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Biomedical subjects

G Ehret

Publications and source records attributed to G Ehret.

At least 55 records · Page 3Linked to original sources
PubMed1984

Noise masking of tone responses and critical ratios in single units of the mouse cochlear nerve and cochlear nucleus.

Responses of single units in the cochlear nerve and cochlear nucleus to tone bursts in a background of continuous white broadband noise were recorded. Tone and noise intensities ranged from threshold to saturation levels. Masking of the tone response by the noise was demonstrated by comparing peristimulus-time histograms and spike rates recorded during the tone and between tone presentations. The response of a unit to masking was found to be predictable based upon the difference in its rate of response to the tone and to the noise when the tone was masked. Several nonlinearities of the masking process are described. The most prominent one is an increase in the difference between tone and noise levels at the threshold of masking with increasing tone levels, i.e. neural critical ratios increase with increasing tone level. On the average, the frequency dependence of single unit effective bandwidths and of critical ratio bandwidths is similar to that of mean behavioral critical ratio bands.

Action Potentials↗
PubMed1984

Localization of tones and noise in the horizontal plane by unrestrained house mice (Mus musculus).

House mice (Mus musculus, outbred strain NMRI) were trained to locate loudspeakers at the margin of a wire-mesh covered circular platform. Sound signals were tone bursts of 1, 15, 50 and 80 kHz and noise bursts (bandwidth 15-80 kHz). Localization acuity as represented by orientation angles (alpha) toward the speaker was determined at 5 radial distances from the centre of the platform. If the animals could localize under closed-loop conditions (with repetitive stimulation), the distributions of (alpha) showed a significant peak at the speaker position (0 degrees) and mean orientation angles (alpha) for the different stimuli all varied around 0 degrees. Distributions of (alpha) from open-loop tests were not peaked, i.e. mice did not localize the sound source. We calculated the median angle (beta) of the distributions of orientated runs and used (beta) as a measure for the accuracy of localization. Smallest values of beta were 12 degrees for 1 kHz, 15 degrees for 15 kHz, 9.5 degrees for 50 kHz, 8.5 degrees for 80 kHz tone bursts and 7 degrees for the noise bursts. The results are discussed in relation to possible localization mechanisms in mice.

Animals↗
PubMed1983

Two-tone suppression in auditory nerve fibers of the green treefrog (Hyla cinerea).

The phenomenon of two-tone suppression was studied quantitatively in the peripheral auditory system of the green treefrog (Hyla cinerea). Linear relationships were found between best excitatory and best suppressor frequency, between response thresholds at these frequencies, between Q 10dB-values of excitatory and suppressor tuning curves and best excitatory frequency, and between both Q 10dB-values.

Animals↗
PubMed1981

Postnatal development of absolute auditory thresholds in kittens.

Postnatal development of absolute auditory thresholds in the kitten was behaviorally measured from birth up to 1 mo of age. Unconditioned reactions to pure tones were observed for kittens up to Day 12, and conditioned responses were used for animals from Day 10 onward. At 1 day after birth, the first noticeable responses were obtained in 4 of 11 kittens at frequencies of .5-2 kHZ. At 2 days of age, 12 of 16 kittens responded. Thresholds remained high (above 100 dB SPL) up to the sixth day, but the range of behaviorally effective frequencies extended from .2 to 6 kHZ. All conditioned response thresholds at Day 10 and most at Day 12 were significantly lower than those measured by unconditioned reactions. From 10 days onward, all threshold curves showed a characteristic sensitivity optimum at 4 kHZ. For frequencies below 1 kHZ, maximum sensitivity was reached at Day 15; for frequencies up to 20 kHZ, at Day 20; and for even higher frequencies, at Day 30. At 1 mo of age, the frequency range is adultlike. The present behavioral results on developing acoustic function in the kitten closely followed structural maturation of the acoustic pathway and demonstrated limitations of the ability for acoustical communication during the first week of life.

Aging↗
PubMed1979

Quantitative analysis of nerve fibre densities in the cochlea of the house mouse (Mus musculus).

Transverse sections of the cochlear nerve, silver-stained surface preparations of the cochlea, and silver- and osmium-stained tangential sections of the cochlea of the house mouse were made to determine the number and density of nerve fibres entering the organ of Corti and their distribution to inner and outer hair cells along the cochlear spiral. A number of 12,578 +/- 819 fibres was counted within the cochlear nerve, which is almost equal to the total number of 12,350 +/- 810 fibres entering the organ of Corti. The 12,350 fibres divide into 9,780 (= 79%) fibres running to the inner hair cells, 703 (= 6%) basilar (afferent) fibres and 1,867 (= 15%) upper tunnel radial (efferent) fibres innervating the outer hair cells. About 93% of all afferent fibres are connected to the inner hair cells, and only 7% innervate outer hair cells. The density of fibres running to the inner hair cells varies considerably and has a significant (p less than 0.01) absolute and relative maximum 3.7 mm and 2.9 mm from the apex respectively (total length: 6.84 mm) and decreases toward apex and base. The density of afferent fibres running to the outer hair cells shows a slow increase up to 2 mm from the apex, and remains on a constant low level (5.5 fibres per 40 micrometer) down to the base. The density of efferent fibres running to the outer hair cells increases linearly up to about 2 mm from the apex, remains rather constant (10 fibres per 40 micrometer) from 2 mm to 4 mm, and then decreases toward the base. Generally, the outer hair cells show a convergent innervation pattern, the inner hair cells a divergent one. The significance of the present measurements is discussed in relation to respecitve results from other mammals and in relation to auditory thresholds.

Animals↗
PubMed1978

Stiffness gradient along the basilar membrane as a basis for spatial frequency analysis within the cochlea.

Stiffness z of the basilar membrane of the house mouse against a displacement by sound was calculated from data on width and thickness of the membrane. Three functions of the kind log10z = ax + b were obtained which equally express the stiffness change in dependence on the locus x on the basilar membrane. These functions were compared with the one for frequency representation. The result is that the spatial distribution of displacement maxima for frequencies and of stiffness follows the same kind of place-dependent functions over a large portion of the basilar membrane. From this it can be concluded empirically that the frequency and stiffness (calculated from width and thickness of the basilar membrane) scales along the cochlea are generally proportional to each other and that stiffness is a dominant factor for the determination of the locus of the displacement maximum for a given frequency.

Acoustic Stimulation↗
PubMed1977

Comparative psychoacoustics: perspectives of peripheral sound analysis in mammals.

Psychophysical data on hearing in mammals are summarized. The data are then correlated to the anatomy and physiology of the ear. Common mechanisms of sound transfer and analysis in the acoustic system, with stress on the auditory periphery, are discussed. In this paper an attempt is made to bring basic psychoacoustic data from man and mammals in a logical line with the anatomy, physiology, and biophysics of the ear. This comparative approach is based on man and those five mammals, including bat and dolphin, for which sufficient data are available.

Animals↗
PubMed1975

[Radioimmunological estimation of triiodothyronine in plasma. Diagnostic value in an area with endemic goitre (author's transl)].

In 896 patients from a low-iodine area the results of the radioimmununological triiodothyronine estimations in plasma were compared with the clinical and radioisotope findings of thyroid function. It was superior to the total thyroxine estimation (T4-test) in the differential diagnosis of hyperthyroidism. In euthyroid goitre the mean triiodothyronine concentration was significantly higher than in normal persons whereas the plasma thyroxine levels at the same time were significantly lower. Only in (primary) hypothyroidism is the triiodothyronine estimation diagnostically less important than the T4-test. In summary, the radioimmunochemical method permits a clearly more precise evaluation of thyroid function even in areas of endemic goitre.

Adolescent↗
PubMedDate not supplied

Complex sound analysis (frequency resolution, filtering and spectral integration) by single units of the inferior colliculus of the cat.

The central nucleus of the inferior colliculus (ICC) is a center of convergence of brainstem input and is critical for auditory information processing. Here, the analysis of complex sound spectra by single neurons in the ICC is investigated. Several measures of frequency resolution (excitatory/inhibitory tuning curves, effective bandwidths, critical ratio bands, critical bands derived using narrowband masking and two-tone separation paradigms) have been obtained from the responses of these neurons at sound pressure levels (SPL) up to 80 dB above the units' response thresholds (nearly 110 dB SPL). Among our results are the following: (1) Narrowband masking measures of critical bands from ICC neurons closely parallel behavioral measures using the same stimulus paradigm. (2) Frequency resolution power as measured by critical bandwidths varies little as a function of stimulus intensity. (3) Tuning curves of ICC neurons provide no simple basis for predicting the frequency filtering of the same neurons excited by complex sound spectra. (4) There is a frequency dependence of all measures of frequency resolution similar to that found in psychophysical determinations of critical bandwidths. That is, spatial frequency resolution in the cochlea is the origin for the resolution found in the ICC and in behavioral tests. (5) Lateral inhibition at the level of the ICC clearly plays a role in frequency resolution. (6) Frequency resolution is encoded by response rate changes of ICC neurons and is independent of tone response threshold, response latency, spontaneous activity, tone response type, binaural response type. It is concluded that spectral analysis of sound is established by processes, including lateral inhibition, independent of other basic response properties of neurons at the level of the ICC.

Acoustic Stimulation↗
PubMedDate not supplied

Left hemisphere advantage in the mouse brain for recognizing ultrasonic communication calls.

In humans, sound perceived as speech is processed preferentially by the right ear and the left hemisphere of the brain. Among animals, such an advantage of one hemisphere (lateralization) in processing communication sound from other members of the species has so far been demonstrated only in macaque monkeys. I report here that in the house mouse, which has a very much less elaborate forebrain than man or macaque monkey, the ultrasonic calls that are emitted by young mice to evoke maternal caring behavior are preferentially recognized by the left hemisphere. In females with no experience of pups, which have been trained to respond to the same ultrasonic calls by conditioning, no advantage for one hemisphere is detected. The results suggest that lateralization of this function evolved early in mammals and emphasize that an innate predisposition for perceiving communication sounds is connected with a left-hemisphere advantage in processing them. This experimental system is a readily-available animal model for studying lateralized auditory brain functions.

Animals↗
PubMedDate not supplied

Correlations between cochlear hair cell loss and shifts of masked and absolute behavioral auditory thresholds in the house mouse.

Masked and absolute behavioral auditory thresholds were measured in kanamycin-treated C3H mice with a significant damage or loss of outer hair cells (OHCs) near the cochlear base, and in 17--24-month-old NMRI mice with a significant loss of OHCs and inner hair cells (IHCs) in the basal region and of OHCs near the apex. A loss of IHCs is correlated with an increase in absolute thresholds. A moderate damage or loss of OHCs in a cochlear region had no effect on absolute thresholds but correlated with a decrease and other changes of characteristics of masked thresholds in the respective frequency regions. OH C-damage makes masking by continuous white broad-band noise less efficient. It is concluded that masking and critical bands depend on the function of OHCs, which must be assumed to influence intracochlearly the activity of IHCs in processing the information to the brain.

Animals↗
PubMedDate not supplied

Normal brainstem auditory evoked potentials in Pax5-deficient mice despite morphologic alterations in the auditory midbrain region.

The inferior colliculus in the auditory midbrain region is underdeveloped near the midline in mice lacking the transcription factor Pax5. We have now tested whether hearing deficiencies occur in these mice by measuring auditory evoked brainstem responses. However, the responses and audiograms obtained in homozygous Pax5 mutants did not differ from those of control mice, suggesting that the observed morphologic alterations of the inferior colliculus do not affect hearing, as judged by auditory evoked potential recordings. The only detectable effect of the Pax5 mutation was a delay in the development of the auditory sensitivity and response latency that correlates with the general growth retardation observed in these mice.

Age Factors↗