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Biomedical subjects

E de Boer

Publications and source records attributed to E de Boer.

At least 91 records · Page 5Linked to original sources
PubMed1987

Cochlear power flux as an indicator of mechanical activity.

The question of whether one can conclude just from basilar membrane (BM) vibration data that the cochlea is an active mechanical system is addressed. To this end, a method is developed which computes the power flux through a channel cross section of a short-wave cochlear model from a given BM vibration pattern. The power flux is an important indicator of mechanical activity because a rise in this function corresponds to creation of mechanical energy. The power flux method is applied to BM velocity patterns as measured by Johnstone and Yates [J. Acoust. Soc. Am. 55, 584-587 (1974)] and by Sellick et al. [Hear. Res. 10, 101-108 (1983)] in the guinea pig and by Robles et al. [Peripheral Auditory Mechanisms, edited by J.B. Allen, J.L. Hall, A.E. Hubbard, S.T. Neely, and A. Tubis (Springer, New York, 1986a), pp. 121-128, and J. Acoust. Soc. Am. 80, 1364-1374 (1986b)] in the chinchilla. Before the calculations are performed, the BM data are interpolated and smoothed in order to avoid numerical errors as a result of too few and noisy data points. The choice of the smoothing method influences the computed power flux function considerably. Nevertheless, the calculations appear to make a clear distinction between the "old" data, showing broad BM tuning (Johnstone and Yates, 1974), and the "new" data, in which the response is much more peaked (Sellick et al., 1983; Robles et al., 1986a, b). The former do not give rise to a significant increase of the power flux; the latter do, although less convincingly for the Sellick et al. (1983) data than for the Robles et al. (1986a,b) data. It is thus concluded that the recently obtained, sharply tuned BM responses reflect the presence of mechanical activity in the cochlea.

Basilar Membrane↗
PubMed1987

Auditory psychophysics: spectrotemporal representation of signals.

The study of audition has widened: Having been concentrated in the 1960s on a few topics like pitch perception, binaural hearing, and fatigue, it now spans many more subjects. In the present paper we have emphasized the following topics: frequency analysis--this topic includes spectral integration and resolution, auditory excitation patterns, and processing of spectral information; temporal analysis--this topic refers mainly to studies in which abstract and stylized temporal variations in stimuli are used; binaural hearing--a subfield that still attracts a great deal of attention because of its unique character; pitch perception--of particular interest is this field for the perception of prosodic features of speech, but it also addresses fundamental questions of how the auditory system works; and pathology of hearing--in particular the effects of impaired hearing on speech perception and the relations among various hearing-test results. (This section was written in collaboration with W. A. Dreschler.) Many of the topics discussed have a direct relation to the capabilities of the auditory system in analyzing sounds--in particular, speech sounds. Experimentally, the problem can be approached from two sides: in one the stimuli are generated in a stylized form, and in the other they are taken as distorted versions of actual speech elements. In this paper we have described mainly the first category of experiments. Whereas we know for certain that the auditory system operates in the frequency-temporal domain, it is remarkable that the distinction between fields 1 and 2 (above) can still be made. Temporal effects in frequency analysis are often considered as perturbations, and the same is true for spectral effects in the study of temporal resolution. A true integration of time and frequency is often sought but seldom achieved as the focus of study. Of the many subjects that would ideally have received more coverage we mention two: the use of additional stimulation pathways to help patients with large hearing loss or deaf-blind people, and the use of a cochlear prosthesis ("cochlear implant"). Because we lacked space to cover these topics adequately, we omitted them completely. This indicates no undervaluation of these subjects of study or of the benefits they can provide to hearing-impaired people.

Auditory Perception↗
PubMed1987

The regulation of expression of human beta-globin genes.

We have analyzed the regulation of expression of the human beta-globin gene by DNA mediated gene transfer in MEL cells and microinjection in fertilized mouse eggs. The results show that the beta-globin gene contains two regulatory elements: one element in the promoter, that is required for full transcriptional activity and, secondly, a tissue and developmental specific enhancer 3' to the gene.

Animals↗
PubMed1986

Time course of suppression.

The time course of suppression was studied by shortening the length of the suppressor tone burst in a forward masking paradigm and observing the decrease in magnitude of the compound action potential. The time course was found to be slower than expected on the basis of peripheral filtering.

Acoustic Stimulation↗
PubMed1986

Forward and reverse waves in the one-dimensional model of the cochlea.

Consideration of a source of oto-acoustic emission in a cochlear model implies consideration of the types of waves that such a source can emit. One wave travels in the normal, forward, direction. As any other forward wave it undergoes little or no reflection and it eventually disappears completely because of dissipation. The other wave travels in the reverse direction and it appears to undergo appreciable reflection. In the present paper this phenomenon is studied via the use of two appropriately simplified long-wave models of the cochlea. One model, the exponential model, puts emphasis on the variation of the stiffness along the length of the basilar membrane. The second model concentrates on what happens in the region of resonance. The latter model turns out to have the largest predictive power for the problem at hand. Consideration of the flow of energy in the cochlear fluid brings forth the explanation why in the used model of the cochlea reflection conditions at the stapes have such a surprisingly small influence on the operating conditions of a potential source of emission.

Basilar Membrane↗
PubMed1986

Are active elements necessary in the basilar membrane impedance?

This article is motivated by the current hypothesis [Kim et al., Psychological, Physiological and Behavioural Studies in Hearing (Delft U. P., The Netherlands, 1980); Neely, Doctoral dissertation, Washington University, St. Louis, MO (1981); de Boer, J. Acoust. Soc. Am. 73, 567-573 (1983a) and 73, 574-576 (1983b)] that it is necessary to include active elements in the basilar membrane (BM) impedance in order to explain recent data on the vibration of the BM [Khanna and Leonard, Science 215, 305-306 (1982); Sellick et al., J. Acoust. Soc. Am. 72, 131-141 (1982); Robles et al., Peripheral Auditory Mechanisms (Springer, New York, 1986)]. In order to test this hypothesis, first, a method which is an inversion of the customary description of cochlear mechanics is described. Instead of computing the BM velocity for a given point impedance of the membrane, we show how to compute the impedance function from a given BM velocity pattern in response to a sinusoidal input at the stapes. This method is then used to study the sensitivity of the recovered impedance to perturbations in the velocity pattern. The simulations used show that the real part of the impedance is extremely sensitive to such perturbations. Therefore, measured velocity patterns are unlikely to resolve the issue of whether active elements should be included. Frequency responses measured at a few points on the membrane are even less likely to do so.

Basilar Membrane↗
PubMed1984

Wave propagation and dispersion in the cochlea.

Insight into cochlear mechanics can be obtained from semi-analytical and asymptotic solution methods of which the Liouville -Green (LG) method - in another context known as the WKB method - is the most important one. This paper describes the dispersion properties of fluid waves in general terms and develops the LG formulation on that basis. The eikonal equation of the LG method is shown to be identical to the dispersion relation in dispersive-wave theory. Consideration of the group velocity then leads to the derivation of the central LG formula as it has been used in an earlier paper on the LG method ( Boer , E. and Viergever , M.A. (1982): Hearing Res. 8, 131-155). The formulation appears to apply as well to dissipative and active (i.e., energy-producing) systems. Of the many possible collateral subjects two are selected for a deeper discussion: amplification, concentration and expansion of energy, and the problem of reflection of cochlear waves. In the latter context, it is shown why - and under which conditions - cochlear waves are not reflected, despite the large degree of dispersion that they show. The analysis brings to light a fundamental asymmetry of the model regarding the direction of wave travel: waves travelling in the direction opposite to the normal one are likely to undergo reflection, while waves in the normal direction are not reflected.

Basilar Membrane↗
PubMed1983

[Campylobacter jejuni, Yersinia enterocolitica and Salmonella in game and poultry].

Samples of various sorts of game and poultry (other than chicken), obtained from poulterers, hunters, rearing-farms and slaughterhouses, were surveyed for the presence of Campylobacter jejuni, Yersinia enterocolitica and Salmonella. These pathogens were isolated from hare, wild boars, pheasants, guinea-fowl, turkeys, mallards and domestic ducks. Yersinia enterocolitica and Salmonella were also cultured from wild and domestic rabbits. Moreover, Yersinia enterocolitica was isolated from wood pigeons. The possible origins of contamination of game and poultry with these pathogenic bacteria and the risks of food-borne infection caused by these products are discussed.

Animal Population Groups↗
PubMed1983

No sharpening? a challenge for cochlear mechanics.

Recent data on mechanical movements of the basilar membrane (BM) suggest that the part played in cochlear physiology by a sharpening mechanism is much less important than hitherto has been thought. In an extreme view, one could dispense with a sharpening mechanism completely and assume that (near the threshold) hair-cell excitation is proportional to BM velocity, or a very simple linear transform of it. In the present paper the consequences of this idea are worked out. A theoretical cochlear movement pattern is constructed that shows the same frequency selectivity as an average reverse-correlation function of an auditory nerve fiber. This response is called a revcor-spectrumlike response. Cochlear mechanics is then simplified to a pure shortwave model. It is shown that, if the cochlea model should present a revcor-spectrumlike response, this can only be achieved when the resistance component of the BM impedance is negative over a part of the length of the cochlea. This result is refined in several respects, and it is shown that a model equipped with the right kind of BM impedance function can have a response of the required type. It remains difficult to conceive of a physiological mechanism that would cause the desired effect on the BM impedance.

Basilar Membrane↗
PubMed1983

On active and passive cochlear models--toward a generalized analysis.

Simple cochlear models can show a peak in their response but only of a limited magnitude. The constraints limiting the size of this peak are studied in this note, for the short-wave as well as the long-wave case. It is found that a sharply rising response is impossible in a model in which the basilar membrane can only absorb acoustical energy. To attain a model response that is comparable to the response found in the most recent experiments, the basilar membrane must be assumed to be capable of adding acoustic energy to the fluid waves.

Basilar Membrane↗
PubMed1983

Power amplification in an active model of the cochlea--short-wave case.

To account for the most recent experimental results on cochlear mechanics, a mathematical model should include an active source of vibrational energy. In this note the energy gain of such a model is computed, for the case that only short waves are supported. It is shown how, via a so-called criterion function, the required energy gain can be found from the basilar-membrane velocity response.

Acoustics↗
PubMed1982

The DNA sequence of the 5' flanking region of the human beta-globin gene: evolutionary conservation and polymorphic differences.

We have determined the DNA sequence of a 1464 bp segment immediately flanking the 5' side of the human beta-globin gene. The sequence shows little similarity to the corresponding regions of the epsilon- or gamma-globin genes. There is about 75% homology, however, between the 5' extragenic regions of the beta-globin genes of man, goat and rabbit respectively. The mouse beta minor globin gene, but not the mouse beta major globin gene, also shares this extensive homology. A short segment of simple sequence DNA is found from about 1418 to 1388 bp upstream from the human beta-globin gene which consists of repeats of the sequence (TTTTA). Similar DNA sequences are also found at several sites in the large intron of the beta-globin gene. We have compared the DNA sequence of the 5' extragenic region of the normal beta-globin gene with the same segment of the beta-globin gene of a patient with beta thalassaemia. Of the two nucleotide differences observed, one generates a polymorphic HinfI site present 990 bp upstream from the beta-globin gene in the thalassaemic beta-globin and absent in the normal gene. A second beta thalassemic beta-globin gene which has the same molecular defect as the above mentioned case, however, lacks this HinfI site. It is therefore not yet clear whether this HinfI site will have any value in prenatal diagnosis of beta thalassaemia.

Animals↗
PubMed1982

DNA sequences necessary for transcription of the rabbit beta-globin gene in vivo.

The DNA sequences required for the expression of the rabbit-beta-globin gene in vivo have been examined. A variety of mutant rabbit beta-globin gene templates were linked to a simian virus 40-plasmid recombinant and introduced into HeLa cells; in these conditions the rabbit beta-globin gene is expressed from its own promoter. Comparison of the level of beta-globin transcripts in a variety of deletion mutants shows that for efficient transcription, both the ATA or Goldberg-Hogness box, and a region between 100 and 58 base pairs in front of the site at which transcription is initiated, are required. Deletion of either of these regions results in a decrease in the level of beta-globin transcripts by an order of magnitude; deletion of the ATA box causes an additional loss in the specificity of the site of initiation of RNA synthesis. The DNA sequences downstream from the ATA box, including the natural beta-globin mRNA cap site, are dispensable for transcription in vivo.

Animals↗
PubMed1982

Validity of the Liouville--Green (or WKB) method for cochlear mechanics.

This article presents a comparison of Liouville-Green (LG) calculations and exact solutions of 2- and 3-dimensional cochlea models. The agreement is in general quite good. For certain choices of the model parameters, however, the 2- and 3-dimensional LG solutions show appreciable errors in the region just beyond the location of maximum amplitude of the basilar membrane response. The origin of these errors appears to be the non-uniqueness of the (complex) LG wave number k(x) in 2- and 3-dimensional models: the 'eikonal equation' from which k(x) has to be solved has multiple roots. To study this problem somewhat deeper, the properties of the locus of k=k(x) formed when x is varied, are investigated. Erratic behaviour of the LG solution is found to occur when this root locus approaches one of the saddle points of a complex function of k- called Q(k)- which plays the major role in the eikonal equation. Apart from this specific problem, the LG approximation is very well suited to unravel the mechanisms governing wave propagation and attenuation in the cochlea. The analysis shows clearly why and how the response of the basilar membrane builds up to a maximum and which factors cause a turnover and a rapid decrease to occur, in both the long-wave and the short-wave cases. A special discussion is dedicated to the relation between the LG approximation and the absence of wave reflection in cochlea models of the type studied.

Acoustics↗
PubMed1982

Correspondence principle in cochlear mechanics.

When only long waves play the most important part in the cochlea, the response can be described by a most simplified model, the one-dimensional model. When short waves are to be included, a more complex model is needed. The response then depends on the dimensionality of the model and is much harder to obtain. This applies especially to the region in the neighborhood of the point where the basilar membrane shows resonance. Both two- and three-dimensional models have been studied to assess the effects of short and long waves. The relative importance of the part played by short waves depends on the damping constant (or loss factor )delta associated with the resonance of the basilar membrane (BM). For very small delta a three-dimensional model is really necessary, it cannot be replaced by a model of lower dimensionality. When delta is small, but not too small, the three-dimensional model can be made equivalent to a two-dimensional one, provided the latter is modified ina specific manner. This paper shows why this is so and which conditions have to be met. The two-dimensional model must undergo two modifications to effect this equivalence. The first modification ensures that the model has the same long-wave behavior. In the second place, a specific additional mass ("added mass") reactance should be added to Z(kappa). An expression for the limiting value of delta, above which this correspondence is valid, is given in the paper. A second, larger, limit is presented as well: when delta is above this limit, the responses of both the three-dimensional and the two-dimensional model are equivalent to that of an appropriately chosen one-dimensional model. In this case too, long-wave behavior must be matched and an "added mass" reactance must be included in Z(kappa). This holds true for the entire cochlea including the region of resonance. For both types of transition the amount of "added mass" is given.

Basilar Membrane↗
PubMed1982

Solving cochlear mechanics problems with higher-order differential equations.

Since most "exact" solution methods for cochlear models are rather unwieldy, they do not lend themselves to easy and multi-purpose application. In this paper a new solution method is described that is more flexible in this respect. A three-dimensional cochlear model is considered. It can be described by an integral equation in terms of the wavenumber k. The kernel Q (k) of that equation is approximated by a rational function of k and this makes it possible to reformulate the problem as a differential equation. The latter can be solved by a straightforward and well-known method. Results of computations with this technique are presented in two forms: an overview of the entire cochlear wave pattern and a detailed representation of the response peak. The method is also used to determine whether a discernible reflected wave is produced in the cochlea or not. For this purpose the wavenumber spectrum of the cochlear wave is studied: it is found to be a one-sided function of k. With surprisingly simple means it is thus shown that no appreciable reflection occurs from the inhomogeneity that is characteristic in cochlear wave propagation. This holds true for values of damping constant delta as low as 0.01, a factor of 5 smaller than is commonly used in cochlear modeling.

Basilar Membrane↗