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Biomedical subjects

S Lis

Publications and source records attributed to S Lis.

At least 19 recordsLinked to original sources
PubMed2006

Luminescence characterisation of the reaction system histidine-KBrO3-Tb(III)-H2SO4.

Chemiluminescence of the system containing Tb(III) ions, histidine and bromate ions in acid solution was studied. The kinetic curves and CL emission spectra of the system were discussed. The emission spectrum of the histidine-Tb(III)-KBrO3-H2SO4 system revealed two emission maxima at approximately 490 and 550 nm, characteristic of Tb(III) ions. Values of lifetimes of the Eu(III) excited states in Eu(III)-histidine system have shown that the histidine formed ML and ML2 complexes in neutral solution and did not make them in acidic environment. On the basis of the results, a possible mechanism of reaction system: histidine-Tb(III)-KBrO3-H2SO4 is presented.

Bromates↗
PubMed2005

Application of cause-and-effect analysis to potentiometric titration.

A first attempt has been made to interpret physicochemical data from potentiometric titration analysis in accordance with the complete measurement-uncertainty budget approach (bottom-up) of ISO and Eurachem. A cause-and-effect diagram is established and discussed. Titration data for arsenazo III are used as a basis for this discussion. The commercial software Superquad is used and applied within a computer-intensive resampling framework. The cause-and-effect diagram is applied to evaluation of seven protonation constants of arsenazo III in the pH range 2-10.7. The data interpretation is based on empirical probability distributions and their analysis by second-order correct confidence estimates. The evaluated data are applied in the calculation of a speciation diagram including uncertainty estimates using the probabilistic speciation software Ljungskile.

Arsenazo III↗
PubMed2001

Application of cause-and-effect diagrams to the interpretation of UV-Vis spectroscopic data.

The application of cause-and-effect diagrams to the evaluation of thermodynamic data from UV-Vis absorption spectroscopic analysis is demonstrated. The contributions of measurement uncertainty identified from a cause-and-effect diagram are implemented into a Monte Carlo procedure based on the threshold bootstrap computer-assisted target factor analysis (TB CAT). This algorithm aims at an improvement of data comparability and accounts for non-normality, spectral, residual and parameter correlation as well as random noise in target factor analysis. The ISO Type-B measurement uncertainties are included into the process by normally distributed random numbers with specified mean values and dispersions. The TB CAT procedure is illustrated by a flow diagram and a case study of Nd(III) complexation by picolinic acid N-oxide (pic NO) in aqueous solution. Using 12 experimental spectra as input data, the single component spectra and the formation constant 1g betaML of the Nd(pic NO)2+ species are obtained together with the respective probability density distributions. The role of the cause-and-effects approach on the further development of chemical thermodynamics is discussed.

Journal Article↗
PubMed2001

Quantitative resolution of spectroscopic systems using computer-assisted target factor analysis (CAT).

Factor analysis (FA) is widely applicable in analytical chemistry. For suitable data structures, the generality of the approach is a strong point of FA. Using target testing procedures, a wealth of specific informations on the components in a chemical system can be extracted without stating a specific model. Target testing, however, is time-consuming and often heuristic. In the following, application of a computer-assisted target factor analysis (CAT) algorithm is described. CAT estimates a rotation matrix that transforms abstract factors into physically meaningful informations by using general constraints, i.e. non-negativity of absorptions and/or concentrations. Thus, the rotation step in factor analysis is automated and allows application of target factor analysis to situations where none or only very limited information on the real factors and their respective contributions is available. Thus, a target testing procedure of guessing physically meaningful factors and iteratively adapting these factors is performed automatically. Nevertheless, CAT is not a black box procedure. The relative importance of different optimization constraints is balanced interactively. CAT can be applied to all situations where factor analysis can be used. CAT is demonstrated using UV-Vis absorption spectra of a Nd(III) polyoxometalate cryptate system and the system U(VI)-CO2-H2O as examples.

Journal Article↗
PubMed2001

Cognitive subprocesses and schizophrenia. A. Reaction-time decomposition.

OBJECTIVE: The aim of the study is to demonstrate that deficits of information processing in schizophrenic patients can be isolated with reaction-time (RT) decomposition paradigms. METHOD: Three types of visually presented tasks were applied: simple, disjunctive and choice RT-tasks. RT were split into movement latency and time necessary to execute movements. Comparisons of three samples of schizophrenic patients (295.3) with individually matched (age, sex. education and handedness) healthy controls are presented: Sample 1: 10 drug-naive first-onset patients, Sample 2: 10 neuroleptically treated first-onset patients, Sample 3: 10 neuroleptically treated chronically ill patients. RESULTS: Findings indicate that schizophrenia affects primarily subprocesses in which percepts are translated into appropriate actions (response-selection). Neuroleptic treatment improves processing at this stage but is accompanied by slowing of movement execution. CONCLUSION: Response-selection is selectively impaired in first-onset patients. This disturbance, which might be specific for schizophrenia, can be regarded as indication of a disconnection between frontal and posterior areas.

Adult↗
PubMed2001

Cognitive subprocesses and schizophrenia. B. Maze tasks.

OBJECTIVE: In a companion paper we demonstrated that in reaction-time tasks the response selection stage is selectively disturbed in schizophrenia. The aim of the present study is the investigation of subprocesses, which are incorporated into repeatedly activated loops of cognitive processes and need additional information from working memory. METHOD: Maze tasks of varying complexity (with and without bifurcations) were presented to drug-naive and treated first-onset schizophrenic patients. The tasks had to be solved under easy and difficult motor-conditions. Both patient samples were compared with healthy control groups matched by age, sex, education and experience with the experimental setting. RESULTS: In mazes with alternative routes patients exhibited the expected decrease of performance. However, untreated patients improved under difficult motor conditions. This improvement is smaller after neuroleptic treatment. CONCLUSION: Under difficult motor conditions attention is focused on the execution of movements and thus withdrawn from perceiving irrelevant response alternatives, i.e. the effects of disturbed response selection are reduced.

Adult↗
PubMed2001

Reaction-times and bioelectrical brain signals of drug-naive schizophrenic first-onset patients in identification and classification tasks.

OBJECTIVE: The question of the present study is whether disturbances of response-selection in schizophrenic patients are discernible only if overt motor-actions are required, or also if covert cognitive actions are necessary. METHOD: Visual identification (digits) and classification (dot-enumeration) tasks were presented to 18 drug-naive, first-onset schizophrenic patients and healthy controls. It is assumed that enumeration of more than three dots requires additional cognitive processes as buffering and re-focusing of attention. Reaction-times and 21-channel-EEG were measured. For eye-movement artefact-elimination a new non-parametric regression approach was applied. RESULTS: Reaction-times revealed that in the patient group response selection is lengthened in both tasks. Perception of dot numbers is not affected. Bioelectrical data depicted a left-lateralization of posterior P100 and N 100 in the patient group as well as an enhanced fronto-central P200. CONCLUSION: Whereas in reaction-times of patients only a disturbance of response selection is discernible, bioelectrical measurements also point to an altered organization of perceptive processes.

Adult↗
PubMed1999

Cognitive dysfunction in schizophrenia: a new set of tools for the assessment of cognition and drug effects.

Cognitive impairment in schizophrenia must be seen as a disturbance of cortico-sub-cortical connectivity with a neurotransmitter imbalance in a circuitry system, which connects thalamic input with prefrontal processing and supplementary motor cortex and basal ganglia output. The concept of maze-solving behaviour as a continuous cognitive task evoking a conflict between prefrontal cortex and basal ganglia activity is explained and introduced to distinguish between the effects of D2 blocking agents and substances with a predominant 5HT2A receptor affinity, such as clozapine and risperidone. Complex mazes show a cognitive deficit in untreated schizophrenic patients that are impaired by conventional and improved by atypical antipsychotic substances. Processing speed improves most on clozapine, while parallel processing is best supported by the non-sedative atypical substance risperidone. Maze paradigms are presented.

Antipsychotic Agents↗
PubMed1998

The topography of non-linear cortical dynamics at rest, in mental calculation and moving shape perception.

Differential cortical activation by cognitive processing was studied using dimensional complexity, a measure derived from nonlinear dynamics that indicates the degrees of freedom (complexity) of a dynamic system. We examined the EEG of 32 healthy subjects at rest, during a visually presented calculation task, and during a moving shape perception task. As a nonlinear measure of connectivity, the mutual dimension of selected electrode pairs was used. The first Lyapunov coefficient was also calculated. Data were tested for non-linearity using a surrogate data method and compared to spectral EEG measures (power, coherence). Surrogate data testing confirmed the presence of nonlinear structure in the data. Cognitive activation led to a highly significant rise in dimensional complexity. While both tasks activated central, parietal and temporal areas, mental arithmetic showed frontal activation and an activity maximum at T3, while the moving shape task led to occipital activation and a right parietal activity maximum. Analysis of mutual dimension showed activation of a bilateral temporal-right frontal network in calculation. The Lyapunov coefficient showed clear topographic variation, but was not significantly changed by mental tasks (p<.09). While dimensional complexity was almost unrelated to power values, nonlinear (mutual dimension) and linear (coherence) measures of connectivity shared up to 37% of variance. Data are interpreted in terms of increased cortical complexity as a result of recruitment of asynchronously active, distributed neuronal assemblies in cognition. The topography of nonlinear dynamics are related to neuropsychological and neuroimaging findings on mental calculation and moving shape perception.

Adult↗
PubMed1997

Can negative self-schemes in depressives be altered through sleep deprivation?

This paper addresses the question whether negative cognitive style represents a state or trait variable of depressive patients. For this reason, it studies the influence of sleep deprivation on negative self-schemes of those patients. 10 patients suffering from DSM-III-R major depression were compared with 10 age- and sex-matched controls on a task for rating the self-descriptiveness of positive and negative adjectives as well as a subsequent word recognition task. Three sessions were involved: an initial session (baseline), the second following a night of sleep deprivation, and the third after a successive full night's sleep. During the baseline examination, depressives showed a relatively negative cognitive bias; that is, the same number of positive and negative self-scheme elements. In comparison to controls, they showed significantly more negative and significantly less positive self-scheme elements. The same pattern emerged in a word recognition task for the number of recognized self-scheme elements. These variables indicated no change in the depressive group following sleep deprivation. Depressive subjects' reaction times on self-descriptiveness rating were significantly longer for positive than for negative self-scheme elements at the baseline session. The opposite was true for controls. Here, a sleep deprivation effect was evident. There was no longer a difference in the speed of information processing for positive as compared to negative self-scheme elements. This applied to both depressive and control groups.

Adult↗
PubMed1997

Improvement of cognitive function in schizophrenic patients receiving clozapine or zotepine: results from a double-blind study.

Clinical interest in the so-called atypical antipsychotics currently focuses on the possibility of improving the negative symptoms of schizophrenia and the cognitive dysfunction associated with the disease. While clozapine has been shown to be effective in this respect, no data are available on zotepine. We report on a double-blind randomized study designed to evaluate the impact of zotepine and clozapine on cognitive dysfunction in schizophrenia. Cognitive function was operationalized by a maze test in which patients traversed computer-displayed mazes of increasing complexity. Passage time, route, and motor errors were evaluated. 25 schizophrenic (DSM-IIIR) patients were included in each group. After washout, they were randomized on zotepine or clozapine and given up to 450 mg of substance each. Patients were followed for six weeks and evaluated weekly. We report on a subsample of 26 patients matched for baseline BPRS, SANS, and age. 13 matched healthy persons were recruited as controls. ANOVA with group and course over time as factors was used for analysis. Both clozapine and zotepine achieved a highly significant decrease in overall symptoms (BPRS) and negative symptoms (SANS). Zotepine and clozapine were equally effective. In the maze tests, motor errors in simple mazes were stable over time and differentiated schizophrenics from controls as a "trait" marker. In passage time and maze route, schizophrenics performed worse than controls. An improvement by medication was evident in both medication groups, but was more pronounced in the zotepine-treated group. The study confirms previous results on the efficacy of clozapine and zotepine in treating negative symptoms of schizophrenia. The data presented show for the first time that zotepine is efficacious in improving cognitive dysfunction, confirming this substance's value as an atypical antipsychotic.

Adult↗
PubMed1997

Conventional versus atypical neuroleptics: subjective quality of life in schizophrenic patients.

BACKGROUND: The effectiveness of antipsychotic drugs against positive psychotic symptoms has been demonstrated in many studies, but their effects on quality of life have yet to be clarified. The impact of different neuroleptic therapies on the subjective quality of life of schizophrenic patients is evaluated in a cross-sectional open study. METHOD: During a four-month period a standardised quality of life interview for schizophrenic patients was applied on day 10 after admission; 33 patients on atypical neuroleptics (AAP) were compared with 31 matched patients on conventional neuroleptics (CAP). RESULTS: The AAP group had significantly higher scores in general quality of life as well as in different life domains: physical well-being, social life and everyday life. In separate comparisons of the AAP group, patients on clozapine and risperidone were found to have a higher quality of life score than patients on CAP or zotepine. CONCLUSIONS: The pharmacological profile of clozapine and risperidone may provide a basis for explaining the higher subjective quality of life found in this study. The lower quality of life of the CAP group may possibly be related to intrinsic effects of the conventional antipsychotics.

Adult↗
PubMed1996

Effect of tetrahydroaminoacridine on sleep in healthy subjects.

The present study investigated the impact of the cholinesterase inhibitor tetrahydroaminoacridine (THA; tacrine) on sleep in healthy subjects. According to the reciprocal interaction model of non-rapid eye movement (NREM) and REM sleep regulation, which postulates a primary role in cholinergic neurotransmission for the initiation and maintenance of REM sleep, it was expected that THA would lead to an earlier onset of REM sleep. In 12 healthy subjects aged from 21 to 50 years two different doses (20 mg, 40 mg) were administered 1 hour prior to bed time and compared to placebo. Only the higher dose of THA significantly shortened REM latency. No other significant effects on sleep architecture were observed, although administration of 40 mg tacrine was associated with a decrease in sleep efficiency and a prolongation of sleep latency. Blood plasma levels of tacrine and its metabolite 1-hydroxytacrine measured prior to sleep and during the first 90 min of sleep were significantly correlated with the onset of REM sleep in relation to the timing of drug administration (only for the 20 mg dose). The reversible cholinesterase inhibitor THA exerts effects on REM latency comparable to those observed with other cholinomimetic agents.

Adult↗
PubMed1996

Cognitive dysfunction in schizophrenia: comparison of treatment with atypical antipsychotic agents and conventional neuroleptic drugs.

Impaired cognitive function is both a feature of schizophrenia and a side effect of conventional neuroleptics. Maze tests were used to determine the effects on cognition of conventional dopamine antagonist neuroleptics (haloperidol and fluphenazine) and the newer serotonin-dopamine antagonist antipsychotics (risperidone and clozapine). Patients on clozapine or risperidone showed better performance on the maze tasks than untreated patients or patients taking conventional neuroleptics. In particular, patients treated with risperidone or clozapine were better able to maintain motor coordination while they focused on the more complex "frontal" maze tasks which required sequencing and planning. In view of the restrictions on the use of clozapine, it is suggested that risperidone should be more widely used in schizophrenia because it preserves cognitive function better than conventional neuroleptics and is therefore likely to allow patients to have better insight into their illness and to have better long-term quality of life expectations.

Clozapine↗
PubMed1995

Induction of cytokine synthesis and fever suppresses REM sleep and improves mood in patients with major depression.

Beneficial effects of inflammatory events on certain psychiatric disorders, including depression, were reported sporadically by ancient Greek physicians, but have been described also in our times by a few psychiatrists during the past decades. During febrile inflammatory events, mediators of the immune system such as interleukin-1 can be detected in the brain and may act on their respective receptors which have also been demonstrated in the brain. Since cytokines such as interleukin-1 have been shown in animal studies to exert sedative behavioral effects, to be somnogenic, and to induce slow-wave sleep (SWS), we performed a pilot study to evaluate scientifically the anecdotically reported beneficial effects of inflammatory states on depressive disorders. Mood and sleep parameters were monitored in seven drug-free, severely depressed patients before, during, and after the administration of a single dose of endotoxin. All patients responded with a short pulse of increased synthesis of the cytokines tumor necrosis factor, interleukin-1, and interleukin-6 and elevated body temperature for several hours. During the night following endotoxin administration, rapid eye movement (REM) sleep was significantly suppressed, while changes in slow wave sleep were not significant. During the next day, all patients were in a significantly improved mood; however a rebound of REM sleep was observed in the second night after endotoxin administration and mood worsened again during the next days, indicating an only transient beneficial effect of the treatment.

Adult↗
PubMed1995

Some considerations on estimating event-related brain signals.

Understanding the timing of mental acts is one of the prominent questions in information processing research. The analysis of event related potentials (ERP) with their high temporal resolution might make access to cognition related brain activity possible. We consider three major problems which make the application of ERPs questionable and then propose some solutions to these problems. The primary problem concerns the separation of the ERPs from the background EEG which is not related to the stimulus. The most common method used is averaging. We argue that this is not the most appropriate method and suggest an alternative for estimating the signal in single-trial recordings. Artifacts present a second problem. We will first review established methods of dealing with eye-movement artifacts and then propose an alternative. We will also report on current work on the parametrisation of single-trial signal estimates, which constitute the third problem considered.

Algorithms↗
PubMed1994

Sleep EEG of patients with obsessive-compulsive disorder.

Twenty-two patients suffering from an obsessive and compulsive disorder (OCD) according to DSM-III-R were investigated by polysomnographic sleep EEG recordings under drug-free conditions and compared to age- and sex-matched healthy controls. Sleep efficiency was significantly lower and wake % SPT was significantly increased in the patient group compared to healthy subjects. Sleep architecture did not differ among the two samples. Especially REM sleep measures, in particular, REM latency did not differ among the groups. No positive correlation was found between sleep variables and rating inventories for obsession and compulsions (Y-BOCS), depression (Hamilton) and anxiety (CAS). A secondary depression did not influence sleep EEG variables. The results of this study contradict the assumption that OCD patients show REM sleep and slow wave sleep abnormalities similar to those shown by patients with primary depression.

Adult↗