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P J Kolston

Publications and source records attributed to P J Kolston.

9 recordsLinked to original sources
PubMed2000

The importance of phase data and model dimensionality to cochlear mechanics.

The vulnerability of the mammalian cochlear amplifier to surgical trauma hinders observations of its behaviour in vivo. This produces a greater need for realistic models to aid the interpretation of the experimental observations. The emphasis in most modelling studies has been to simulate the gain of the response of the basilar membrane. This paper argues that matching the phase behaviour of the response should be given at least equal importance. When it is, many of the models used to justify hypotheses regarding the operation of the cochlear amplifier cannot simulate the response even of the dead cochlea. This discrepancy is due to oversimplification of the mechanics of the cochlear fluids. It is argued that three-dimensional fluid behaviour should be regarded as a bare minimum in any quantitative description of cochlear mechanics. Furthermore, it is shown that a three-dimensional model is consistent with experimental data from a healthy cochlea only when the main effect of the cochlear amplifier is to inject mechanical energy into the basilar membrane. The injection of mechanical energy is fundamentally different to modifying the stiffness of the basilar membrane. This means that existing models which possess cochlear amplifiers that effect large changes on the stiffness of the basilar membrane may not be accurate representations of the real organ.

Animals↗
PubMed1999

Comparing in vitro, in situ, and in vivo experimental data in a three-dimensional model of mammalian cochlear mechanics.

Normal mammalian hearing is refined by amplification of the motion of the cochlear partition. This partition, comprising the organ of Corti sandwiched between the basilar and tectorial membranes, contains the outer hair cells that are thought to drive this amplification process. Force generation by outer hair cells has been studied extensively in vitro and in situ, but, to understand cochlear amplification fully, it is necessary to characterize the role played by each of the components of the cochlear partition in vivo. Observations of cochlear partition motion in vivo are severely restricted by its inaccessibility and sensitivity to surgical trauma, so, for the present study, a computer model has been used to simulate the operation of the cochlea under different experimental conditions. In this model, which uniquely retains much of the three-dimensional complexity of the real cochlea, the motions of the basilar and tectorial membranes are fundamentally different during in situ- and in vivo-like conditions. Furthermore, enhanced outer hair cell force generation in vitro leads paradoxically to a decrease in the gain of the cochlear amplifier during sound stimulation to the model in vivo. These results suggest that it is not possible to extrapolate directly from experimental observations made in vitro and in situ to the normal operation of the intact organ in vivo.

Acetylcholine↗
PubMed1996

Finite element micromechanical modeling of the cochlea in three dimensions.

A new cochlear modeling technique has been developed in which the number of assumptions required in model formulation is significantly less than in previous modeling studies. The main new feature of the method is that it allows individual cellular and membrane components of the organ of Corti to be embedded within the model fluid in their true structural positions, with connections to neighboring elements reflecting anatomical geometry. The cochlea is divided into a three-dimensional finite element (3-D FE) network of nodes, connected by branches representing the local mechanical properties. The model system of simultaneous equations, obtained by applying continuity at each node, is solved iteratively using a variant of the conjugate gradient method. Here the formulation and implementation of the 3-D FE method are described. Force generation by outer hair cells is included and results are presented which demonstrate the effect of tectorial membrane and Deiters' cell mechanical properties on the effectiveness of the cochlear amplifier.

Animals↗
PubMed1994

Hair cell based amplification in the cochlea.

Recently, several reports have provided data about the way in which outer hair cells amplify sound within the cochlea. These include new measurements of hair cell forces in the cochlea and in isolated hair cells. In addition, theoretical advances that synthesize such experiments and show how hair cells might tune up the cochlear response sound promising.

Animals↗
PubMed1993

GABAB-mediated modulation of ionic conductances in type I hair cells isolated from guinea-pig semicircular canals.

Mammalian vestibular type I hair cells (VIHCs) are innervated by an afferent synaptic calyx which contains vesicles and is immunoreactive for GABA. We describe here the effects of GABA on electrophysiological properties and on cytosolic free-calcium levels ([Ca2+]i) of VIHCs isolated from guinea-pig ampullae. Whole-cell tight-seal macroscopic currents recorded from VIHCs showed that 100 microM GABA induced a decrease in the outward currents elicited by depolarizing membrane potentials. These are known to comprise potassium calcium-dependent currents. This effect was mimicked by baclofen, a GABAB agonist, and was not affected by picrotoxin, a GABAA antagonist. GABA also induced an increase in the inward current elicited at hyperpolarized membrane potentials in 50% of the tested cells. Single channel recording in cell-attached patches revealed that externally applied GABA produced a decrease and an increase in the open probability of 170 pS and 45 pS and of 15 pS channels, respectively. In imaging experiments using the dye Fura-2 to measure [Ca2+]i, the only reversible modulation of [Ca2+]i observed in response to GABA application was a decrease. These results demonstrate a modulation of calcium and potassium conductances by GABA, via GABAB receptors, in guinea-pig VIHCs.

Animals↗
PubMed1990

What type of force does the cochlear amplifier produce?

Recent experimental measurements suggest that the mechanical displacement of the basilar membrane (BM) near threshold in a viable mammalian cochlea is greater than 10(-8) cm, for a stimulus sound-pressure level at the eardrum of 20 microPa. The associated response peak is very sensitive to the physiological condition of the cochlea. In the formulation of all recent cochlear models, it has been explicitly assumed that this peak is produced by the cochlear amplifier injecting a large amount of energy into the cochlea, thereby altering the real component of the BM impedance. In this paper, a new cochlear model is described which produces a realistic response by assuming that the cochlear amplifier force acts at a phase such that the main effect is to reduce the imaginary component of the BM impedance. In this new model, the magnitude of the cochlear amplifier force required to produce a realistic response is much smaller than in the previous models. It is suggested that future experimental investigations should attempt to determine both the magnitude and the phase of the forces associated with the cochlear amplifier.

Acoustic Impedance Tests↗
PubMed1989

Realistic mechanical tuning in a micromechanical cochlear model.

Two assumptions were made in the formulation of a recent cochlear model [P.J. Kolston, J. Acoust. Soc. Am. 83, 1481-1487 (1988)]: (1) The basilar membrane has two radial modes of vibration, corresponding to division into its arcuate and pectinate zones; and (2) the impedance of the outer hair cells (OHCs) greatly modifies the mechanics of the arcuate zone. Both of these assumptions are strongly supported by cochlear anatomy. This paper presents a revised version of the outer hair cell, arcuate-pectinate (OHCAP) model, which is an improvement over the original model in two important ways: First, a model for the OHCs is included so that the OHC impedance is no longer prescribed functionally; and, second, the presence of the OHCs enhances the basilar membrane motion, so that the model is now consistent with observed response changes resulting from trauma. The OHCAP model utilizes the unusual spatial arrangement of the OHCs, the Deiters cells, their phalangeal processes, and the pillars of Corti. The OHCs do not add energy to the cochlear partition and hence the OHCAP model is passive. In spite of the absence of active processes, the model exhibits mechanical tuning very similar to those measured by Sellick et al. [Hear. Res. 10, 93-100 (1983)] in the guinea pig cochlea and by Robles et al. [J. Acoust. Soc. Am. 80, 1364-1374 (1986)] in the chinchilla cochlea. Therefore, it appears that mechanical response tuning and response changes resulting from trauma should not be used as justifications for the hypothesis of active processes in the real cochlea.

Animals↗
PubMed1988

Sharp mechanical tuning in a cochlear model without negative damping.

It is possible for a cochlear model without active negative damping to exhibit a mechanical response peak that is arbitrarily high and arbitrarily wide. Conventional active models rely on external energy inputs to the cochlea to produce the required peak shape. The new model proposed here produces very similar response profiles by assuming that outer hair cell stereocilia stiffness suppresses the mechanical motion in all regions basal of the response peak. Therefore, the model is not active in the usual sense of adding energy to the cochlea. The model suggests a reason for the differing basilar membrane structure in the arcuate and pectinate zones and simulates in vivo and postmortem responses similar to those measured in the real cochlea.

Animals↗