Jack P. Landolt

Neuromathematical Concepts of Point Process Theory

The mathematical foundations for describing a discrete series of events such as a spike train are presented by way of a point process theoretic approach. Various significance tests and empirical descriptors are discussed. These may be used in fitting a model to spike train data. The application of these techniques to the single unit, spontaneous activity from peripheral semicircular canal units in the pigeon is demonstrated as an example.

Size Distribution Analysis of Myelinated Fibers in the Vestibular Nerve of the Pigeon.

Abstract Nerve fiber counts and the spectral distribution of the myelinated nerve fiber diameters were determined for the vestibular nerve of the White King pigeon. An analysis of variance indicated that the raw data for the utricular, saccular, neglectar, anterior ampullary, and horizontal ampullary nerve branches could be pooled to give an overall unimodal distribution having a mode in the range of 1–2 μm. this could not be done for the posterior ampullary nerve and an intraspecific variation was considered to be the cause of the discrepancy. The utricular nerve had more fibers smaller than 3 μm in diameter (84.9%) than the other branches. Overall, 63.8% of fibers (exclusive of posterior ampullary nerve) were less than 3 μm in diameter. For the individual nerve branches the following average fiber counts ± standard deviations were obtained: 1774 ± 88 for the utricular nerve, 111 ± 243 for the saccular nerve, 86 ± 5 for the neglectar nerve, 1716 ± 142 for the anterior ampullary nerve, 1554 ± 151 for the horizontal ampullary nerve, and 1679 ± 218 for the posterior ampullary nerve. When all branches were combined the average number of fibers was 8720 ± 847 in a diameter range of 1–17 μm.

Semicircular Canal Fractures in Squirrel Monkeys Resulting from Rapid Decompression: Interpretation and Significance

A recent histological study of monkeys rapidly decompressed from deep dives has revealed that, in some cases, there are fractures of the bone surrounding the semicircular canals. In some monkeys sacrificed within a few days of their dives, there are full thickness breaks across the bony canal walls. In others, sacrificed several months after a dive, these fractures have become infiltrated by the ectopic growth of new bone which also invades the otic fluid spaces. It now appears that the new bone growth is caused not only by a ripping or irritation of the endosteum, which lines the inside of the bony canals, but also, at least in some cases, by a rupturing of the very hard petrous bone itself. It is difficult to avoid the conclusion that, somehow, large forces are developed within the inner ear or within the petrous bone during decompression.

Deuterium oxide modification of neuronal characteristics in the visual cortex of the cat.

The receptive field area and the spontaneous activity of complex visual cortical cells were investigated in the cat before, and after, the administration of deuterium oxide (D2O). In cats with intact labyrinths, the receptive field area of the cell usually expands, and the spontaneous activity increases. In bilaterally labyrinthectomized animals, these changes are absent. Also, D2O does not alter the spontaneous firing rate in non-visual cortical cells in normal cats.

Induced Vestibular Dysfunction in Squirrel Monkeys During Rapid Decompression

The symptoms of postural instability and dizziness associated with decompression sickness could be ascribed to either damage of the vestibular apparatus or to central nervous system damage. However, a histological study of monkeys exposed to decompression reveals that these symptoms primarily result from damage to the vestibular apparatus (unless there are accompanying central deficits). Furthermore, the damage is of a type that causes new bone growth to occlude the otic fluid spaces of the semicircular canals. In some instances, there is sufficient bone growth to render the cristae ampullares as non-functional end organs. Such diminished vestibular function would present a serious threat to the diver.

The marginal fiber mass in the utricle of the pigeon

Abstract The marginal fiber mass (MFM) that Werner26 described in the utricle ofAves was observed and analyzed in the pigeon using light, scanning electron, and transmission electron microscopic techniques. Morphologically, the MFM is a gelatinous, fibrous mass which has the shape of an oblique cone. The basal end terminates as a foot-like structure on the macula utriculi while the apical end attaches the statoconial membrane securely to the wall of the utricle. Specific tests for elastin, collagen and a ‘connective tissue type’ of reticulum indicated that none of these components were present in the MFM. The MFM did, however, stain positively with PAS, Alcian blue and a PAS-Alcian blue combination. The extent and location of the staining suggest that the main bulk of the MFM is comprised primarily of neutral mucopolysaccharides with traces of acid mucopolysaccharides on its surfaces. Based on these facts, and on other morphological observations, it is suggested that the MFM is a marginal extension of the cupular zone of the statoconial membrane which has folded back over on itself and, in the process, has sandwiched the statoconial (otolithic7) zone between itself and the cupular zone. As a well-developed structure of the avian utricle, the MFM must be considered as a functional component in any biodynamical model of statoconial membrane displacement.

Cluster analysis of visual cortical responses evoked by moving lines.

The cortical evoked responses to a bar of light (line) moving in 8 different directions across the visual field of 6 unanaesthetized, immobilized cats were compared in 18 experimental sessions. The shape of the response is unique for each direction. This is particularly apparent during the first 350 msec of the response. Cluster analysis of the evoked potentials reveals that the recognition of the direction of the moving line is probably less distinct when the line moves in a downward direction. This finding is more pronounced in the left hemisphere. The results of the cluster analysis indicate that the technique may be a useful tool in the analysis and classification of large numbers of evoked potentials. Furthermore, such clustering may eventually reveal some of the physiological mechanisms that contribute to the shape of the evoked response.