Prolonged maturation of cochlear function in the barn owl after hatching

Cochlear microphonics (CMs), which represent the electrical activity of hair cells, and compound action potentials (CAPs), which represent the activity of the auditory nerve, were recorded from the round window of the inner ear, in owlets aged between 5 and 97 days posthatching, i.e., from soon after hatching to beyond fledgling. At the earliest ages examined, animals showed very insensitive CM and virtually no CAP responses. Thus, hearing in barn owls develops entirely posthatching and the birds appear to be profoundly deaf well into the second week. Thresholds improved gradually after that and CMs reached their adult sensitivity at 5 weeks posthatching at all frequencies. Compound action potential responses appeared progressively later with increasing frequency. Adult neural sensitivity was achieved about 1 week later than for the CM responses at most frequencies, but took until 9–10 weeks posthatching at the highest frequencies (8–10 kHz). This indicates an apex-to-base maturation sequence of neural sensitivity within the cochlea, with a disproportionately long period to maturity for the most basal regions. Compound action potential amplitudes matured even later, at about 3 months posthatching, at all frequencies. This suggests a prolonged immaturity in the temporal synchrony of spiking in the auditory nerve.     

Multiple specializations in the peripheral auditory system of the CF-FM bat,Pteronotus parnellii

Summary Cochlear microphonic (CM) and evoked neural potentials (N₁) were recorded from the cochlear aqueduct of awakePteronotus parnellii. The CM audiograms obtained with continuous sounds had more or less uniform thresholds except for a sharp threshold notch at about 60 kHz (Fig. 1). When brief tone bursts were presented, the envelopes of the CM responses were always similar to the envelopes of the applied signals except when tone bursts having frequencies at or close to the frequency of the tuned sensitivity notch were presented (i.e., 59–63 kHz). The CM rise-decay times for frequencies around 60kHz were much longer than those of the presented signals (Fig. 2). The prolonged decay times are thought to be due to the ringing of the basilar membrane resulting from a mechanical resonance in the cochlea.The evoked neural potential audiograms (N₁-on and N₁-off responses) differed considerably from the CM audiogram. Of particular importance is the N₁-off audiogram which exhibited very sharp tuning in four frequency regions: 31–33 kHz, 60–63 kHz, 71–73 kHz, and 91–92 kHz (Fig. 5). The frequencies evoking the lowest thresholds of the CM and N₁-off (in the 60 kHz region) were either identical or differed by only 100–400 Hz.The sharp tuning in the 60 kHz region of both the CM and N₁ audiograms could be eliminated by presenting 90–100 dB continuous sounds for one min but only if the signal frequency was equal to the tuned frequency of the CM audiogram (Figs. 8–13). Presenting intense sounds having frequencies above or below the tuned 60kHz region had no effect on the audiogram. The overstimulation procedure had remarkably specific effects on the CM and N₁-off audiograms causing the greatest threshold increases at the 60 kHz tuned frequency and progressively smaller threshold changes on the slopes of the tuned notch.Assuming that the sharp changes of the N₁-off thresholds reflect some important underlying mechanism, the N₁-off audiograms demonstrate multiple specializations in the peripheral auditory system ofPteronotus with the bat possessing at least three and possibly four sharply tuned regions. With regard to mechanism, the tuned notch in the CM audiogram, the curious CM rise-decay times evoked by tone bursts, and the ease with which the 60 kHz sensitivity notch can be eliminated all argue strongly in favor of a mechanical resonance in the cochlea which is responsible for the sharp tuning around 60 kHz. On the other hand, the absence of tuned notches in the 30 kHz and 90 kHz regions of the CM audiogram together with the absence of any discernable ringing of the CM potentials evoked by 30 kHz and 90 kHz tone bursts both argue against a resonance mechanism for the tuning at these harmonically related frequency regions. Finally, the fact that overstimulating the 60 kHz region had no discernable effect on the N₁-off tuning at 30 kHz and 90 kHz demonstrates that the mechanism responsible for the tuned regions at 30 kHz and 90 kHz are independent of the resonance feature of the cochlea at 60 kHz.Abbreviations BF best frequency - CF constant frequency - CM cochlear microphonics - CM-aft after-response of the CM - FM frequency modulated - N ₁ evoked neural potentials We thank Professor Alvin Novick for the generous support provided during the conduct of these experiments. We also thank Professor Gerhard Neuweiler and Dr. Gerd Schuller for their helpful comments and suggestions. Supported by PHS Grant NB7616 11.     

The group delay and suppression pattern of the cochlear microphonic potential recorded at the round window

Background

It is commonly assumed that the cochlear microphonic potential (CM) recorded from the round window (RW) is generated at the cochlear base. Based on this assumption, the low-frequency RW CM has been measured for evaluating the integrity of mechanoelectrical transduction of outer hair cells at the cochlear base and for studying sound propagation inside the cochlea. However, the group delay and the origin of the low-frequency RW CM have not been demonstrated experimentally.

Methodology/Principal Findings

This study quantified the intra-cochlear group delay of the RW CM by measuring RW CM and vibrations at the stapes and basilar membrane in gerbils. At low sound levels, the RW CM showed a significant group delay and a nonlinear growth at frequencies below 2 kHz. However, at high sound levels or at frequencies above 2 kHz, the RW CM magnitude increased proportionally with sound pressure, and the CM phase in respect to the stapes showed no significant group delay. After the local application of tetrodotoxin the RW CM below 2 kHz became linear and showed a negligible group delay. In contrast to RW CM phase, the BM vibration measured at location ∼2.5 mm from the base showed high sensitivity, sharp tuning, and nonlinearity with a frequency-dependent group delay. At low or intermediate sound levels, low-frequency RW CMs were suppressed by an additional tone near the probe-tone frequency while, at high sound levels, they were partially suppressed only at high frequencies.

Conclusions/Significance

We conclude that the group delay of the RW CM provides no temporal information on the wave propagation inside the cochlea, and that significant group delay of low-frequency CMs results from the auditory nerve neurophonic potential. Suppression data demonstrate that the generation site of the low-frequency RW CM shifts from apex to base as the probe-tone level increases.     

Acoustical and neural aspects of hearing in the Australian gleaning bats,Macroderma gigas andNyctophilus gouldi

1. The maximum acoustic gain of the external ear in Macroderma gigas was found to be 25-30 dB between 5-8 kHz and in Nyctophilus gouldi it reached 15-23 dB between 7-22 kHz. Pinna gain reached a peak of 16 dB near 4.5-6 kHz in M. gigas and 12-17 dB between 7-12 kHz in N. gouldi, with average gain of 6-10 dB up to 100 kHz. Pinna gain curves resemble that of a finite conical horn, including resonance. 2. The directional properties of the external ear in both species result from sound diffraction at the pinna face, as it approximates a circular aperture. The frequency dependent movement of the acoustic axis in azimuth and elevation is attributed to the asymmetrical structure of the pinnae. 3. Evoked potentials and neuronal responses were studied in the inferior colliculus. In M. gigas, the neural audiogram has sensitivity peaks at 10-20 kHz and 35-43 kHz, with extremely low thresholds (-18 dB SPL) in the low frequency region. In N. gouldi, the neural audiogram has sensitivity peaks at 8-14 kHz (lowest threshold 5 dB SPL) and 22-45 kHz. Removal of the contralateral pinna causes a frequency dependent loss in neural threshold sensitivity of up to 10-15 dB in both species. 4. The high frequency peak in the audiogram coincides with the sonar energy band in both species, whereas the low frequency region is used for social communication. Highly sensitive low frequency hearing is discussed in relation to hunting in bats by passive listening.     

Electrophysiological responses in guinea pig cochlea to low frequency sound stimuli: distortion of cochlear microphonic (CM) wave form

The present experiment investigated whether or not auditory responses of the middle and/or inner ear in guinea pigs to low frequency sound stimuli [ 60 Hz-2 kHz at 90-120 dB(SPL) ] exhibited the harmonic distortion phenomenon resulting from cochlear microphonics (CM). Measurement of CM leading in turn I by the differential electrode recording method involved measurement of 50 microV isopotential responses, output voltages and CM wave form distortion at each constant sound pressure. The results obtained were as follows: (1) On the 50 microV isopotential response curve and the output voltage curves, the changes at 60-90 Hz were different from those at higher frequencies. (2) At stimuli of 90 or 100 dB(SPL), CM wave form distortion appeared frequently at frequencies below 120 Hz, but were less pronounced above approximately 200 Hz. (3) When raised to 110 and 120 dB(SPL), almost all CM wave forms were distorted at all test frequencies between 60 and 500 Hz. (4) The patterns of CM wave form distortion at frequencies below approximately 120 Hz showed peak clipping and triangular wave distortions, while those at frequencies above approximately 200 Hz showed little of these distortions.     

Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii.

Pteronotus parnellii uses the second harmonic (61-62 kHz) of the CF component in its orientation sounds for Doppler-shift compensation. The bat's inner ear is mechanically specialized for fine analysis of sounds at about 61-62 kHz. Because of this specialization, cochlear microphonics (CM) evoked by 61-62 kHz tone bursts exhibit prominent transients, slow increase and decrease in amplitude at the onset and cessation of these stimuli. CM-responses to 60-61 kHz tone bursts show a prominent input-output non-linearity and transients. Accordingly, a summated response of primary auditory neurones (N1) appears not only at the onset of the stimuli, but also at the cessation. N1-off is sharply tuned at 60-61 kHz, while N1-on is tuned at 63-64 kHz, which is 2 kHz higher than the best frequency of the auditory system because of the envelope-distortion originating from sharp mechanical tuning. Single peripheral neurones sensitive to 61-62 kHz sounds have an unusually sharp tuning curve and show phase-locked responses to beats of up to 3 kHz. Information about the frequencies of Doppler-shifted echoes is thus coded by a set of sharply tuned neurones and also discharges phase-locked to beats. Neurones with a best frequency between 55 and 64 kHz show not only tonic on-responses but also off-responses which are apparently related to the mechanical off-transient occuring in the inner ear and not to a rebound from neural inhibition.     

Frequency and temporal pattern-dependent phonotaxis of crickets (Teleogryllus oceanicus) during tethered flight and compensated walking

Summary Phonotactic responses ofTeleogryllus oceanicus were studied with two methods. Tethered crickets were stimulated with sound while they performed stationary flight, and steering responses were indicated by abdominal movements. Walking crickets tracked a sound source while their translational movements were compensated by a spherical treadmill, and their walking direction and velocity were recorded.During both flight and walking, crickets attempted to locomote towards the sound source when a song model with 5 kHz carrier frequency was broadcast (positive phonotactic response) and away from the source when a song model with 33 kHz carrier frequency was used (negative phonotactic response) (Figs. 2, 4).One-eared crickets attempted, while flying, to steer towards the side of the remaining ear when stimulated with the 5 kHz model, and away from that side in response to the 33 kHz model (Fig. 3). While walking, one-eared crickets circled towards and away from the intact side in response to the 5 kHz and 33 kHz models, respectively (Fig. 6).Positive and negative responses differed in their temporal pattern requirements. Phonotactic responses were not elicited when a non-calling song pattern (2 pulses/s) was played with a carrier frequency appropriate for positive phonotactic responses (5 kHz), but this pattern did elicit negative responses with 33 kHz carrier frequency (Figs. 7–10). When an intermediate carrier frequency, 15 kHz, was used, the response type (positive or negative) depended on the stimulus temporal pattern; the calling song pattern elicited primarily positive responses, while the non-calling song pattern elicited negative responses (Figs. 11, 12, 14, 15). A curious phenomenon was often observed in the flight steering responses; while most responses to 15 kHz song pattern were primarily positive, they often had an initial negative component which was supplanted by the positive component of the response after approximately 2–5 s (Figs. 11, 12).In recent experiments onGryllus campestris, Thorson et al. (1982) described frequency-dependent errors in phonotactic direction (anomalous phonotaxis) and showed how such errors might arise from the frequency-dependent directional properties of the cricket's auditory apparatus. Our findings, particularly the dependence of response type on temporal pattern when 15 kHz carrier frequency was used, argue that frequency-dependent directional properties alone cannot account for positive and negative phonotaxis inT. oceanicus. Rather, these represent qualitatively different attempts to locomote towards and away from the sound source, respectively.We discuss the possibility that central integration of these opposing tendencies might contribute to anomalous phonotaxis.     

Directional hearing in the barn owl (Tyto alba)

Summary The acoustical properties of the external ear of the barn owl (Tyto alba) were studied by measuring sound pressure in the ear canal and outer ear cavity. Under normal conditions, pressure amplification by the external ear reaches about 20 dB between 3–9 kHz but decreases sharply above 10 kHz. The acoustic gain curve of the outer ear cavity alone is close to that of a finite-length exponential horn between 1.2–13 kHz with maximum gain reaching 20 dB between 5–9 kHz. Pressure gain by the facial ruff produces a maximum of 12 dB between 5–8 kHz and decreases rapidly above 9 kHz.The directional sensitivity of the external ear was obtained from pressure measurements in the ear canal. Directivity of the major lobe is explained, to a first approximation, by the sound diffraction properties of a circular aperture. Aperture size is based on the average radius (30 mm) of the open face of the ruff. Above 5 kHz, the external ear becomes highly directional and there is a 26° disparity in elevation between the acoustic axis of the left and right ear. In azimuth, directivity patterns are relocated closer to the midline as frequency increases and the acoustic axis moves at a rate of 20°/octave between 2–13 kHz. Movement of the axis can be explained, to a first approximation, by the acoustical diffraction properties of an obliquely truncated horn, due to the asymmetrical shape of the outer ear cavity.The directional sensitivity of the barn owl ear was studied by recording cochlear microphonic (CM) potentials from the round window membrane. Between 3–9 kHz, CM directivity patterns are clearly different to the directivity patterns of the external ear; CM directionality is abruptly lost above 10 kHz. Above 5 kHz, CM directivity patterns are characterized by an elongated major lobe containing the CM axis, forming a tilted band of high amplitude but low directionality (CM axial plane), closely bordered by minima or nulls. The highest directionality is found in theCM directional plane, approximately perpendicular to the CM axial plane. The left and right ear axial planes are symmetrical about the interaural midline (tilted 12° to the right of the midline of the head) and inclined by an average of 60° to the left and right respectively. In azimuth, the CM axis moves towards the midline at a rate of 37°/octave as frequency increases from 2–9 kHz, crossing into contralateral space near 7 kHz. In the CM directional plane, the directivity of the major lobe suggests that a pressure gradient may occur at the TM. The region of frontal space mapped by movement of the CM axis in azimuth closely matches the angle of sound incidence which would be expected to produce the maximum driving pressure at the TM. It is suggested that acoustical interference at the TM results from sound transmission through the interaural canal and therefore the ear is inherently directional. It is proposed that ear directionality in the barn owl may be explained by the combined effect of sound diffraction by the outer ear cavity and a pressure gradient at the TM.Abbreviations CM cochlear microphonic - RMS root mean square - SPL sound pressure level - TM tympanic membrane     

Auditory cortex basal activity modulates cochlear responses in chinchillas

Background

The auditory efferent system has unique neuroanatomical pathways that connect the cerebral cortex with sensory receptor cells. Pyramidal neurons located in layers V and VI of the primary auditory cortex constitute descending projections to the thalamus, inferior colliculus, and even directly to the superior olivary complex and to the cochlear nucleus. Efferent pathways are connected to the cochlear receptor by the olivocochlear system, which innervates outer hair cells and auditory nerve fibers. The functional role of the cortico-olivocochlear efferent system remains debated. We hypothesized that auditory cortex basal activity modulates cochlear and auditory-nerve afferent responses through the efferent system.

Methodology/Principal Findings

Cochlear microphonics (CM), auditory-nerve compound action potentials (CAP) and auditory cortex evoked potentials (ACEP) were recorded in twenty anesthetized chinchillas, before, during and after auditory cortex deactivation by two methods: lidocaine microinjections or cortical cooling with cryoloops. Auditory cortex deactivation induced a transient reduction in ACEP amplitudes in fifteen animals (deactivation experiments) and a permanent reduction in five chinchillas (lesion experiments). We found significant changes in the amplitude of CM in both types of experiments, being the most common effect a CM decrease found in fifteen animals. Concomitantly to CM amplitude changes, we found CAP increases in seven chinchillas and CAP reductions in thirteen animals. Although ACEP amplitudes were completely recovered after ninety minutes in deactivation experiments, only partial recovery was observed in the magnitudes of cochlear responses.

Conclusions/Significance

These results show that blocking ongoing auditory cortex activity modulates CM and CAP responses, demonstrating that cortico-olivocochlear circuits regulate auditory nerve and cochlear responses through a basal efferent tone. The diversity of the obtained effects suggests that there are at least two functional pathways from the auditory cortex to the cochlea.     

Response properties of primary auditory fibers in the cricketTeleogryllus oceanieus (Le Guillou)

Summary Single unit recordings of primary auditory fibers ofTeleogryllus oceanicus show responses to frequencies over the range 0.5 kHz to 42 kHz. The characteristic frequencies (ChFs) of units were distributed over much of the bandwidth investigated although few units were recorded with ChFs below 4 kHz or in the region 7 kHz to 10 kHz. Some units showed more than one peak of sensitivity and others were broad-banded with no tuning to a particular frequency. Units whose ChFs approximated to the carrier frequency (CF) of the proclamation song were the most highly tuned. The majority of units had a tonic response pattern and were not spontaneously active. The implications of these findings are discussed.Abbreviations ChF characteristic frequency - CF carrier frequency We thank Mr. P. Foster for techninical help.     

Auditory evoked potentials in the Japanese monkey.

Auditory sensitivity based on auditory brain stem response (ABR), whole nerve action potential (AP), and cochlear microphonics (CM) to tone bursts of 0.5-8 kHz were compared with behavioral audiometry in the Japanese monkeys. Although sensitivity loss at 4-6 kHz was observed in these potentials, an increase in sensitivity at 8 kHz was obtained only in the ABR. Thus the sensitivity loss at 4-6 kHz originates at the peripheral system and the increased sensitivity at 8 kHz originates at the central.     

Modulation rate transfer functions in bottlenose dolphins (<Emphasis Type="Italic">Tursiops truncatus</Emphasis>) with normal hearing and high-frequency hearing loss

Envelope following responses were measured in two bottlenose dolphins in response to sinusoidal amplitude modulated tones with carrier frequencies from 20 to 60 kHz and modulation rates from 100 to 5,000 Hz. One subject had elevated hearing thresholds at higher frequencies, with threshold differences between subjects varying from ±4 dB at 20 and 30 kHz to +40 dB at 50 and 60 kHz. At each carrier frequency, evoked response amplitudes and phase angles were plotted with respect to modulation frequency to construct modulation rate transfer functions. Results showed that both subjects could follow the stimulus envelope components up to at least 2,000 Hz, regardless of carrier frequency. There were no substantial differences in modulation rate transfer functions for the two subjects suggesting that reductions in hearing sensitivity did not result in reduced temporal processing ability. In contrast to earlier studies, phase data showed group delays of approximately 3.5 ms across the tested frequency range, implying generation site(s) within the brainstem rather than the periphery at modulation rates from 100 to 1,600 Hz. This discrepancy is believed to be the result of undersampling of the modulation rate during previous phase measurements.     

腺苷对豚鼠耳蜗功能的影响

腺苷作为一种神经调质,能抑制多种递质的释放,发挥负反馈调节作用,用外淋巴灌流给药方法,观察了腺苷及其摄取抑制剂双嘧啶氨醇、受体拮抗剂茶 对豚鼠复合听神经动作电位、微音器电位、蜗内直流电位的影响。     

Beaked whale auditory evoked potential hearing measurements

Several mass strandings of beaked whales have recently been correlated with military exercises involving mid-frequency sonar highlighting unknowns regarding hearing sensitivity in these species. We report the hearing abilities of a stranded juvenile beaked whale (Mesoplodon europaeus) measured with auditory evoked potentials. The beaked whale’s modulation rate transfer function (MRTF) measured with a 40-kHz carrier showed responses up to an 1,800 Hz amplitude modulation (AM) rate. The MRTF was strongest at the 1,000 and 1,200 Hz AM rates. The envelope following response (EFR) input–output functions were non-linear. The beaked whale was most sensitive to high frequency signals between 40 and 80 kHz, but produced smaller evoked potentials to 5 kHz, the lowest frequency tested. The beaked whale hearing range and sensitivity are similar to other odontocetes that have been measured.     

Resonance phenomena in the cochlea of the mustache bat and their contribution to neuronal response characteristics in the cochlear nucleus

Summary The cochlea of the mustache bat, Pteronotus parnellii, is very sensitive and sharply tuned to the frequency range of the dominant second harmonic of the echolocation call around 61 kHz. About 900 Hz above this frequency the cochlear microphonic potential (CM) reaches its maximum amplitude and lowest threshold. At exactly the same frequency, pronounced evoked otoacoustic emissions (OAE) can be measured in the outer ear canal, indicating mechanical resonance. The CM amplitude maximum and the OAE are most severely masked by simultaneous exposure to tones within the range from about 61–62 kHz up to about 70 kHz. The data suggest that the mechanism of mechanical resonance involves cochlear loci basal to the 61 kHz position.The resonance contributes to auditory sensitivity and sharp tuning: At the frequency of the OAE, single unit responses in the cochlear nucleus have the lowest thresholds. Maximum tuning sharpness occurs at frequencies about 300 Hz below the OAE-frequency, where the threshold is about 10 dB less sensitive than at the OAE-frequency. In addition, in the frequency range around the OAE-frequency several specialized neuronal response features can be related to mechanical resonance: Long lasting excitation after the end of the stimulus, asymmetrical tuning curves with a shallow high frequency slope and phasic on-off neuronal response patterns. In particular the latter phenomenon indicates the occurrence of local mechanical cancellations in the cochlea.Abbreviations CF constant frequency component of echolocation calls - CM cochlear microphonic potential - FM frequency modulated component of echolocation calls - N1 compound action potential of the auditory nerve - OAE octoacoustic emission - SEOAE synchronous evoked OAE     

Mitotic segregation of cytoplasmic determinants for chloramphenicol resistance in mammalian cells. I: Fusion with mouse cell lines

The segregation of cytoplasmically inherited chloramphenicol (CAP) resistance in mouse cells was investigated in fusions between CAP-resistant cells or cytoplasts (enucleated cells) and CAP-sensitive cells of varying tissue origin. All hybrids formed in cell-cell fusions were initially CAP-resistant, indicating that CAP resistance is dominant. Hybrids from fusions of cells of the same tissue origin (homologous) were stably CAP-resistant, whereas the hybrid population from fusions of different origins (heterologous) showed a rapid diminution of average CAP resistance. Individual hybrid clones from these heterologous fusions also showed an overall loss of CAP resistance, and a wide variation in CAP resistance which is consistent with a large number of genetic determinants (possibly mitochondrial DNA molecules) contributing to the CAP phenotype. Similar results were obtained from cytoplast-cell fusions, so the observed CAP segregation is not the result of nuclear-nuclear interactions. This segregation of CAP resistance constitutes a second criterion of cytoplasmic inheritance in mammalian cells.     

An Overrepresentation of High Frequencies in the Mouse Inferior Colliculus Supports the Processing of Ultrasonic Vocalizations

Mice are of paramount importance in biomedical research and their vocalizations are a subject of interest for researchers across a wide range of health-related disciplines due to their increasingly important value as a phenotyping tool in models of neural, speech and language disorders. However, the mechanisms underlying the auditory processing of vocalizations in mice are not well understood. The mouse audiogram shows a peak in sensitivity at frequencies between 15-25 kHz, but weaker sensitivity for the higher ultrasonic frequencies at which they typically vocalize. To investigate the auditory processing of vocalizations in mice, we measured evoked potential, single-unit, and multi-unit responses to tones and vocalizations at three different stages along the auditory pathway: the auditory nerve and the cochlear nucleus in the periphery, and the inferior colliculus in the midbrain. Auditory brainstem response measurements suggested stronger responses in the midbrain relative to the periphery for frequencies higher than 32 kHz. This result was confirmed by single- and multi-unit recordings showing that high ultrasonic frequency tones and vocalizations elicited responses from only a small fraction of cells in the periphery, while a much larger fraction of cells responded in the inferior colliculus. These results suggest that the processing of communication calls in mice is supported by a specialization of the auditory system for high frequencies that emerges at central stations of the auditory pathway.     

The spectral structure of vocalizations match hearing sensitivity but imprecisely in Philautus odontotarsus

It is generally thought that for species using vocal communication the spectral properties of the sender’s calls should match the frequency sensitivity of the receiver’s auditory system. Nevertheless, few studies have investigated both sender and receiver characteristics in anuran species. In the present study, auditory brainstem responses (ABRs) were recorded in the serrate legged treefrog, Philautus odontotarsus, in order to determine if male call spectral structure and hearing sensitivity in males and females have co-evolved in this species. The results showed that the spectral structures of male vocalization match both male and female hearing sensitivity, even though the dominant frequencies of male calls (2.5 kHz) are mismatched with the regions of best frequency sensitivity (1.4 and 2.8 kHz). In addition, the results show that, in contrast with most previous ABR studies in non-human animals, but consistent with human studies, there are noticeable sex differences in peripheral auditory sensitivity in Philautus insofar as females exhibit lower auditory thresholds than males across the entire 1.8–18 kHz frequency range. The results also show that the dominant frequency of male calls is negatively correlated with body size, indicating that call characteristics reflect body size in this species which may be used by females during mate choice.     

Hearing in reindeer (Rangifer tarandus)

The audiogram of two yearling male reindeer (Rangifer tarandus tarandus) were determined using a conditioned suppression/avoidance procedure. During testing, the animal was drinking from a metal bowl while pure tone signals were played at random intervals and followed by an electric shock in the bowl. By breaking contact with the bowl at sound signals, the animal avoided the shock. The animals detected sounds at intensities of 60 dB or less from 70 Hz to 38 kHz. The frequency range of best sensitivity was relatively flat from 1 kHz to 16 kHz, with a best sensitivity of 3 dB at 8 kHz. The hearing ability of reindeer is similar to the hearing ability of other ungulates.     

Synaptic inputs to the omega neuron of the cricket Teleogryllus oceanicus: differences in EPSP waveforms evoke by low and high sound frequencies

EPSP waveforms were recorded from the omega neuron of Teleogryllus oceanicus for 5 kHz and ultrasonic sound stimuli. EPSPs in response to 5 kHz stimuli were smooth in shape and increased in amplitude with increasing stimulus intensity, while responses to ultrasound consisted of series' of large, discrete, unitary EPSPs, which increased in frequency with stimulus intensity.The hypothesis that a few, synaptically potent receptors might account for ultrasound sensitivity was tested by examining temporal coupling between ultrasound responses of the omega neuron and of another ultrasound-sensitive neuron, INT-1. INT-1 spikes were temporally correlated both to omega neuron spikes and to the large EPSPs recorded in the omega neuron. Coupling was not apparent for 5 kHz stimuli.The omega neuron encodes the intensity of 5 kHz and ultrasonic stimuli with similar resolution. Response latencies are markedly shorter for ultrasonic stimuli.These findings suggest that 5 kHz information is carried by a relatively large number of receptors, each of which has only a small effect on central neurons, while ultrasound information is carried by a few, synaptically potent, receptors.