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Biomedical subjects

J Schwaiger

Publications and source records attributed to J Schwaiger.

13 recordsLinked to original sources
PubMed2001

Alpha and beta band power changes in normal and dyslexic children.

OBJECTIVE: Previous research with healthy subjects suggests that the lower alpha band reflects attentional whereas the upper alpha band semantic processes. The aim of the present study was to investigate whether dyslexics show deficits in attentional control and/or semantic encoding. METHOD: The EEG was recorded while subjects were reading numbers, words and pseudowords and analyzed in a lower and upper alpha and two beta bands (spanning a range of about 8--16 Hz). A phasic response is measured in terms of a decrease in event related band power during reading with respect to a reference interval. Tonic power is measured in terms of (log) band power during a reference interval. RESULTS: In the lower alpha band dyslexics show an increased phasic response to words and pseudowords at right hemispheric sites but a lack to respond to words at O1. The upper alpha band exhibits a highly selective phasic response to words at left frontal sites but for controls only, whereas dyslexics show a general increase in tonic upper alpha power. Whereas the low frequency beta band (beta-1a) exhibits a rather diffuse pattern, a highly selective finding was obtained for the beta-1b band. CONCLUSIONS: Dyslexics have a lack of attentional control during the encoding of words at left occipital sites and a lack of a selective topographic activation pattern during the semantic encoding of words. Because only in controls reading of words is associated with a strong beta-1b desynchronization at those recording sites which correspond to Broca's area (FC5) and the angular gyrus (CP5, P3), we may conclude that this frequency band reflects the graphemicphonetic encoding of words.

Alpha Rhythm↗
PubMed2001

Theta band power changes in normal and dyslexic children.

OBJECTIVE: Tonic and phasic (event-related) theta band power changes were analyzed in a sample of 8 dyslexic and 8 control children. Previous research with healthy subjects suggests that electroencephalograph (EEG) theta activity reflects the encoding of new information into working memory. The aim of the present study was to investigate whether the processing deficits of dyslexics are related to a reduced phasic theta response during reading. METHOD: The EEG was recorded while subjects were reading numbers, words and pseudowords and analyzed in a lower and upper theta band (4--8 Hz). A phasic response is measured in terms of an increase in event related band power during reading with respect to a reference interval. Tonic power is measured in terms of (log) band power during a reference interval. RESULTS: Large group differences in tonic and phasic lower theta were found for occipital sites where dyslexics show a complete lack of pseudoword processing. For words, only controls show a highly selective left hemispheric processing advantage. CONCLUSIONS: Dyslexics have a lack to encode pseudowords in visual working memory with a concomitant lack of frontal processing selectivity. The upper theta band shows a different pattern of results which can be best interpreted to reflect the effort during the encoding process.

Child↗
PubMed2000

The time locked theta response reflects interindividual differences in human memory performance.

Recent research indicates that an increase in theta band power is related to episodic memory performance. In this study with human subjects, the evoked (time locked) and induced (not time locked) theta response is analyzed in a recognition task. The results show a strong evoked theta response during an early retrieval period of up to 400 ms. Only for good memory performers theta is strictly time locked, indicating that theta peaks appear in preferred time windows after a target is presented. This effect--which coincides with a large P3--suggests that good performance requires a strict timing of different processing stages that correspond to cycles of theta activity.

Adult↗
PubMed2000

Chronic toxicity of nonylphenol and ethinylestradiol: haematological and histopathological effects in juvenile Common carp (Cyprinus carpio).

In recent ecotoxicological research, there is an increasing concern about alkylphenolic industrial chemicals, such as nonylphenol (NP), because of their estrogenic properties. Data on the general fish toxicity of these wide spread aquatic pollutants are scarce. In order to evaluate sublethal toxic effects of environmentally relevant concentrations of NP, juvenile Common carp (Cyprinus carpio) were exposed to NP concentrations ranging from 1 to 15 microg NP/l over a 70-day period. Classical toxicological endpoints, such as various haematological parameters and histopathological alterations were investigated. In a comprehensive protocol, besides NP-induced effects also alterations due to a treatment with the synthetic estrogen ethinylestradiol (EE2) were evaluated. After both the NP-exposure as well as the EE2-treatment, the predominant haematological finding was a severe anaemia. Histopathological alterations in the kidney, the liver and the spleen occurred exclusively after treatment with EE2, whereas NP-exposed fish did not show any tissue lesions. Depending on the haematological parameter examined, a NOEC between 1 and 5 microg NP/l could be established. From the present findings, it is assumed, that under field conditions, the NP-induced, general toxic effects, might outbalance the relatively weak estrogenic effects of this compound and possibly might disturb ecologically relevant processes such as fish reproduction.

Animals↗
PubMed2000

Theta oscillations and the ERP old/new effect: independent phenomena?

OBJECTIVES: The hypothesis is examined whether a memory-related change in induced band power (oscillatory old/new effect) is functionally related to a memory-related increase in ERP positivity (ERP old/new effect). METHODS: In order to avoid a confounding on the measurement level, induced band power (IBP) was used as a measure that is devoid of the influence of evoked components. The EEG was recorded during a recognition memory task. RESULTS: The results show that compared to correctly rejected words, targets (remembered words) elicit a significantly larger P300. An oscillatory old/new effect was found for the delta and theta but not for the alpha band. It is manifested by an increase in delta and theta IBP which is significantly larger for targets than for correctly rejected words. It can be observed during the same time interval and shows the same topographic distribution as the ERP old/new effect. Most importantly, however, the ERP old/new effect (as well as the P300 itself) is generated by very slow frequencies which lie below the delta band. CONCLUSIONS: These findings demonstrate that the two types of old/new effects are functionally related. Possible physiological mechanisms underlying this relationship are discussed in terms of a threshold change in the cortex (generating the P300) that occurs during an increase in hippocampal theta activity (generating an increase in induced theta power).

Adult↗
PubMed1999

'Paradoxical' alpha synchronization in a memory task.

The results of a specially designed memory search paradigm which maximizes episodic short-term memory (STM) and minimizes semantic long-term memory (LTM) demands show that the upper alpha band synchronizes selectively in those conditions and time intervals where episodic STM demands are maximal. This finding of a selective alpha synchronization occurring only in the upper alpha band and during highest task demands is surprising because it is well known that usually alpha desynchronizes during mental activity. Because experiments from our laboratory indicate that desynchronization in the upper alpha band is related to semantic LTM processes, the present finding suggests that a selective synchronization in this frequency band reflects inhibition of semantic LTM. It is assumed that once the capacity limits of STM are reached or exceeded, processing resources are no longer distributed and that potentially interfering, task irrelevant, brain areas or processing systems are inhibited.

Adult↗
PubMed1998

Theta synchronization in the human EEG and episodic retrieval.

Event-related desynchronization (ERD) and synchronization (ERS) was measured during episodic retrieval in a specially designed recognition task which forces subjects to avoid semantic search strategies. ERD represents the percentage of a decrease, ERS an increase in band power. The results show that only the theta band differentiates between good and bad episodic memory performers and that good performance is related to a large degree of theta synchronization. The delta and alpha bands did not yield significant effects. Topographical differences in theta ERS reveal that good performers use primarily their right hemisphere to retrieve episodic information. This finding agrees with respective results from PET studies.

Adult↗
PubMed1998

Induced alpha band power changes in the human EEG and attention.

Induced alpha power (in a lower, intermediate and upper band) which is deprived from evoked electroencephalograph (EEG) activity was analyzed in an oddball task in which a warning signal (WS) preceded a target or non-target. The lower band, reflecting phasic alertness, desynchronizes only in response to the WS and target. The intermediate band, reflecting expectancy, desynchronizes about 1 s before a target or non-target appears. Upper alpha desynchronizes only after a target is presented and, thus, reflects the performance of the task which was to count the targets. Thus, only slower alpha frequencies reflect attentional demands such as alertness and expectancy.

Adult↗
PubMed1996

Event-related desynchronization (ERD) and the Dm effect: does alpha desynchronization during encoding predict later recall performance?

Based on previous research which has shown that event-related desynchronization (ERD) in the lower and upper alpha band reflects attentional and semantic processing respectively, the present study examines the hypothesis whether event-related shifts in the two alpha bands are capable of predicting later recall performance. In an incidental memory paradigm, subjects first had to judge the category membership for a set of 96 words. Later, without prior warning, subjects were asked to recall the words. The results show that for good performers, the extent of ERD in the lower alpha band during the semantic encoding for words is significantly larger for remembered as compared to not remembered words, whereas for bad performers the ERD in the upper alpha band is significantly more pronounced. This type of Dm effect is particularly strong over parietal recording sites in both hemispheres. In referring to the proposed interpretation of the lower and upper alpha band, the present findings seem to indicate that in contrast to good performers, bad performers are less attentive or alert during encoding. Event-related potentials (ERPs) also yielded significant Dm effects at parietal recording sites.

Adult↗
PubMed1994

Episodic and semantic memory: an analysis in the EEG theta and alpha band.

This study examines the hypothesis that in contrast to semantic memory processes that are assumed to be reflected primarily within the alpha band, episodic memory processes are related to activity within the theta band. EEG signals were recorded from subjects as they performed a semantic congruency and an episodic recognition task. In the semantic task, subjects had to judge whether or not sequentially presented concept-feature pairs (such as "eagle-claws" or "pea-huge") are semantically congruent. In the episodic task, which followed the semantic task without prior warning, the same word pairs were presented together with new distractors (generated by repairing known concept-feature pairs). Here, subjects judged whether or not a particular concept-feature pair was already presented during the semantic task. EEG data were analyzed using event-related desynchronization (ERD) as a measure for the amount of event-related changes in band power in the theta band and in the upper and lower alpha bands. The alpha band was determined individually, using the alpha peak frequency during the resting period as the cut-off point to separate the lower from the upper alpha band. The results, which are based on those identical word pairs that demanded a yes response in both tasks, showed that semantic memory processes are indeed primarily reflected in the upper alpha band whereas episodic memory processes are reflected in the theta band. The possible relationship between hippocampal theta activity and the encoding of episodic information is discussed.

Adult↗
PubMed1992

Early diagnosis of ovarian torsion by color Doppler ultrasonography.

Ovarian torsion is often difficult to diagnose because of the nonspecific nature of the clinical findings. We report on the use of color Doppler ultrasonography in diagnosing early ovarian torsion. This technique provides a highly specific finding, the absence of blood flow to the ovary, that greatly facilitates the diagnosis of ovarian torsion.

Adult↗
PubMed1992

A framework for the knowledge-based interpretation of laboratory data in intensive care units using deductive database technology.

In co-operation with the Institute of Anaesthesiology of the Ludwig-Maximilians-University in Munich a computer-based system for the analysis and interpretation of renal function, fluid and electrolyte metabolism of critical care patients has been developed. This paper focuses on the requirements and implementation aspects of the knowledge-based interpretation for this particular system. Objective of the proposed approach is, to transform an enormous--and constantly increasing--amount of raw data available in modern intensive care units (ICUs) into relevant, patient-oriented information, which is easy to understand by the medical staff. The essential features of a knowledge-based system at an ICU are outlined. A system is described where these features are realized using deductive database technology as a specification paradigm and extended relational databases as an implementation platform. The integration into the hospital information system is highlighted.

Artificial Intelligence↗