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Biomedical subjects

D Lehmann

Publications and source records attributed to D Lehmann.

At least 235 records · Page 13Linked to original sources
PubMedDate not supplied

Intracerebral dipole sources of EEG FFT power maps.

The described method opens a way to compute intracerebral source localizations of ongoing EEG activity. A sine-cosine diagram of the Fourier-transformed data is constructed for each frequency point, forming a "FFT constellation" of entries. Into the FFT constellation of each diagram, a straight line is fitted which produces the least squared deviation sum between the original entry positions and their orthogonal projections onto that line. The map landscape described by the voltages between the projected positions ("FFT approximation") is the least error compromise landscape of all possible landscapes during the paradigmatic cycle of the given FFT frequency. The map thus constructed can be used in the usual dipole source localization procedures. There is one for each FFT frequency point. The squared forward solution of the fitted dipole source and the squared FFT approximation map are "power maps" which are very similar to the original power map. For an average-reference power map with two peaks, the source tends to lie between the peaks; a power map with one peak might show closely neighboring maximal and minimal potential values in the FFT approximation, indicative of a tangential source close to the surface.

Brain↗
PubMedDate not supplied

An EEG approach to the neurodevelopmental hypothesis of schizophrenia studying schizophrenics, normal controls and adolescents.

Based on an integrative brain model which focuses on memory-driven and EEG state-dependent information processing for the organisation of behaviour, we used the developmental changes of the awake EEG to further investigate the hypothesis that neurodevelopmental abnormalities (deviations in organisation and reorganisation of cortico-cortical connectivity during development) are involved in the pathogenesis of schizophrenia. First-episode, neuroleptic-naive schizophrenics and their matched controls and three age groups of normal adolescents were studied (total: 70 subjects). 19-channel EEG delta-theta, alpha and beta spectral band centroid frequencies during resting (baseline) and after verbal stimuli were used as measure of the level of attained complexity and momentary excitability of the neuronal network (working memory). Schizophrenics compared with all control groups showed lower delta-theta activity centroids and higher alpha and beta activity centroids. Reactivity centroids (centroid after stimulus minus centroid during resting) were used as measure of update of working memory. Schizophrenics showed partial similarities in delta-theta and beta reactivity centroids with the 11-year olds and in alpha reactivity centroids with the 13-year olds. Within the framework of our model, the results suggest multifactorially elicited imbalances in the level of excitability of neuronal networks in schizophrenia, resulting in network activation at dissociated complexity levels, partially regressed and partially prematurely developed. It is hypothesised that activation of age- and/or state-inadequate representations for coping with realities becomes manifest as productive schizophrenic symptoms. Thus, the results support some aspects of the neurodevelopmental hypothesis.

Adaptation, Psychological↗
PubMedDate not supplied

Detection of Streptococcus pneumoniae and Haemophilus influenzae type b antigens in the serum and urine of patients with pneumonia in Papua New Guinea: comparison of latex agglutination and counterimmunoelectrophoresis.

Latex agglutination (LA) was compared with counterimmunoelectrophoresis (CIE) for the diagnosis of pneumonia due to Streptococcus pneumoniae or Haemophilus influenzae type b in children less than 6 years old in Papua New Guinea. Neither LA nor CIE was sufficiently sensitive for the detection of pneumococcal antigens. CIE was superior to LA but had a sensitivity of only 60% (six of 10) in concentrated urine and a specificity of 90% (54 of 60). LA for the detection of H. influenzae type b had a sensitivity of 100% (eight of eight) relative to that of blood culture and a specificity of 99% (112 of 113) when urine diluted fivefold was tested, as compared with a sensitivity of 100% (nine of nine) and a specificity of 92% (56 of 61) in undiluted urine. Undiluted and concentrated urine specimens were unsuitable for LA because of the many false-positive reactions that resulted from nasal carriage of H. influenzae type b and nasal carriage of the cross-reactive S. pneumoniae type 6. CIE for the detection of H. influenzae type b had a sensitivity of only 44% (four of nine) in concentrated urine.

Antigens, Bacterial↗
PubMedDate not supplied

Bacterial colonization of the upper respiratory tract and its association with acute lower respiratory tract infections in Highland children of Papua New Guinea.

Acute lower respiratory tract infection (ALRI) is the major cause of death among children in Papua New Guinea. This longitudinal study reports the bacteriologic findings for children observed in their hamlets. A total of 1,449 nasal swab specimens from 158 children less than 5 years of age who were studied intensively for 18 months were examined. Non-serotypable strains of Haemophilus influenzae were isolated from 91% of specimens, and serotypable strains were isolated from 35% (8% H. influenzae type b) of specimens. All children had acquired Streptococcus pneumoniae by the age of 3 months. The most frequently occurring serotypes of S. pneumoniae were 6, 19, and 23. Children more frequently carried invasive pneumococci during an episode of ALRI than when they were healthy. Also, children more frequently carried serotypable strains of H. influenzae during the 2 weeks preceding an episode of ALRI than when they were healthy. Between-children analyses showed that children who were susceptible to attacks of ALRI and those who were not susceptible had similar rates of carriage of bacteria.

Age Factors↗