, with or without a light. Control rats that did not receive brain-stimulation reward (BSR) showed initially lower ASR amplitudes than did rats exposed to BSR, but both groups responded similarly with or without light. Next, experimental rats were given BSR in the presence of light but not in its absence. After conditioning, ASR amplitudes were reduced, and ASR thresholds were raised by a mean of 2.6 dB in the light but remained at preconditioning levels without light. No such change was found for control rats or rats with placements outside the LH. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

ART restorations and glass ionomer sealants in Zimbabwe: survival after 3 years

Preliminary investigations have been made in normally hearing alert adults to establish whether the 40 Hz modulation-following response (MFR) can be used to predict 400 Hz uncomfortable loudness levels (ULLs). The MFR stimulus was a 400 Hz carrier, amplitude- and frequency-modulated by a 40 Hz sine function. Subjective ULLs were obtained using standard procedures. Objective ULLs were obtained from MFR parameter intensity functions using rms amplitude, phase angle and magnitude-squared coherence (40 Hz components). The best predictions of the subjective ULL were made using objective ULLs calculated from the gradients of linear best-fit lines for individual phase-intensity functions (80 per cent predicted within 10 dB of the subjective ULL; maximum deviation=16 dB). Poorest predictions were based on inter-subject average rms amplitude-intensity functions, where as few as 14 per cent were within 10 dB of the subjective value. The best predictions were considered sufficiently accurate to warrant further investigation using a variety of modulation and carrier frequencies in different age groups and with varying degrees of hearing loss.     

Quantitative analysis of the plain radiographic appearance of unicameral bone cysts

The reliability and frequency specificity of the 80-Hz amplitude-modulation-following response (80-Hz AMFR) during sleep detected by phase coherence as a measure of the hearing threshold was evaluated in 169 affected ears of 125 children with hearing impairment. The 80-Hz AMFR at a carrier frequency of 1000 Hz was monitored in all 169 ears and the auditory brainstem response (ABR) elicited by 1000-Hz tone pips was evaluated in 93 ears. Both responses were examined during sleep, and the thresholds were compared with the behavioral hearing threshold, which was determined by standard pure-tone audiometry or play audiometry. In 24 ears of 22 children with various patterns of audiogram, the 80-Hz AMFR was examined at different carrier frequencies, and the threshold pattern was compared with the pure-tone audiogram to investigate the frequency specificity of 80-Hz AMFR. The mean and standard deviation of the difference between the 80-Hz AMFR at a carrier frequency of 1000 Hz and pure-tone thresholds of 1000 Hz was 3.8 and 12.9 dB, and that between the ABR and pure-tone thresholds was 6.8 and 14.1 dB, respectively. The threshold patterns of 80-Hz AMFR clearly followed the corresponding audiogram patterns in all types of hearing impairment. The measurement of 80-Hz AMFR thus appears to be accurate in hearing assessment and to have good frequency specificity in children during sleep.     

Low-frequency acoustic modulations generated by the high-frequency portion of the cochlea, noninvasively recorded from the scalp of mice (Mus musculus).

Vocalizations often contain low-frequency modulations of the envelope of a high-frequency sound. The high-frequency portion of the cochlear nerve of mice (Mus musculus) generates a robust phase-locked response to these low-frequency modulations, and it can be easily recorded from the surface of the scalp. The cochlea is most sensitive to envelope modulation frequencies of approximately 500 to 2000 Hz. These responses have detection thresholds that are approximately 10 dB more sensitive than auditory brainstem responses, and they are very sharply tuned. These measurements may provide a nontraumatic means of repeatedly assessing cochlear functions involved in sound localization and perception of vocalizations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Frequency tuning and spontaneous activity in the auditory nerve and cochlear nucleus magnocellularis of the barn owl Tyto alba

Single-unit recordings were obtained from the brain stem of the barn owl at the level of entrance of the auditory nerve. Auditory nerve and nucleus magnocellularis units were distinguished by physiological criteria, with the use of the response latency to clicks, the spontaneous discharge rate, and the pattern of characteristic frequencies encountered along an electrode track. The response latency to click stimulation decreased in a logarithmic fashion with increasing characteristic frequency for both auditory nerve and nucleus magnocellularis units. The average difference between these populations was 0.4-0.55 ms. The average most sensitive thresholds were approximately 0 dB SPL and varied little between 0.5 and 9 kHz. Frequency-threshold curves showed the simple V shape that is typical for birds, with no indication of a low-frequency tail. Frequency selectivity increased in a gradual, power-law fashion with increasing characteristic frequency. There was no reflection of the unusual and greatly expanded mapping of higher frequencies on the basilar papilla of the owl. This observation is contrary to the equal-distance hypothesis that relates frequency selectivity to the spatial representation in the cochlea. On the basis of spontaneous rates and/or sensitivity there was no evidence for distinct subpopulations of auditory nerve fibers, such as the well-known type I afferent response classes in mammals. On the whole, barn owl auditory nerve physiology conformed entirely to the typical patterns seen in other bird species. The only exception was a remarkably small spread of thresholds at any one frequency, this being only 10-15 dB in individual owls. Average spontaneous rate was 72.2 spikes/s in the auditory nerve and 219.4 spikes/s for nucleus magnocellularis. This large difference, together with the known properties of endbulb-of-Held synapses, suggests a convergence of approximately 2-4 auditory nerve fibers onto one nucleus magnocellularis neuron. Some auditory nerve fibers as well as nucleus magnocellularis units showed a quasiperiodic spontaneous discharge with preferred intervals in the time-interval histogram. This phenomenon was observed at frequencies as high as 4.7 kHz.     

Low-frequency suppression of auditory nerve responses to characteristic frequency tones

The effects of low-frequency (50, 100, 200 and 400 Hz) 'suppressor' tones on responses to moderate-level characteristic frequency (CF) tones were measured in chinchilla auditory nerve fibers. Two-tone interactions were evident at suppressor intensities of 70-100 dB SPL. In this range, the average response rate decreased as a function of increasing suppressor level and the instantaneous response rate was modulated periodically. At suppression threshold, the phase of suppression typically coincided with basilar membrane displacement toward scala tympani, regardless of CF. At higher suppressor levels, two suppression maxima coexisted, synchronous with peak basilar membrane displacement toward scala tympani and scala vestibuli. Modulation and rate-suppression thresholds did not vary as a function of spontaneous activity and were only minimally correlated with fiber sensitivity. Except for fibers with CF < 1 kHz, modulation and rate-suppression thresholds were lower than rate and phase-locking thresholds for the suppressor tones presented alone. In the case of high-CF fibers with low spontaneous activity, excitation thresholds could exceed suppression thresholds by more than 30 dB. The strength of modulation decreased systematically with increasing suppressor frequency. For a given suppressor frequency, modulation was strongest in high-CF fibers and weakest in low-CF fibers. The present findings strongly support the notion that low-frequency suppression in auditory nerve fibers largely reflects an underlying basilar membrane phenomenon closely related to compressive non-linearity.     

Sex and strain differences of acoustic startle reaction development in adolescent albino Wistar and hooded rats

Acoustic startle responses (ASR) were studied in 12 young Wistar albino and in 15 hooded rats of both genders. The six week old animals were first exposed to a 6.9 kHz tone pair of 2 ms pulses of 120 db intensity with the inter-stimulus interval (ISI) between 2 and 11 ms. ASR amplitudes and latencies as a function of the ISI, animal strain and gender were recorded and analyzed for ten consecutive weeks. No differences in the ASR amplitude between Wistar and hooded rats were found. ASR amplitude increased during the experimental period and followed body weight increase. Significant differences were also observed between male and female rats in their startle responses to acoustic stimuli. Generally, male subjects responded with a greater ASR amplitude than females, and the changes may be attributed to the difference in neuromuscular development between genders. This experiment sets a background for further developmental studies.     

Cellular mechanisms of hypoxia-induced contraction in human and rat pulmonary arteries

Two experiments examined the effects of age, genetic strain, and nicotine on acoustic startle response (ASR) amplitude and prepulse inhibition (PPI) in rats. ASR amplitude measures reactivity to external stimulation, and PPI is used as an index of sensory gating related to attention. Both ASR amplitude and PPI have been previously reported to be increased by nicotine in adult rats. Experiment 1 examined effects of chronically administered nicotine and saline on ASR and PPI in Wistar, Long-Evans, and Sprague-Dawley rats (40 days of age). Experiment 2 examined the effects of chronically administered nicotine and saline in Sprague-Dawley rats of two age groups: 40 and 70 days of age at the beginning of the study. ASR amplitude differed significantly across strains with the values for Wistar > Sprague-Dawley > Long-Evans, and there were no differences in percent of PPI among the three strains. In addition, results of Experiment 2 indicated that older rats had significantly greater ASR amplitudes and PPI than younger rats. Consistent with previous reports, nicotine increased ASR and PPI in the older rats; however, there were no significant differences in the younger rats. Therefore, age and genetic strain are important variables in the analysis of nicotine's effects on startle behaviors in rats.     

Auditory steady-state response to sinusoidally amplitude-modulated tones. Second report: investigation of response in the sleeping state

The auditory steady state response (SSR) elicited by a sinusoidally amplitude-modulated (SAM) tone may be an important technique in objective audiometry, which provides frequency-specific information. This response is affected the state of arousal of the subject. An effect of sleep on the amplitude of this response has been observed by a number of previous investigators. Since young children must usually be sedated to carry out evoked potential testing, the effects of sleep on this response are a crucial factor limiting clinical applicability. The basic characteristics of SSR elicited by a 500 Hz SAM tone were studied in 21 adults with normal hearing during sleep. The responses while sleeping were compared with the responses in the awake state. The responses to 2048 stimuli were averaged with the analysis time set at 102.4 ms, and responses were judged by passing the waveforms through a 20-100 Hz digital filter. The same technique was performed in 25 infants (2 months-2 years 9 months) evaluated as having normal hearing. The results obtained are summarized as follows: The amplitude of the response while sleeping was approximately half the amplitude in the awake state. Responses with a modulation frequency of 70Hz, however, showed a persistent decrease in 71.0%, suggesting a trend different from that seen at a modulation frequency of less than 70Hz. The effect of modulation frequency on response amplitude was almost the same for the sleeping state and the awake state. Even during sleep, the response amplitude was maximal at modulation frequencies of 20, 30 and 40Hz, and there was no significant difference between the values at 20Hz -40Hz. The latency of the response was measured by the Diamond method, and the results showed that latency is significantly prolonged while sleeping (p < 0.01). The response threshold at the 500Hz SAM tone (modulation rate 40Hz, modulation depth 90%) was 8.5dBnHL when awake and 13.9dBnHL during sleep. The rise in threshold as a result of sleep was no more than about 5dB. In infants, the response amplitude at a modulation frequency of 20Hz was maximal, and amplitude at the 40Hz was significantly smaller (p < 0.01). Latency measured by the Diamond method in infants was 12.8ms. Thus, a difference from the response in adults was confirmed. Comparisons were made between the responses of infants under 1 year of age and infants over 1 year of age to confirm changes in response according to age.     

Modulation detection interference in cochlear implant subjects

The aim of this study was to determine whether detection thresholds for amplitude modulated signals on a single electrode were influenced by a masking modulation on a second electrode in cochlear implant users. Data were collected from four post-linguistically deafened subjects using the Cochlear Limited prosthesis. Investigated were the effects of the spatial separation between test and masker electrodes, 0 to 5 electrodes (0 to 3.75 mm), and the amount of masking modulation: 24%, 48%, 72%, and 96% above detection thresholds. Initially, modulation detection thresholds for stimulation on a single electrode without masking modulation were obtained for a set of six electrodes in the middle of the array. Modulation detection thresholds on a fixed test electrode were then obtained with unmodulated and modulated masking on a second electrode, which was one of the six electrodes in the initial study. In both studies, thresholds were measured for modulated pulse duration at the modulation frequencies of 10-200 Hz. In the first study, the shape of the detection thresholds as a function of modulation frequency, the temporal modulation transfer function, generally resembled a low-pass filter for two subjects. For the other two subjects, the functions were relatively flat across modulation frequencies. In the second study, unmodulated masking resulted in a small elevation in detection thresholds across electrodes. Modulation detection interference (MDI), the difference between thresholds for the modulated maskers and the unmodulated masker, was greater for larger amounts of masking modulation than for smaller amounts of masking modulation. For three of the four subjects, MDI was higher for smaller spatial separations between the two electrodes than for larger spatial separations suggesting that a portion of MDI may be due to overlap of neural excitation distributions produced by stimulation on two electrodes in close proximity on the array.     

Effects of auditory cortical lesions on pure-tone sound localization by the albino rat.

Used 2-choice and 3-choice tests to evaluate the effects of bilateral auditory cortical lesions on pure-tone sound localization by 10 male albino rats. Both tests required that Ss approach a distant sound source to obtain water reinforcement. Stimuli were single noise and tone bursts, 65 msec in duration including 20-msec rise and fall times. Tone frequencies were 2, 4, 8, 16, and 32 kHz adjusted to 40 dB (sound pressure level) above the S's absolute threshold. Five Ss were tested in the 2-choice situation following bilateral ablation of auditory cortex. Some reduction in performance was observed relative to normals, but impairments were not severe. Similar results were obtained for 2 brain-damaged Ss tested in the 3-choice situation. Thus, the ability to localize sounds in space remained intact after complete destruction of auditory cortex, and there was no indication of a frequency-dependent deficit. Findings are considered in relation to the more severe deficits observed in other mammals after lesions of the auditory cortex. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)