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D Lehmann

Publications and source records attributed to D Lehmann.

At least 73 records · Page 4Linked to original sources
PubMed1997

Chewing-gum flavor affects measures of global complexity of multichannel EEG.

Global complexity of spontaneous brain electric activity was studied before and after chewing gum without flavor and with 2 different flavors. One-minute, 19-channel, eyes-closed electroencephalograms (EEG) were recorded from 20 healthy males before and after using 3 types of chewing gum: regular gum containing sugar and aromatic additives, gum containing 200 mg theanine (a constituent of Japanese green tea), and gum base (no sugar, no aromatic additives); each was chewed for 5 min in randomized sequence. Brain electric activity was assessed through Global Omega (Omega)-Complexity and Global Dimensional Complexity (GDC), quantitative measures of complexity of the trajectory of EEG map series in state space; their differences from pre-chewing data were compared across gum-chewing conditions. Friedman Anova (p < 0.043) showed that effects on Omega-Complexity differed significantly between conditions and differences were maximal between gum base and theanine gum. No differences were found using GDC. Global Omega-Complexity appears to be a sensitive measure for subtle, central effects of chewing gum with and without flavor.

Adult↗
PubMed1997

Influence of oxygen ventilation on Doppler microemboli signals in patients with artificial heart valves.

BACKGROUND AND PURPOSE: The purpose of this study was to evaluate the influence of inhalation of 100% oxygen on microembolic signal (MES) counts in patients with artificial cardiac valves. METHODS: A total of 134 outpatients were examined. Transcranial Doppler baseline monitoring (45-minute duration) was performed in all patients under resting conditions. The first 30 patients subsequently underwent transcranial Doppler monitoring for at least 20 minutes under noninvasive positive pressure ventilation with 100% oxygen and for an additional 30 minutes under resting conditions. The same protocol was applied to all following patients with a baseline MES count > or = 10, while the examination was discontinued in the remaining patients. RESULTS: Baseline MES counts < 10, which remained unchanged during oxygen inhalation and the subsequent resting period, were observed in 26 of 30 initial patients. A total of 46 patients with MES counts > or = 10 were identified. Oxygen application was feasible in 43 patients. An exponential MES decrease was noted in 42 patients during oxygen inhalation (statistically significant in 38 patients), followed by a subsequent increase in 38 of 43 patients (statistically significant in 25 patients) under resting conditions. CONCLUSIONS: The exponential reduction of MES counts observed in this study corresponds to blood denitrogenation, thus strongly arguing for nitrogen bubbles as underlying embolic material in prosthetic valve carriers.

Adolescent↗
PubMed1996

Microstates in language-related brain potential maps show noun-verb differences.

Brain processing of grammatical word class was studied analyzing event-related potential (ERP) brain fields. Normal subjects observed a randomized sequence of single German nouns and verbs on a computer screen, while 20-channel ERP field map series were recorded separately for both word classes. Spatial microstate analysis was applied, based on the observation that series of ERP maps consist of epochs of quasi-stable map landscapes and based on the rationale that different map landscapes must have been generated by different neural generators and thus suggest different brain functions. Space-oriented segmentation of the mean map series identified nine successive, different functional microstates, i.e., steps of brain information processing characterized by quasi-stable map landscapes. In the microstate from 116 to 172 msec, noun-related maps differed significantly from verb-related maps along the left-right axis. The results indicate that different neural populations represent different grammatical word classes in language processing, in agreement with clinical observations. This word class differentiation as revealed by the spatial-temporal organization of neural activity occurred at a time after word input compatible with speed of reading.

Adult↗
PubMed1996

Event-related potential P300 microstate topography during visual one- and two-dimensional tasks in chronic schizophrenics.

Reports on left-lateralized abnormalities of component P300 of event-related brain potentials (ERP) in schizophrenics typically did not vary task difficulties. We collected 16-channel ERP in 13 chronic, medicated schizophrenics (25 +/- 4.9 years) and 13 matched controls in a visual P300 paradigm with targets defined by one or two stimulus dimensions (C1: color; C2: color and tilt); subjects key-pressed to targets. The mean target-ERP map landscapes were assessed numerically by the locations of the positive and negative map-area centroids. The centroids time-space trajectories were searched for the P300 microstate landscape defined by the positive centroid posterior of the negative centroid. At P300 microstate centre latencies in C1, patients' maps tended to a right shift of the positive centroid (p < 0.10); in C2 the anterior centroid was more posterior (p < 0.07) and the posterior (positive) centroid more anterior (p < 0.03), but without left-right difference. Duration of P300 microstate in C2 was shorter in patients (232 vs 347 ms; p < 0.03) and the latency of maximal strength of P300 microstate increased significantly in patients (C1: 459 vs 376 ms; C2: 585 vs 525 ms). In summary only the one-dimensional task C1 supported left-sided abnormalities; the two-dimensional task C2 produced abnormal P300 microstate map landscapes in schizophrenics, but no abnormal lateralization. Thus, information processing involved clearly aberrant neural populations in schizophrenics, different when processing one and two stimulus dimensions. The lack of lateralization in the two-dimensional task supported the view that left-temporal abnormality in schizophrenics is only one of several task-dependent aberrations.

Adolescent↗
PubMed1996

Instantaneous frequency maps, dipole models and potential distributions of pattern reversal-evoked potential fields for correct recognition of stimulated hemiretinae.

Lateral hemifield pattern-reversal visual evoked potential (PVEP) field data were evaluated using potential distributions, dipole modelling and distributions of Hilbert transformation-based instantaneous frequency in order to determine the stimulated hemisphere. Twenty channel records were collected from 35 normal volunteers in two laboratories using similar stimulus conditions (11-20.5 degrees target, 60-75 min checks, 2/s reversal, 500 ms analysis epoch). P100 latency was determined in each average by the global field power maximum between 90 and 120 ms. Using the data from O1 and O2 at P100 latency, the stimulated hemisphere was identified by maximal potential or minimal instantaneous frequency on the stimulus-contralateral side, or, using the 20-electrodes data at P100 by the ipsilateral lateralization of the dipole model. Correct classification of the stimulated 70 hemiretinae was achieved by potential distribution in 44 cases, by dipole modelling in 54 cases and by instantaneous frequencies in 68 cases. Errors in the classification by potential distribution and dipole location were twice as frequent for decisions based on expected locations over the left than over the right hemisphere. This finding might be caused by the relatively larger size of the left occipital lobe. We conclude that a single value of instantaneous frequency which implies a massive data reduction can serve as a robust parameter for the characterization of the input conditions of hemifield PVEP (i.e. the stimulated hemiretina). It is more successful than potential distribution or dipole modelling, probably because instantaneous frequency incorporates considerably more information than the other two measures. It is suggested to explore instantaneous frequency as a parameter to recognize small retinal area stimuli in perimetry studies.

Adult↗
PubMed1996

Immunomodulation with linomide: possible novel therapy for multiple sclerosis.

Linomide, a synthetic quinoline carboxamide, has the ability to stimulate various lymphocyte subpopulations. We have shown its inhibitory effect on the clinical and histological signs of acute and chronic relapsing EAE. In these models linomide induces suppression of lymphocyte response to antigens, production of autoantibody, antigen presentation to specific T-cell lines and Mac-I expression, and induces activation of NK and suppressor-inducer cells. We have subsequently shown its inhibitory effect on clinical and MRI signs of patients with secondary progressive multiple sclerosis. Results of a double blind, placebo controlled, short term pilot study with p.o. linomide, showed a significant effect on the clinical disability scale (EDSS) (P = 0.045) and on the mean total number of new lesions in serial monthly MRI scans (P = 0.021). The increase of CD45Ra, CD8 and CD16 positive cells in linomide treated patients may indicate the importance of suppressor-inducer, suppressor and NK cells for the inhibition of the autoimmune response in the disease.

Adjuvants, Immunologic↗
PubMed1996

Treatment of secondary progressive multiple sclerosis with the immunomodulator linomide: a double-blind, placebo-controlled pilot study with monthly magnetic resonance imaging evaluation.

Linomide (quinoline-3-carboxamide) is a synthetic immunomodulator that increases the natural killer cell activity. We previously demonstrated that linomide effectively inhibited the clinical and histopathologic signs of acute and chronic relapsing experimental autoimmune encephalomyelitis. We report a double-blind, placebo-controlled study to evaluate tolerability and to obtain preliminary indications of the clinical efficacy of linomide on secondary progressive MS. Thirty patients suffering from clinically definite and laboratory-supported secondary progressive MS, with an expanded disability status scale (EDSS) of 3.0 to 7.0, were included in this study. Patients were treated daily with linomide (2.5 mg) or placebo orally and were followed up for side effects and changes in their neurologic status; monthly MRI scans were taken throughout the treatment period. Twenty-four patients completed at least 6 months of treatment. Mild to moderate side effects, including muscle pains, arthralgia, and edema, were present in 11 of the 15 patients receiving placebo and in 13 of the 15 patients treated with linomide. At 24 weeks, the mean shift in EDSS was +0.272 +/- 0.156 in the placebo group versus -0.166 +/- 0.167 in the linomide group (p = 0.0451). The percentage of patients with evidence of "activity" on their MRI (new, enlarging, or new gadolinium diethylenetriaminepentaacetic acid [Gd-DTPA]-enhancing lesions) throughout the treatment period was 75% in the placebo group and 33% in the linomide group (p = 0.0205). The mean total number of new Gd-DTPA-enhancing lesions per MRI scan for the same period was 0.42 +/- 0.143 in the placebo group and 0.19 +/- 0.114 in the linomide group (p = 0.0387). In this study, linomide proved to be safe and well tolerated in patients with secondary progressive MS. In addition, our results indicate that linomide tends to inhibit the progression of the disease, especially preventing the appearance of new active lesions in the MRI scans. Based on these results, two multicenter phase III trials are currently under way in the United States and in Europe and Australia.

Adjuvants, Immunologic↗
PubMed1996

Responses of growing and finishing turkey toms to dietary lysine.

The present study investigates the lysine requirements of British United Turkey (BUT) Big 6 turkey toms from 8 to 12 and from 16 to 20 wk of age. Growth, feed conversion, and carcass quality responses to increasing dietary lysine levels were measured. From 8 to 12 wk of age (4.0 to 8.8 kg live weight), about 1.20% (4.0 g/Mcal ME) lysine in the diet was found to be adequate to obtain optimum growth and feed conversion, Nitrogen retention also tended to increase with elevated dietary lysine levels in growing turkey toms. From 16 to 20 wk of age (13.1 to 18.5 kg live weight), the highest lysine level of 0.96% (3.0 g/Mcal ME) appeared to be insufficient to maximize weight gain. It is concluded, therefore, that the dietary lysine requirement of finishing turkey toms is 0.96% lysine or higher. In addition to the growth response, a marked increase in breast meat deposition in response to dietary lysine could be observed in finishing turkeys. Increasing dietary lysine decreased intramuscular fat content and grill loss and increased the protein level in breast meat.

Age Factors↗
PubMed1996

Effect of birthweight on pneumonia-specific and total mortality among infants in the highlands of Papua New Guinea.

A cohort of 1711 children born in Tari, Southern Highlands Province, Papua New Guinea was followed to determine the effect of birthweight on total and cause-specific mortality at varying ages during infancy. Mean birthweight was 3.04 kg, males were significantly heavier than females and first offspring significantly lighter than other offspring. Children weighing < or = 2.5 kg at birth accounted for 15% of all births and 32% of all deaths and were 2.7 times more likely to die in infancy than heavier children. Infant mortality was negatively associated with birthweight (p < 0.001). Mortality was very high among children with birthweight < or = 2 kg and was lowest in the 3.1-3.5 kg birthweight category. Pneumonia mortality declined with increasing birthweight in the 1-5 month age group, but in the 6-11 month age group the risk of death from pneumonia was the same among children with birthweight > 3.5 kg as those with birthweight < or = 2.5 kg. While control of infectious diseases will have a marked impact on infant mortality in the short term, longer-term interventions aimed at improving socioeconomic status are needed to improve nutritional status of both adults and children (including birthweight) and hence sustain the lower mortality levels achieved in young children.

Cause of Death↗
PubMed1995

Mapping event-related brain potential microstates to sentence endings.

We analyzed topography and strength of 20 channel event-related potential maps to sentence endings differing in correctness, verbal vs. nonverbal surface form, priming, and repetition count. Seventeen healthy subjects silently read correct and incorrect versions of simple sentences with predictable color endings, and of more complex sentences with predictable composite word endings. Color endings appeared in verbal and nonverbal form. Measures of map topography (centroids of the positive and negative areas of the average referenced maps) and strength (Global Field Power) were analyzed. Adaptive segmentation distinguished a pre-N400 and a N400 microstate in the N400 time range. Topography differed between these two microstates, between verbal and nonverbal endings, and between correct color, incorrect color, and incorrect noncolor words. All verbal endings evoked left-laterlized negativity and right lateralized positivity in the pre-N400 microstates. Correct verbal endings evoked consistent posterior postivity and anterior negativity with left-lateralized gradient strength suggesting language-specific processing. New, incorrect noncolor words evoked reversed anterior-posterior N400 and pre-N400 map topographies with more anterior positivity and more posterior negativity than correct colors in each subject. Gradient strength and current source density maps also differed from those to correct colors. Strongest gradients were left-posterior in the pre-N400 but anterior in the N400 microstate, consistent with anterior activity contributing to the posterior N400 negativity. Incorrect and correct colors, which were semantically primed and repeated, showed smaller topographic differences and N400 effects with a different topography. These different maps can not arise by modulation of a single pattern of neural activity and show that the N400 time range consists of multiple distinct microstates.

Adult↗
PubMed1995

EEG reactivity and EEG activity in never-treated acute schizophrenics, measured with spectral parameters and dimensional complexity.

Our approaches to the use of EEG studies for the understanding of the pathogenesis of schizophrenic symptoms are presented. The basic assumptions of a heuristic and multifactorial model of the psychobiological brain mechanisms underlying the organization of normal behavior is described and used in order to formulate and test hypotheses about the pathogenesis of schizophrenic behavior using EEG measures. Results from our studies on EEG activity and EEG reactivity (= EEG components of a memory-driven, adaptive, non-unitary orienting response) as analyzed with spectral parameters and "chaotic" dimensionality (correlation dimension) are summarized. Both analysis procedures showed a deviant brain functional organization in never-treated first-episode schizophrenia which, within the framework of the model, suggests as common denominator for the pathogenesis of the symptoms a deviation of working memory, the nature of which is functional and not structural.

Acute Disease↗
PubMed1995

Frequency domain source localization shows state-dependent diazepam effects in 47-channel EEG.

The topic of this study was to evaluate state-dependent effects of diazepam on the frequency characteristics of 47-channel spontaneous EEG maps. A novel method, the FFT-Dipole-Approximation (Lehmann and Michel, 1990), was used to study effects on the strength and the topography of the maps in the different frequency bands. Map topography was characterized by the 3-dimensional location of the equivalent dipole source and map strength was defined as the spatial standard deviation (the Global Field Power) of the maps of each frequency point. The Global Field Power can be considered as a measure of the amount of energy produced by the system, while the source location gives an estimate of the center of gravity of all sources in the brain that were active at a certain frequency. State-dependency was studied by evaluating the drug effects before and after a continuous performance task of 25 min duration. Clear interactions between drug (diazepam vs. placebo) and time after drug intake (before and after the task) were found, especially in the inferior-superior location of the dipole sources. It supports the hypothesis that diazepam, like other drugs, has different effects on brain functions depending on the momentary functional state of the brain. In addition to the drug effects, clearly different source locations and Global Field Power were found for the different frequency bands, replicating earlier reports (Michel et al., 1992).

Acoustic Stimulation↗
PubMed1995

Larger topographical variance and decreased duration of brain electric microstates in depression.

The topographical configuration of the spontaneous brain electric fields is considered to contain relevant information about the pattern of the generating cortical electrochemical activation and the associated cognitive processes. Space oriented segmentation allows to break down the stream of the spontaneous EEG into brain electric microstates with stable configuration of the fields. It has been shown that the mean duration of the microstates was consistent with the duration of elementary steps of cognitive processes, and that different topographies of the microstates are associated with different cognitive modalities. Space-oriented segmentation was applied to the resting EEG of 22 depressive patients and of 22 controls. The topographical variance was larger, and the most prominent brain electrical microstates of the EEG epochs were significantly shorter in the depressive group than in controls. No differences were found for the shortest microstates. This result cannot be explained by group differences in the frequency domain of the EEG. No topographical differences were found between the microstates of depressives and those of controls. Based on previous results in healthy volunteers during spontaneous cognition and in schizophrenic patients, the findings indicate that formal aspects rather than the modalities of the stream of cognition are altered in depression. Automatic and schematic processing, and attentional deficits as described in depressive patients might account for the finding of less sustained brain electrical microstates.

Adult↗
PubMed1995

Spontaneous conscious covert cognition states and brain electric spectral states in canonical correlations.

Correlations between subjective, conscious, spontaneous cognitions and EEG power spectral profiles were investigated in 20 normal volunteers (2 sessions each) during relaxation-drowsiness-sleep onset. Four-channel EEG (temporal-parietal and parietal-central, left and right) was continuously recorded. The subjects were prompted 15 times per session to give brief reports of their ongoing thoughts. The reports were rated on 23 scales, and the 16 seconds of EEG recording preceding the prompts were spectral analyzed. Canonical correlation analysis was applied to the data (23 cognition ratings and 124 EEG spectral values for each of the 538 prompts). Four of the 23 pairs of canonical EEG variables and cognition variables were significant (p < 0.016) with correlation coefficients ranging from 0.78 to 0.62. The four pairs of canonical variables showed distinctive features in EEG spectra and cognition styles. The results demonstrate ruleful correspondences between EEG states and spontaneous, conscious, covert, cognitive-emotional states in a no-input, no-task, no-response paradigm.

Adult↗
PubMed1995

Microstate segmentation of spontaneous multichannel EEG map series under diazepam and sulpiride.

Spontaneous multichannel brain electric field (EEG) map series of 20 seconds duration at 1, 15, 30, 45, and 60 minutes after the injection of a single dose of diazepam (13 ss) or sulpiride (6 ss) were segmented into microstates of quasi-constant landscape but varying durations. Post-minus-preinjection difference values were computed for the six microstate variables: specific window size, duration, orientation, distance between windows, and location of center of gravity on the anterior-posterior and left-right axis. Differences between drugs were explored with ANOVAs. Microstate duration increased after sulpiride, and the location of the microstate center of gravity on the anterior-posterior axis moved to a more anterior position after diazepam. The results are in agreement with expectations based on measurements of patients' EEG microstates and with results using estimates of EEG model source locations in the frequency domain. Microstate segmentation appears to be a useful method for physiologically meaningful reduction of multichannel brain electric field data in psychopharmacology.

Adult↗
PubMed1995

Segmentation of brain electrical activity into microstates: model estimation and validation.

A brain microstate is defined as a functional/physiological state of the brain during which specific neural computations are performed. It is characterized uniquely by a fixed spatial distribution of active neuronal generators with time varying intensity. Brain electrical activity is modeled as being composed of a time sequence of nonoverlapping microstates with variable duration. A precise mathematical formulation of the model for evoked potential recordings is presented, where the microstates are represented as normalized vectors constituted by scalp electric potentials due to the underlying generators. An algorithm is developed for estimating the microstates, based on a modified version of the classical k-means clustering method, in which cluster orientations are estimated. Consequently, each instantaneous multichannel evoked potential measurement is classified as belonging to some microstate, thus producing a natural segmentation of brain activity. Use is made of statistical image segmentation techniques for obtaining smooth continuous segments. Time varying intensities are estimated by projecting the measurements onto their corresponding microstates. A goodness of fit statistic for the model is presented. Finally, a method is introduced for estimating the number of microstates, based on nonparametric data-driven statistical resampling techniques.

Algorithms↗
PubMed1995

Immunomodulation of autoimmunity in MRL/lpr mice with syngeneic bone marrow transplantation (SBMT).

MRL-lpr/lpr mice spontaneously develop a severe autoimmune syndrome, characterized by massive generalized lymphadenopathy, arthritis, arteritis, dermatitis and immune complex-mediated glomerulonephritis. Bone marrow transplantation (BMT) from MHC-matched systemic lupus erythematosus (SLE)-resistant donors to susceptible recipients has proved effective in correcting autoimmune manifestations in autoimmune-prone mice. We investigated the effect of syngeneic BMT from MRL/lpr (donor) to immunocompromised MRL/lpr (recipient), after purging the bone marrow inoculum with MoAbs against mature T cells (anti-Thy 1.2). All the untreated mice developed lymphadenopathy and by the age of 36 weeks five of the eight were dead; in contrast, all the mice which underwent syngeneic BMT following acute immunosuppression with total body irradiation (900 cGy) (TBI) remained disease-free. In an additional experiment, it was found that conditioning with cyclophosphamide (CY) before BMT was more effective than TBI in inhibiting delayed-onset autoimmune manifestations (mean survival 350 days in the CY group and 305 days in the TBI group, versus 197 days in untreated controls). Under both immunosuppressive regimens T cell-depleted bone marrow grafts produced far better results than did unmanipulated BMT. Following syngeneic BMT the incidence of proteinuria and the level of serum anti-DNA (dd) antibodies were significantly reduced, compared with that of the age-matched untreated controls. CY was more effective than TBI in reducing the anti-DNA titres. Likewise, T depletion of bone marrow inocula before BMT induced a more drastic drop in autoantibodies, following both CY and TBI conditioning protocols. After syngeneic BMT (either CY or TBI) no signs of lymphadenopathy were observed even at an advanced age. Upon histopathological examination, the BMT-treated mice displayed normal glomeruli with occasional minimal signs of glomerulonephritis. Syngeneic T cell-depleted BMT following acute cytoreduction of anti-self immune lymphocytes may represent a new therapeutic approach for drug-resistant autoimmune diseases.

Animals↗