Properties of low-frequency head-related transfer functions in the barn owl (Tyto alba)

The barn owl (Tyto alba) possesses several specializations regarding auditory processing. The most conspicuous features are the directionally sensitive facial ruff and the asymmetrically arranged ears. The frequency-specific influence of these features on sound has consequences for sound localization that might differ between low and high frequencies. Whereas the high-frequency range (>3 kHz) is well investigated, less is known about the characteristics of head-related transfer functions for frequencies below 3 kHz. In the present study, we compared 1/3 octaveband-filtered transfer functions of barn owls with center frequencies ranging from 0.5 to 9 kHz. The range of interaural time differences was 600 μs at frequencies above 4 kHz, decreased to 505 μs at 3 kHz and increased again to about 615 μs at lower frequencies. The ranges for very low (0.5–1 kHz) and high frequencies (5–9 kHz) were not statistically different. Interaural level differences and monaural gains increased monotonically with increasing frequency. No systematic influence of the body temperature on the measured localization cues was observed. These data have implications for the mechanism underlying sound localization and we suggest that the barn owl’s ears work as pressure receivers both in the high- and low-frequency ranges.     

Frequency tuning curves of the dolphin's hearing: envelope-following response study

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in dolphins (Turslops truncatus). The EFR was evoked by amplitude-modulated probes of various frequencies. A modulation rate of 600 Hz was found to fit the requirement to have a narrow spectrum and evoke EFR of large amplitude. Tuning curves were obtained within the frequency range from 11.2 to 110 kHz. The Q₁₀ values of the obtained tuning curves varied from 12–14 at the 11.2 kHz center frequency to 17–20 at the 64–90 kHz frequencies.Abbreviations ABR auditory brainstem response - EFR envelope following response - ERB equivalent rectangular bandwidth     

The electro-optical investigation of suspensions of Escherichia coli K-12 cells metabolizing glucose,lactose, and galactose

The electro-optical characteristics of suspensions of Escherichia coli K-12 cells metabolizing glucose, lactose, and galactose were studied my measuring the suspension turbidity as a function of cell alignment in an orienting electric field whose frequency was varied from 10 kHz to 10 MHz. In a frequency range of 10 kHz to 1 MHz, the orientational spectra of E. coli K-12 cells grown on glucose and lactose considerably changed after their incubation in the presence of the sugars. These changes likely reflect alterations in the polarizability of the cells induced by sugar metabolism.     

Characteristics of transverse electric and magnetic field transmission cells at extremely low frequencies

Transverse electric and magnetic field (TEM) cells are often designed to subject samples to electromagnetic radiation of intrinsic impedance (E/H) that is the same as in free space, 377 omega. Earlier work has shown this value to be correct for the RF region above about 2 kHz. In this study, measurements of magnetic fields in the extremely low frequency regions and at DC indicate the E/H ratio to be around 300 omega for frequencies less than 2 kHz in cells of a particular design. This lower value indicates that care should be taken in estimating AC magnetic field intensities from electric field measurements in TEM cells at frequencies below 2 kHz.     

The Electro-Optical Investigation of Suspensions of Escherichia coli K-12 Cells Metabolizing Glucose,Lactose, and Galactose

The electro-optical characteristics of suspensions of Escherichia coli K-12 cells metabolizing glucose, lactose, and galactose were studied by measuring the suspension turbidity as a function of cell alignment in an orienting electric field whose frequency was varied from 10 kHz to 10 MHz. In a frequency range of 10 kHz to 1 MHz, the orientational spectra of E. coli K-12 cells grown on glucose and lactose considerably changed after their incubation in the presence of the sugars. These changes likely reflect alterations in the polarizability of the cells induced by sugar metabolism.     

Hearing conspecific vocal signals alters peripheral auditory sensitivity

We investigated whether hearing advertisement calls over several nights, as happens in natural frog choruses, modified the responses of the peripheral auditory system in the green treefrog, Hyla cinerea. Using auditory evoked potentials (AEP), we found that exposure to 10 nights of a simulated male chorus lowered auditory thresholds in males and females, while exposure to random tones had no effect in males, but did result in lower thresholds in females. The threshold change was larger at the lower frequencies stimulating the amphibian papilla than at higher frequencies stimulating the basilar papilla. Suprathreshold responses to tonal stimuli were assessed for two peaks in the AEP recordings. For the peak P1 (assessed for 0.8–1.25 kHz), peak amplitude increased following chorus exposure. For peak P2 (assessed for 2–4 kHz), peak amplitude decreased at frequencies between 2.5 and 4.0 kHz, but remained unaltered at 2.0 kHz. Our results show for the first time, to our knowledge, that hearing dynamic social stimuli, like frog choruses, can alter the responses of the auditory periphery in a way that could enhance the detection of and response to conspecific acoustic communication signals.     

Production of sound waves by bacterial cells and the response of bacterial cells to sound

Bacterial cells enhance the proliferation of neighboring cells under stress conditions by emitting a physical signal. Continuous single sine sound waves produced by a speaker at frequencies of 6-10, 18-22, and 28-38 kHz promoted colony formation by Bacillus carboniphilus under non-permissive stress conditions of high KCl concentration and high temperature. Furthermore, sound waves emitted from cells of Bacillus subtilis at frequencies between 8 and 43 kHz with broad peaks at approximately 8.5, 19, 29, and 37 kHz were detected using a sensitive microphone system. The similarity between the frequency of the sound produced by B. subtilis and the frequencies that induced a response in B. carboniphilus and the previously observed growth-promoting effect of B. subtilis cells upon B. carboniphilus through iron barriers, suggest that the detected sound waves function as a growth-regulatory signal between cells.     

Development of chick embryos in 1 Hz to 100 kHz magnetic fields

Summary Chick embryos were exposed during their 48 first hours of development to sinusoidally oscillating magnetic fields. The frequencies 1 Hz, 10 Hz, 16.7 Hz, 30 Hz, 50 Hz, 1 kHz, 10 kHz and 100 kHz, and the field strengths 0.1, 1, 10 and 100 A/m were used. Each exposure group consisted of 20 eggs. After the exposure, the embryos were examined for abnormalities and classified by the developmental stage. The percentage of abnormal embryos (%AE) was significantly increased at frequencies from 16.7 Hz to 100 kHz. Above a threshold field strength of about 0.1 to 1 A/m, %AE was rather independent of the field strength, varying from 16% to 56% in different exposure groups. 13% of the sham-exposed control embryos (n = 150) were abnormal. Only the 0.1 A/m exposure group differed significantly from the controls at 1 Hz, and no significant effect was found at 10 Hz. The developmental stage was in general not affected by the magnetic fields, but some abnormal embryos showed retarded development.     

The effect of acute alcohol administration on auditory evoked potentials in altricial nestlings during the development of natural behavior]

Acute ethanol influence on field L auditory evoked potentials (AEP) was studied in 4-8-days-old altricial nestlings of pied flycatcher. Nestlings were presented with tone pips related with the realization of natural behaviour (2.0 and 5.0 kHz) and bearing no meaning for the behaviour of the young of the age under study (3.0 kHz). Ethanol ingestion was found to reduce the maturity index (MI) of AEP in response to "behavioural" but not to control frequencies; this effect was first observed at day 5, when nestlings eyes opened and defence behaviour appeared, while previously formed feeding behaviour was significantly modified. During the next 2 days alcohol had a greater effect upon the AEP in response to 2.0 kHz tone pips, related with feeding behaviour of increasing complexity than upon the AEP in response to 5.0 kHz, related with the defence behaviour that remained relatively constant. The previous data concerning the effect of alcohol on unit activity are used to support the view that MI increase during the early postembryonic ontogeny is due to the involvement of neurons with newly formed behavioural specializations into the subserving of new behavioural patterns while the decrease of MI under alcohol is due to the depression of activity in these neurons.     

Modified Protein Expression in the Tectorial Membrane of the Cochlea Reveals Roles for the Striated Sheet Matrix

The tectorial membrane (TM) of the mammalian cochlea is a complex extracellular matrix which, in response to acoustic stimulation, displaces the hair bundles of outer hair cells (OHCs), thereby initiating sensory transduction and amplification. Here, using TM segments from the basal, high-frequency region of the cochleae of genetically modified mice (including models of human hereditary deafness) with missing or modified TM proteins, we demonstrate that frequency-dependent stiffening is associated with the striated sheet matrix (SSM). Frequency-dependent stiffening largely disappeared in all three TM mutations studied where the SSM was absent either entirely or at least from the stiffest part of the TM overlying the OHCs. In all three TM mutations, dissipation of energy is decreased at low (<8 kHz) and increased at high (>8 kHz) stimulus frequencies. The SSM is composed of polypeptides carrying fixed charges, and electrostatic interaction between them may account for frequency-dependent stiffness changes in the material properties of the TM. Through comparison with previous in vivo measurements, it is proposed that implementation of frequency-dependent stiffening of the TM in the OHC attachment region facilitates interaction among tones, backward transmission of energy, and amplification in the cochlea.     

Characterization of Dynamic Behaviour of MCF7 and MCF10A Cells in Ultrasonic Field Using Modal and Harmonic Analyses

Treatment options specifically targeting tumour cells are urgently needed in order to reduce the side effects accompanied by chemo- or radiotherapy. Differences in subcellular structure between tumour and normal cells determine their specific elasticity. These structural differences can be utilised by low-frequency ultrasound in order to specifically induce cytotoxicity of tumour cells. For further evaluation, we combined in silico FEM (finite element method) analyses and in vitro assays to bolster the significance of low-frequency ultrasound for tumour treatment. FEM simulations were able to calculate the first resonance frequency of MCF7 breast tumour cells at 21 kHz in contrast to 34 kHz for the MCF10A normal breast cells, which was due to the higher elasticity and larger size of MCF7 cells. For experimental validation of the in silico-determined resonance frequencies, equipment for ultrasonic irradiation with distinct frequencies was constructed. Differences for both cell lines in their response to low-frequent ultrasonic treatment were corroborated in 2D and in 3D cell culture assays. Treatment with ~ 24.5 kHz induced the death of MCF7 cells and MDA-MB-231 metastases cells possessing a similar elasticity; frequencies of > 29 kHz resulted in cytotoxicity of MCF10A. Fractionated treatments by ultrasonic irradiation of suspension myeloid HL60 cells resulted in a significant decrease of viable cells, mostly significant after threefold irradiation in intervals of 3 h. Most importantly in regard to a clinical application, combined ultrasonic treatment and chemotherapy with paclitaxel showed a significantly increased killing of MCF7 cells compared to both monotherapies. In summary, we were able to determine for the first time for different tumour cell lines a specific frequency of low-intensity ultrasound for induction of cell ablation. The cytotoxic effect of ultrasonic irradiation could be increased by either fractionated treatment or in combination with chemotherapy. Thus, our results will open new perspectives in tumour treatment.     

The ontogenetic development of auditory sensitivity, vocalization and acoustic communication in the labyrinth fish Trichopsis vittata

The anabantoid fish Trichopsis vittata starts vocalizing as 8-week-old juveniles. In order to determine whether juveniles are able to detect conspecific sounds, hearing sensitivities were measured in six size groups utilizing the auditory brainstem response-recording technique. Results were compared to sound pressure levels and spectra of sounds recorded during fighting. Auditory evoked potentials were present in all size groups and complete audiograms were obtained starting with 0.18 to 0.30 g juveniles. Auditory sensitivity during development primarily increased between 0.8 kHz and 3.0 kHz. The most sensitive frequency within this range shifted from 2.5 kHz to 1.5 kHz, whereas thresholds decreased by 14 dB. Sound production, on the other hand, started at 0.1 g and sound power spectra at dominant frequencies increased by 43 dB, while dominant frequencies shifted from 3 kHz to 1.5 kHz. Comparisons between audiograms and sound power spectra in similar-sized juveniles revealed no clear match between most sensitive frequencies and dominant frequencies of sounds. This also revealed that juveniles cannot detect conspecific sounds below the 0.31 to 0.65 g size class. These results indicate that auditory sensitivity develops prior to the ability to vocalize and that vocalization occurs prior to the ability to communicate acoustically.     

Characteristics of evoked potentials and single neuron responses in the cat sensorimotor cortex to sound stimuli with different frequencies.

The characteristics of the averaged evoked potentials (AEP) (experiments with awake non-paralysed animals), of the evoked potentials (EP) and of the responses of single sensorimotor cortical neurons (acute experiments) of cats to tone-bursts with frequencies within 0.1-6.0 kHz were studied. Response selectivity to the tone-burst frequencies which are energetically pronounced in some biologically significant sounds for the cat was observed. The averaged curve of the dependence of the amplitude of AEP in the somatosensory cortical region (S1) on the tone-burst frequency has reliable maximum values at the frequencies of 0.8, 1.6 and 2.0-3.0 kHz. Most pronounced changes in the heart rhythm were observed within the tone-burst frequency ranges in which the AEP of the highest amplitudes were recorded. The amplitude of the AEP was found to increase during the conditioned reflex elaboration. The curve of the dependence of the probability of the EP occurrence on the frequency at equal sound pressure levels had maximum values at the frequencies of 1.6 and 3.2 kHz. The highest amplitude values of EP were found at frequencies of 0.8, 1.6 and 3.2 kHz. More than half of the recorded neurons revealed the lowest values of the response thresholds and the maximum values of the occurrence probability under suprathreshold stimulation at frequencies close to 0.8, 1.6, and 3.2 kHz. It is supposed that the above mentioned feature of the input frequency organization in sensorimotor cortex is connected with the selectivity as to the biological significance of acoustic stimuli.     

Modulation of cytokine production by interferential current in differentiated HL-60 cells

The influence of interferential current (IFC) on the release of four cytokines was investigated. IFC is an amplitude-modulated 4 kHz current used in therapeutic applications. Human promyelocytes (HL-60) were differentiated to monocytes/macrophages by treatment with calcitriol. Release of tumor necrosis factor alpha (TNFalpha) and interleukines 1beta, 6, and 8 (IL-1beta, IL-6, and IL-8) into the supernatant was measured after exposure to IFC at different modulation frequencies. TNFalpha release was stimulated about twofold by 4 kHz sine waves alone. The influences of exposure time (5-30 min) and current density (2.5-2500 microA/c m(2)) were tested. A maximum field effect was found at an exposure time of 15 min and a current density of 250 microA/cm(2). With these exposure conditions (15 min and 250 microA/cm(2) ), cells were treated at different modulation frequencies and reacted for TNFalpha, IL-1beta, and IL-8 release in a complex manner. Within the frequencies studied (0-125 Hz), we found stimulation as well as depression of the release. In a second run the cells were activated by pretreatment with 10 microg/ml lipopolysaccharide (LPS) and exposed in the same way as the nonactivated cells. Again the modulation frequency influenced, in a complex way, the induction of TNFalpha, IL-1beta, and IL-8, resulting in a pattern of stimulation and depression of release different from that found in nonactivated cells. For IL-6 production no significant changes were detected in activated or non-activated cells.     

The development of hearing sensitivity in altricial birds: the absolute thresholds of the generation of evoked potentials]

Thresholds of field L auditory evoked potentials EP were studied in 1.5-9-day-old nestlings of pied flycatcher in response to pure tone signals of different frequencies. According to the tendencies of age dynamics of auditory EP thresholds (2-9 days of life) all hearing range was divided into three separate channels: low-frequency (0.3-1.0 kHz), intermediate-(1.5-4.0 kHz) and high-frequency (5.0-8.0 kHz) ones. The widening of the hearing range in its high-frequency part was demonstrated on days 4-5 of life. The development of auditory sensitivity was shown to continue within all three channels in postembryonic period (days 2-9 post-hatching), each of the channels being characterized by its own age dynamics of auditory EP thresholds. Reproduction of tape-recorded species song during days 1-3 post-hatching resulted in significant decrease of auditory EP thresholds.     

Ultrasonic startle behavior in bushcrickets (Orthoptera; Tettigoniidae)

1. In the present work, we show that in flight, bushcrickets not previously known to respond to ultrasound alter their flight course in response to ultrasonic stimuli. Such stimuli elicit in flying Neoconocephalus ensiger an extension of the front and middle legs along the body and a rapid closure of all 4 wings (Fig. 1). This is a short latency acoustic startle response to ultrasound, consistent with acoustic startle responses of other insects. 2. The percentage of trials on which acoustic startle responses were elicited was maximum (90%) for sound frequencies ranging from 25 to at least 60 kHz. No acoustic startle response was observed at frequencies of 5 or 10 kHz (Fig. 2). The threshold for the response was roughly 76 dB between 25 to 60 kHz (Fig. 2) and the behavioral latency was 45 ms (Fig. 3). Recordings from flight muscles show that they cease discharging during the acoustic startle response (Fig. 4). 3. The characteristics of the acoustic startle response match those of an auditory interneuron called the T-neuron. The frequency sensitivity of this neuron is greatest for sound frequencies ranging from 13 to 60 kHz (Fig. 6). Moreover, we found that the neuron produces many more spikes to ultrasound (30 kHz) of increasing intensities than to a conspecific communication sound, whose dominant frequency is 14 kHz (Fig. 7).     

Physiology and tonotopic organization of auditory receptors in the cricketGryllus bimaculatus DeGeer

Summary Physiological recordings were obtained from identified receptors in the tympanal organ ofGryllus bimaculatus. By immersing the prothoracic leg in Ringer solution and removing the anterior tympanic membrane the auditory receptors were exposed without significantly altering the frequency response of the auditory organ (Fig. 1). Each receptor was tuned to a specific sound frequency. For sound frequencies below this characteristic frequency the roll-off in sensitivity decreased from 20–30 dB/octave to 10–15 dB/octave as the characteristic frequency of receptors increased from 3–11 kHz (Fig. 4A). For each individual receptor the slope, dynamic range and maximum spike response were similar for different sound frequencies (Fig. 9A). The receptors were tonotopically organized with the characteristic frequency of the receptors increasing from the proximal to the distal end of the array (Figs. 5, 6). Several receptors had characteristic frequencies of 5 kHz. These receptors were divided into two groups on the basis of their maximum spike response produced in response to pure tones of increasing intensity (Fig. 7). Independent of the tuning of the receptor no two-tone inhibition was observed in the periphery, thus confirming that such interactions are a property of central integration.     

Dynamics of the changes of electrophysical properties of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp7 cells at their binding with wheat germ agglutinin

The electrooptical properties of Azospirillum brasilense Sp7 cell suspensions, have been studied at a specific interaction with wheat germ agglutinin (WGA), using the dependences between the changes of optical densities of cell suspensions at the electric orientation of cells and the orienting field frequencies of 740, 1000, 1450, 2000, and 2800 kHz. It was shown that the electrooptical (EO) properties of cell suspensions changed at the interaction of A. brasilense Sp7 cells with WGA and that the EO signal value changed irrespective of the cultivation conditions. At the same time, the dynamics of the changes of the EO properties of microbial suspensions was different for microbial cells grown under different conditions. It may be evidence of the differences in the cell surface properties of microbial cells, and of the dependence, between bacterial response to lectin and growth conditions. The possibility of using the EO analysis of bacterial suspensions for the study of the high-specific binding of polypeptide molecular signals with the bacterial target cells and for assessment of the dynamics of this process has been demonstrated.     

Phonotaxis in flying crickets

The steering responses of three species of field crickets, Teleogryllus oceanicus, T. commodus, and Gryllus bimaculatus, were characterized during tethered flight using single tone-pulses (rather than model calling song) presented at carrier frequencies from 3-100 kHz. This range of frequencies encompasses the natural songs of crickets (4-20 kHz, Fig. 1) as well as the echolocation cries of insectivorous bats (12-100 kHz). The single-pulse stimulus paradigm was necessary to assess the aversive nature of high carrier frequencies without introducing complications due to the attractive properties of repeated pulse stimuli such as model calling songs. Unlike the natural calling song, single tone-pulses were not attractive and did not elicit positive phonotactic steering even when presented at the calling song carrier frequency (Figs. 2, 3, and 9). In addition to temporal pattern, phonotactic steering was sensitive to carrier frequency as well as sound intensity. Three discrete flight steering behaviors positive phonotaxis, negative phonotaxis and evasion, were elicited by appropriate combinations of frequency, temporal pattern and sound intensity (Fig. 12). Positive phonotactic steering required a model calling song temporal pattern, was tuned to 5 kHz and was restricted to frequencies below 9 kHz. Negative phonotactic steering, similar to the 'early warning' bat-avoidance behavior of moths, was produced by low intensity (55 dB SPL) tone-pulses at frequencies between 12 and 100 kHz (Figs. 2, 3, and 9). In contrast to model calling song, single tone-pulses of high intensity 5-10 kHz elicited negative phonotactic steering; low intensity ultrasound (20-100 kHz) produced only negative phonotactic steering, regardless of pulse repetition pattern. 'Evasive', side-to-side steering, similar to the 'last-chance' bat-evasion behavior of moths was produced in response to high intensity (greater than 90 dB) ultrasound (20-100 kHz). Since the demonstration of negative phonotactic steering did not require the use of a calling song temporal pattern, avoidance of ultrasound cannot be the result of systematic errors in localizing an inherently attractive stimulus when presented at high carrier frequencies. Unlike attraction to model calling song, the ultrasound-mediated steering responses were of short latency (25-35 ms) and were produced in an open loop manner (Fig. 4), both properties of escape behaviors.(ABSTRACT TRUNCATED AT 400 WORDS)