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T Geisel

Publications and source records attributed to T Geisel.

43 records · Page 3Linked to original sources
PubMed1988

Tissue reaction following endobronchial application of iopamidol and ioxithalamate in rats.

Lung tissue reaction to endobronchial application of iopamidol and ioxithalamate were compared by chest radiograph and histological examination in the rat. Radiographs cleared within hours in both groups. Tissue reaction after ioxithalamate application was significantly more pronounced than with iopamidol and included macrophage response, partial atelectasis, and intra-alveolar and interstitial oedema. Different from iopamidol, ioxithalamate induced a significantly stronger reaction than tracheotomy alone. Because no important significant side effects were observed on chest radiographs or in lung histology, iopamidol is recommended for the radiological examination of the gastrointestinal tract in patients with an increased risk of aspiration.

Animals↗
PubMedDate not supplied

Universality in visual cortical pattern formation.

During ontogenetic development, the visual cortical circuitry is remodeled by activity-dependent mechanisms of synaptic plasticity. From a dynamical systems perspective this is a process of dynamic pattern formation. The emerging cortical network supports functional activity patterns that are used to guide the further improvement of the network's structure. In this picture, spontaneous symmetry breaking in the developmental dynamics of the cortical network underlies the emergence of cortical selectivities such as orientation preference. Here universal properties of this process depending only on basic biological symmetries of the cortical network are analyzed. In particular, we discuss the description of the development of orientation preference columns in terms of a dynamics of abstract order parameter fields, connect this description to the theory of Gaussian random fields, and show how the theory of Gaussian random fields can be used to obtain quantitative information on the generation and motion of pinwheels, in the two dimensional pattern of visual cortical orientation columns.

Animals↗
PubMedDate not supplied

How can squint change the spacing of ocular dominance columns?

The pattern of ocular dominance columns in primary visual cortex of mammals such as cats and macaque monkeys arises during development by the activity-dependent refinement of thalamocortical connections. Manipulating visual experience in kittens by the induction of squint leads to the emergence of ocular dominance columns with a larger size and larger column-to-column spacing than in normally raised animals. The mechanism underlying this phenomenon is presently unknown. Theory suggests that experience cannot influence the spacing of columns if the development proceeds through purely Hebbian mechanisms. Here we study a developmental model in which Hebbian mechanisms are complemented by activity-dependent regulation of the total strength of afferent synapses converging onto a cortical neurone. We show that this model implies an influence of visual experience on the spacing of ocular dominance columns and provides a conceptually simple explanation for the emergence of larger sized columns in squinting animals. Assuming that during development cortical neurones become active in local groups, which we call co-activated cortical domains (CCDs), ocular dominance segregation is controlled by the size of these groups: (1) Size and spacing of ocular dominance columns are proportional to the size sigma of CCDs. (2) There is a critical size sigma* of CCDs such that ocular dominance columns form if sigma sigma*. This critical size of CCDs is determined by the correlation functions of activity patterns in the two eyes and specifies the influence of experience on ocular dominance segregation. We show that sigma* is larger with squint than with normal visual experience. Since experimental evidence indicates that the size of CCDs decreases during development, ocular dominance columns are predicted to form earlier and with a larger spacing in squinters compared to normal animals.

Animals↗