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Biomedical subjects

K Donner

Publications and source records attributed to K Donner.

62 records · Page 4Linked to original sources
PubMed1979

[Is enostosis frontalis a disease process? (author's transl)].

2851 radiodiagnostic examinations of the skull made in a psychiatric hospital between 1958 and 1977 were reviewed for enostosis frontalis. Out of 1398 female patients there were 125 cases of enostosis frontalis, whereas out of the 1453 male there were only 5. Hence, in females, this is a frequent condition (9%) and shows no correlation with manifest hormonal disease or any particular neuro-psychiatric disturbance. Enostosis frontalis in females can be considered to be an inconstant secondary sex characteristic. In male patients this condition is extremely rare (0.32%). The case histories of the male patients are reported. Endocrine disturbances, cerebral dysplasia and psychiatric disease in connection with mental retardation seem to be associated with enostosis frontalis in men.

Adult↗
PubMedDate not supplied

Modelling the spatio-temporal modulation response of ganglion cells with difference-of-Gaussians receptive fields: relation to photoreceptor response kinetics.

Difference-of-Gaussians (DOG) models for the receptive fields of retinal ganglion cells accurately predict linear responses to both periodic stimuli (typically moving sinusoidal gratings) and aperiodic stimuli (typically circular fields presented as square-wave pulses). While the relation of spatial organization to retinal anatomy has received considerable attention, temporal characteristics have been only loosely connected to retinal physiology. Here we integrate realistic photoreceptor response waveforms into the DOG model to clarify how far a single set of physiological parameters predict temporal aspects of linear responses to both periodic and aperiodic stimuli. Traditional filter-cascade models provide a useful first-order approximation of the single-photon response in photoreceptors. The absolute time scale of these, plus a time for retinal transmission, here construed as a fixed delay, are obtained from flash/step data. Using these values, we find that the DOG model predicts the main features of both the amplitude and phase response of linear cat ganglion cells to sinusoidal flicker. Where the simplest model formulation fails, it serves to reveal additional mechanisms. Unforeseen facts are the attenuation of low temporal frequencies even in pure center-type responses, and the phase advance of the response relative to the stimulus at low frequencies. Neither can be explained by any experimentally documented cone response waveform, but both would be explained by signal differentiation, e.g. in the retinal transmission pathway, as demonstrated at least in turtle retina.

Animals↗
PubMedDate not supplied

In search of the visual pigment template.

Absorbance spectra were recorded by microspectrophotometry from 39 different rod and cone types representing amphibians. reptiles, and fishes, with A1- or A2-based visual pigments and lambdamax ranging from 357 to 620 nm. The purpose was to investigate accuracy limits of putative universal templates for visual pigment absorbance spectra, and if possible to amend the templates to overcome the limitations. It was found that (1) the absorbance spectrum of frog rhodopsin extract very precisely parallels that of rod outer segments from the same individual, with only a slight hypsochromic shift in lambdamax, hence templates based on extracts are valid for absorbance in situ: (2) a template based on the bovine rhodopsin extract data of Partridge and De Grip (1991) describes the absorbance of amphibian rod outer segments excellently, contrary to recent electrophysiological results; (3) the lambdamax/lambda invariance of spectral shape fails for A1 pigments with small lambdamax and for A2 pigments with large lambdamax, but the deviations are systematic and can be readily incorporated into, for example, the Lamb (1995) template. We thus propose modified templates for the main "alpha-band" of A1 and A2 pigments and show that these describe both absorbance and spectral sensitivities of photoreceptors over the whole range of lambdamax. Subtraction of the alpha-band from the full absorbance spectrum leaves a "beta-band" described by a lambdamax-dependent Gaussian. We conclude that the idea of universal templates (one for A1- and one for A2-based visual pigments) remains valid and useful at the present level of accuracy of data on photoreceptor absorbance and sensitivity. The sum of our expressions for the alpha- and beta-band gives a good description for visual pigment spectra with lambdamax > 350 nm.

Animals↗
PubMedDate not supplied

Noise-equivalent and signal-equivalent visual summation of quantal events in space and time.

Noise recorded in visual neurons, or variability in psychophysical experiments, may be quantified in terms of quantal fluctuations from an "equivalent" steady illumination. The conversion requires assumptions concerning how photon signals are pooled in space and time, i.e. how to pass from light fluxes to numbers of photon events relevant to the Poisson statistics describing signal/noise. It is usual to approximate real weighting profiles for the integration of photon events in space and time (the sensitivity distribution of the receptive field [RF] and the waveform of the impulse response [IR]) by sharp-bordered apertures of "complete," equal-weight summation of events. Apertures based on signal-equivalence cannot provide noise-equivalence, however, because greater numbers of events summed with smaller weights (as in reality) have lower variances than smaller numbers summed with full weight. Thus sharp-bordered apertures are necessarily smaller if defined for noise- than for signal-equivalence. We here consider the difference for some commonly encountered RF and IR profiles. Summation areas, expressed as numbers of photoreceptors (cones or rods) contributing with equal weight, are denoted NS for signal and NN for noise; sharply delimited summation times are correspondingly denoted tS and tN. We show that the relation in space is NN = 0.5 NS for the Gaussian distribution (e.g. for the RF center mechanism of retinal ganglion cells). For a photoreceptor in an electrically coupled network the difference is even larger, e.g., for rods in the toad retina NN = 0.2 NS (NS = 13.7 rods and NN = 2.8 rods). In time, the relation is tN approximately 0.7 tS for realistic quantal response waveforms of photoreceptors. The surround input in a difference-of-Gaussians RF may either decrease or increase total noise, depending on the degree of correlation of center and surround noise. We introduce a third useful definition of sharp-bordered summation apertures: one that provides the same signal-to-noise ratio (SNR) for large-long stimuli as the real integration profiles. The SNR-equivalent summation area is N* = N2S/NN and summation time t* = t2S/tN.

Animals↗
PubMedDate not supplied

Refined localisation of the genes for nebulin and titin on chromosome 2q allows the assignment of nebulin as a candidate gene for autosomal recessive nemaline myopathy.

A locus for autosomal recessive nemaline myopathy (NEM2) has been assigned by linkage analysis to a 13-cM region between the markers D2S150 and D2S142 on 2q21.2-q22. The genes for the giant muscle proteins nebulin and titin have previously been assigned by FISH to 2q24.1-q24.2 and 2q31, respectively. By using radiation hybrid mapping, we have reassigned the nebulin gene close to the microsatellite marker D2S2236 on 2q22 and the titin gene to the vicinity of the markers D2S384 and D2S364 on 2q24.3. The genomic orientation of the nebulin gene was determined as 5'-3' and of TTN as 3'-5' from the centromere. We conclude that the nebulin gene resides within the candidate region for NEM2 on the long arm of chromosome 2, while the titin gene is located outside this region.

Chromosome Mapping↗