Three-dimensional reconstruction of the cochlea and temporal bone.
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Cadaver↗
Biomedical subjects
H L Seldon
Publications and source records attributed to H L Seldon.
Effect of chronic electrical stimulation on cochlear nucleus neuron size in normal hearing kittens.
Very young cochlear-implant candidates may have undetected islands of residual hearing. Would the maturation of these functioning auditory neurons be affected by chronic cochlear stimulation? This was tested by examining neuron sizes in the cochlear nuclei of young, normal hearing kittens with and without chronic cochlear stimulation. Six animals received bilateral intra- or extracochlear implants and were electrically stimulated unilaterally for periods of 1,000-1,500 hours. After sacrifice, cross-sectional areas of approximately 11,000 neurons somata in the cochlear nuclei were measured with an image-analysis system. There were statistically significant differences between stimulated and unstimulated nuclei, especially the posteroventral cochlear nucleus (PVCN), in individual cats, but the directions of the differences were inconsistent. Overall, there was no significant effect of electrical stimulation on soma size. These results indicate that chronic electrical stimulation of the auditory nerve has no positive or negative trophic effects on otherwise innervated, maturing cochlear nucleus neurons.
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Cochlear pathology following chronic electrical stimulation of the auditory nerve. I: Normal hearing kittens.
The present study examines the histopathological effects of long-term intracochlear electrical stimulation in young normal hearing animals. Eight-week old kittens were implanted with scala tympani electrode arrays and stimulated for periods of up to 1500 h using charge balanced biphasic current pulses at charge densities in the range 21-52 microC cm-2 geom. per phase. Both click and electrically evoked auditory brainstem responses were periodically recorded to monitor the status of the hair cell and spiral ganglion cell populations. In addition, the impedance of the stimulating electrodes was measured daily to monitor their electrical characteristics during chronic implantation. Histopathological examination of the cochleas showed no evidence of stimulus induced damage to cochlear structures when compared with implanted, unstimulated control cochleas. Indeed, there was no statistically significant difference in the ganglion cell density adjacent to the stimulating electrodes when compared with a similar population in implanted control cochleas. In addition, hair cell loss, which was restricted to regions adjacent to the electrode array, was not influenced by the degree of electrical stimulation. These histopathological findings were consistent with the evoked potential recordings. Finally, electrode impedance data correlated well with the degree of tissue growth observed within the scala tympani. The present findings indicate that the young mammalian cochlea is no more susceptible to cochlear pathology following chronic implantation and electrical stimulation than is the adult.
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Human cochlear nucleus: comparison of Nissl-stained neurons from deaf and hearing patients.
In this study of the effects of deafness on the morphology of the human cochlear nuclei, non-parametric statistical analysis is used to quantify differences in sizes and shapes of neuron somata. Data on 81,007 neuron somata from 11 patients are presented, as well as the total volume and surface area of the cochlear nuclei. Soma size of deaf patients, especially postlinguistically deaf ones, was smaller than that of controls, but not significantly so; the same was true for total cochlear nucleus volume. The data also indicate a greater soma size on the right side (as well as a greater ventral cochlear nucleus volume), a caudal-to-rostral decrease in soma size, and a correlation between soma size and shape. The data base is being continually extended and in future will allow comparisons with measurements from patients suffering from various forms of hearing loss.
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Three-dimensional reconstruction of temporal bone from computed tomographic scans on a personal computer.
The advantages of computer reconstruction of anatomical structures from computed tomographic scans are common knowledge by now. Unfortunately, to date most reconstructions have required the use of large computers and/or have entailed tedious manual contour tracing. The system described here allows largely automatic detection of surfaces in computed tomographic scans plus the usual display capabilities including feature selection, magnification, rotation, shading, and slicing as well as measurement of lengths and angles. It runs on a normal International Business Machines AT-compatible computer with a medium-resolution video card.
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Electrical stimulation of the auditory nerve in deaf kittens: effects on cochlear nucleus morphology.
The present study examines the effects of long-term electrical stimulation of the auditory nerve on the morphology of neurons in the cochlear nucleus in young, sensorineural deaf animals. Kittens, systemically deafened using kanamycin and ethacrynic acid, received bilateral cochlear implants and were stimulated unilaterally for periods of up to four months. After sacrifice, cross-sectional areas of neuron somata were measured with an image-analysis system and compared using nonparametric statistics. The areas of cell somata within the anteroventral cochlear nucleus (AVCN) on the stimulated side were significantly larger than those of corresponding somata on the control, unstimulated side (P less than 0.001). However, there was no statistically significant difference among dorsal cochlear nucleus (DCN) neurons. These results indicate that long-term electrical stimulation of the auditory nerve can at least partially negate some effects of early postnatal auditory deprivation at the level of the cochlear nucleus.
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Tangential preferential orientations of neuron processes in the rat neocortex.
The orientations in the tangential plane, i.e., parallel to the pial surface, of dendrites and axons in several functionally different areas of the rat neocortex were investigated. Using a large data base of over 30,000 measurements and the t-test and chi 2 test for significance, we found an overall preference of both dendrites and axons for the anteroposterior and adjacent orientations. The degree of preference varied from area to area and among different cortical laminae. Other variations were correlated with neuron type and dendritic rank (in a tree). The pyramidal cell dendritic fields show little orientation in the tangential plane, whereas a large fraction of the stellate cells are oriented. The overall preferential orientations are apparently related to brain axes and growth lines, whereas the variability is probably due to the influence of the functional topography.
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Structure of human auditory cortex. III. Statistical analysis of dendritic trees.
3-Dimensional coordinates of Golgi-impregnated neurons in left and right human areas TA, TB and TC were stored using computer microscopy. The tangential extent of neurons was taken to be an estimate of their effective radius, which is a compromise between their maximum radius and the average tangential projection of their dendrites. Analysis of variance and t-test comparisons were made among the areas and between the hemispheres on a total data base of 622 neurons. It was assumed that the neurons are organized in functional columns. The tangential extent of left-hemisphere columns is absolutely larger than on the right, but is smaller relative to the column-column interval. Neuropil on the left is packed more densely with dendrites belonging to the nearest column. It seems that during the course of evolution interconnected units (as in the right hemisphere) have become more disentangled (left hemisphere), yielding perhaps a greater capacity for differentiated responses in the latter case. A more detailed analysis revealed that much of the difference between areas and/or hemispheres was due to the pyramidal neurons. The structure of non-pyramidal cells is relatively consistent within each hemisphere and shows non-systematic differences between the hemispheres.
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Structure of human auditory cortex. I. Cytoarchitectonics and dendritic distributions.
In the human primary and secondary auditory cortices the neuron somata are arranged in distinct columnar clusters. Measurements on their diameters and the intervals between them yield significant hemispherical differences, having in all cases greater values in the left hemisphere. Computer-assisted tracings of Golgi-impregnated dendritic trees of 300 neurons show the expected types. An analysis of the columnar structure of the dendritic trees indicates varying degrees of specificity in collecting information from their surroundings. An analysis of their tangential extent shows that in the primary cortices a greater extent in the left hemisphere effectively cancels the differences in columnar widths and intervals, allowing for a similar dendritic connectivity among columns in both hemispheres. In the secondary cortex this connectivity is greater on the right side.
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Structure of human auditory cortex. II. Axon distributions and morphological correlates of speech perception.
In Golgi-impregnated specimens of human auditory cortex banding patterns of cortical afferents have been found. Viewed sagitally they are vertical columns with components in layers III, IV, VI and sometimes V. Viewed tangentially they are winding stripes roughly parallel to the gyral axis and of variable width (usually a few hundred micrometers). Although it is not possible to determine it in such sections, they are probably - by analogy with animal experiments - of callosal and/or thalamic origin. Also found were narrow radial bundles, also of indefinite origin. Relative densities of impregnated axons were higher in the columns than between them; also, the tangential orientation component was accentuated within the columns. These findings, together with those of the previous paper, are related to neurolinguistic discoveries. Possible morphological correlates are discussed for neurolinguistic phenomena such as parallel processing of phonemes and words and unilateral, categorical perception of consonants compared with bilateral recognition of vowels and continuous transitions between them.
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Preferential orientations of nerve processes in cat and monkey cortex.
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Animals↗