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Biomedical subjects

P Rappelsberger

Publications and source records attributed to P Rappelsberger.

At least 19 recordsLinked to original sources
PubMed2001

Low-resolution brain electromagnetic tomography revealed simultaneously active frontal and parietal sleep spindle sources in the human cortex.

Analyses of scalp-recorded sleep spindles have demonstrated topographically distinct slow and fast spindle waves. In the present paper, the electrical activity in the brain corresponding to different types of sleep spindles was estimated by means of low-resolution electromagnetic tomography. In its new implementation, this method is based on realistic head geometry and solution space is restricted to the cortical gray matter and hippocampus. In multichannel all-night electroencephalographic recordings, 10-20 artifact-free 1.25-s epochs with frontally, parietally and approximately equally distributed spindles were marked visually in 10 normal healthy subjects aged 20-35years. As a control condition, artifact-free non-spindle epochs 1-3s before or after the corresponding spindle episodes were marked. Low-resolution electromagnetic tomography demonstrated, independent of the scalp distribution, a distributed spindle source in the prefrontal cortex (Brodmann areas 9 and 10), oscillating with a frequency below 13Hz, and in the precuneus (Brodmann area 7), oscillating with a frequency above 13Hz. In extremely rare cases only the prefrontal or the parietal source was active. Brodmann areas 9 and 10 have principal connections to the dorsomedial thalamic nucleus; Brodmann area 7 is connected to the lateroposterior, laterodorsal and rostral intralaminar centrolateral thalamic nuclei. Thus, the localized cortical brain regions are directly connected with adjacent parts of the dorsal thalamus, where sleep spindles are generated. The results demonstrated simultaneously active cortical spindle sources which differed in frequency by approximately 2Hz and were located in brain regions known to be critically involved in the processing of sensory input, which is in line with the assumed functional role of sleep spindles.

Adult↗
PubMed2001

EEG frequency and phase coupling during human information processing.

Neuronal activity during information processing is represented by oscillations within local or widespread neuronal networks. These oscillations may be recorded by the EEG (electroencephalogram). The oscillatory interaction between neuronal ensembles may be at one single frequency or at different frequencies due to non-linear coupling. The investigation of momentary coherence and phase enables the examination of synchronized oscillatory network activity during fast-changing cognitive processes. On this basis information transfer from occipital areas towards frontal areas could be described during processing of visual presented words. Non-linear phase coupling between oscillations with different frequencies during memory processing was detected by means of cross-bicoherence.

Adult↗
PubMed2000

Theta synchronization predicts efficient memory encoding of concrete and abstract nouns.

Functional and topographical differences between processing of spoken nouns which were remembered or which were forgotten were shown by means of EEG coherence analysis. Later recalled nouns were related with increased neuronal synchronization (= cooperation) between anterior and posterior brain regions regardless of presented word category (either concrete or abstract nouns). However, theta coherence exhibited topographical differences during encoding of concrete and abstract nouns whereby former were related with higher short-range (mainly intrahemispheric), later with higher long-range (mainly interhemispheric) coherence. Thus, theta synchronization possibly is a general phenomenon always occurring if task demand increases and more efficient information processing is required. Measurement of EEG coherence yields new information about the neuronal interaction of involved brain regions during memory encoding of different word classes.

Adult↗
PubMed2000

Long-range EEG synchronization during word encoding correlates with successful memory performance.

Distinct cortical activity during memory encoding of words, which were either recalled or not, was reported by a number of studies. This activity was mainly found at frontal and temporal/parietal brain regions. However, it was not clear if these regions interact with each other or work independently. In order to get a functional measure of the degree of neuronal large-scale cooperation, we calculated EEG coherence, which provides a statistical measure of synchronization between two EEG signals per frequency band. Therefore, coherence enables us to assess the functional interaction between cell assemblies of distant brain regions. The purpose of our study was to investigate if successfully recalled words show enhanced cortical synchronization compared with not recalled ones. Additionally, the influence of stimulus modality and the way different EEG frequencies participate in this process was examined. The EEG of 25 participants was recorded during memory encoding of concrete German nouns, either presented auditorily or visually and stimuli were separated according to the participant's memory performance. Recalled nouns exhibited overall enhanced synchronization but showed typical patterns, especially between anterior and posterior brain regions in all frequency bands except the alpha-1 band (8-10 Hz). Recalling nouns was accompanied by increased synchronization between more distant electrodes in relation to an increase of synchronization between adjacent electrodes. Moreover, the degree of intrahemispheric synchronization was higher for recalled nouns. The pattern of EEG coherence and amplitude changes during verbal memory encoding allowed us to assess the probability that nouns would be recalled or not.

Acoustic Stimulation↗
PubMed1999

Adaptive phase estimation and its application in EEG analysis of word processing.

Oscillations are a general phenomenon of neuronal activity during information processing. Mostly, widespread networks are involved in brain functioning. In order to investigate network activity coherence analysis turned out to be a useful tool for examining the functional relationship between different cortical areas. This parameter allows the investigation of synchronisation phenomena with regard to defined frequencies or frequency bands. Coherence and cross phase are closely connected spectral parameters. Coherence may be understood as a measure of phase stability. Whereas coherence describes the amount of information transfer, the corresponding phase, from which time delays can be computed, hints at the direction of information transfer. Mental processes can be very brief and coupling between different areas may be highly dynamic. For this reason a two-dimensional approach of adaptive filtering was developed to estimate coherence and phase continuously in time. Statistical and dynamic properties of instantaneous phase are discussed. In order to demonstrate the value of this method for studying higher cognitive processes the method was applied to EEG recorded during word processing. During visual presentation of abstract nouns an information transfer from visual areas to frontal association areas in the Alpha1 frequency band could be verified within the first 400 ms. The Alpha1 band predominately seems to reflect sensory processing and attentional processes. In addition to conventional coherence analyses during word processing phase estimations may yield valuable new insights into the physiological mechanisms during word processing.

Adult↗
PubMed1999

Gender dependent EEG-changes during a mental rotation task.

This study is based on 30 students, 15 females and 15 males. EEG was recorded with 19 electrodes according to the international 10/20 system against averaged signals picked up from both ear lobes. Averaged power spectra and cross-power spectra between all electrode-positions were computed. Data were reduced to five frequency bands (theta, alpha1, alpha2, beta1 and beta2) and finally mean amplitude and coherence were computed. EEG-recordings were made during a mental rotation task (Shepard-figures). The obtained spectral parameters were compared with the corresponding values of a baseline activity with eyes open at rest. The results of statistical evaluations (paired Wilcoxon tests, Wilcoxon tests of independent samples) were presented in error probability maps. In males, local coherence decreased between the posterior left electrodes in the theta-band. In females, a decrease of coherence between the posterior right electrodes were observed in this frequency-band. In contrast to females, males showed an increase of coherence between frontal, central and parietal electrode positions in both hemispheres in the alpha1-band. The increase of local coherence in the beta1-band over the right temporo-parietal sites in the male group was more pronounced than in the female group. Especially in females, interhemispheric coherence increased between the posterior electrodes in the theta-, beta1- and beta2-ranges. This study suggests the involvement of many brain areas during mental rotation. Females show a rather symmetrical allocation of coherence increase in theta, beta1 and beta2.

Adult↗
PubMed1999

Synchronization between temporal and parietal cortex during multimodal object processing in man.

A series of recordings in cat visual cortex suggest that synchronous activity in neuronal cell ensembles serves to bind the different perceptual qualities belonging to one object. We provide evidence that similar mechanisms seem also to be observable in human subjects for the representation of supramodal entities. Electroencephalogram (EEG) was recorded from 19 scalp electrodes (10/20 system) in 19 human subjects and EEG amplitude and coherence were determined during presentation of objects such as house, tree, ball. Objects were presented in three different ways: in a pictorial presentation, as spoken words and as written words. In order to find correlates of modality-independent processing, we searched for patterns of activation common to all three modalities of presentation. The common pattern turned out to be an increase of coherence between temporal and parietal electrodes in the 13-18 Hz beta1 frequency range. This is evidence that population activity of temporal cortex and parietal cortex shows enhanced coherence during presentation of semantic entities. Coherent activity in this low-frequency range might play a role for binding of multimodal ensembles.

Auditory Perception↗
PubMed1999

Artifact processing in computerized analysis of sleep EEG - a review.

Quantitative analysis of sleep EEG data can provide valuable additional information in sleep research. However, analysis of data contaminated by artifacts can lead to spurious results. Thus, the first step in realizing an automatic sleep analysis system is the implementation of a reliable and valid artifact processing strategy. This strategy should include: (1) high-quality recording techniques in order to minimize the occurrence of avoidable artifacts (e.g. technical artifacts); (2) artifact minimization procedures in order to minimize the loss of data by estimating the contribution of different artifacts in the EEG recordings, thus allowing the calculation of the 'corrected' EEG (e.g. ocular and ECG interference), and finally (3) artifact identification procedures in order to define epochs contaminated by remaining artifacts (e.g. movement and muscle artifacts). Therefore, after a short description of the types of artifacts in the sleep EEG and some typical examples obtained in different sleep stages, artifact minimization and identification procedures will be reviewed.

Artifacts↗
PubMed1998

Low frontal electroencephalographic coherence in neuroleptic-free schizophrenic patients.

BACKGROUND: Electroencephalographic (EEG) coherence analysis is a noninvasive technique for studying corticocortical associations. As there is evidence for a dysfunction of the prefrontal dorsolateral cortex in schizophrenia, we hypothesized to find lower frontal EEG coherence in schizophrenia. METHODS: EEG amplitude and coherence analysis was performed in 16 antipsychotic-free schizophrenic patients and 16 healthy controls. EEG recordings were done with 19 gold-plated electrodes placed according to the International 10/20 system against averaged signals from both earlobes. Local coherence was computed for 22 adjacent electrode pairs within the hemispheres and interhemispheric coherence for eight corresponding electrode pairs of both hemispheres in the delta, theta, alpha, and beta-I band. RESULTS: Amplitude and interhemispheric coherence analysis revealed no differences. Local EEG coherence was significantly lower in schizophrenic patients for Fpl-F7 in the delta (p = .001) and the theta band (p = .002), and at F7-F3 in the alpha band (p = .002). In the delta band coherence of Fpl-F7 was inversely correlated to the Positive and Negative Syndrome Scale positive symptoms subscore (R = -.74, p = .014). CONCLUSIONS: Assuming that EEG coherence can be used to index functional coupling between brain areas under the electrodes, the low EEG coherence in Fpl-F7 and F7-F3 in schizophrenic patients might reflect impaired information processing in the left dorsolateral prefrontal cortex.

Adult↗
PubMed1998

Synchronization between prefrontal and posterior association cortex during human working memory.

We measured coherence between the electroencephalogram at different scalp sites while human subjects performed delayed response tasks. The tasks required the retention of either verbalizable strings of characters or abstract line drawings. In both types of tasks, a significant enhancement in coherence in the theta range (4-7 Hz) was found between prefrontal and posterior electrodes during 4-s retention intervals. During 6-s perception intervals, far fewer increases in theta coherence were found. Also in other frequency bands, coherence increased; however, the patterns of enhancement made a relevance for working memory processes seem unlikely. Our results suggest that working memory involves synchronization between prefrontal and posterior association cortex by phase-locked, low frequency (4-7 Hz) brain activity.

Cerebral Cortex↗
PubMed1998

EEG coherence and reference signals: experimental results and mathematical explanations.

Coherence has become an essential tool in the description of functional relationships between EEG signals generated within various brain areas. In EEG coherence analysis, the reference signal has an important influence, as an improper reference can distort the results and make them impossible to interpret. In the study, EEG are recorded from one volunteer in 11 sessions, with electrodes selected according to the international 10-20 system against FCz. Additional electrodes are placed on the nose, chin and left and right ear lobes, and recordings are made also against FCz. This enables re-referencing of the stored EEG signals for different reference sites, averaged reference signals, common average reference, Laplacian and bipolar. Coherence values using single reference electrodes depend on the reference site to a large extent. Reliable results are obtained using averaged non-cephalic signals as reference ([A1 + A2]/2). Coherence based on FCz yields slightly lower or higher values than that based on non-cephalic reference sites. Completely different results yield common average reference recordings, Laplacian and bipolar recordings, probably owing to the cancellation effect of essential signal portions using these techniques. A mathematical model for coherence based on signal-to-noise ratios is introduced to explain the experimental findings: the model demonstrates that noisy reference signals lead to coherence increase, whereas a coherent amount in the reference signal leads to coherence decrease.

Adult↗
PubMed1998

Topology of EEG coherence changes may reflect differential neural network activation in cold and pain perception.

Pain perception in the brain can be analyzed by neuroimaging (PET, fMRI) and electrophysiological parameter mapping (EEG, ERP/MEG, MEF). These studies have generally been focused on the localization of cerebral activation. Whether pain can be conceptualized as localized function or best be understood by distributed function is important to the theory of human pain processing in the brain. Here, we report that cold and pain perception in the brain is characterized by webs of EEG coherence changes which may reflect coupling or de-coupling of different cortical areas during cold and pain processing. EEG was recorded during cold and pain perception (right hand immersion in 15 degrees C cool-water vs. 0.3 degrees C ice-water for 3 min.) with eyes opened. Subjects rated the cold perception at 2.3 (cool to cold, but no pain) and the pain perception at 6.7 (moderate-strong pain) in a 1-10 scale. The obtained EEG spectral parameters were compared with the corresponding parameters of the resting baseline using paired Wilcoxon tests in the sense of statistical filters to depict those differences which differ clearly from changes by chance. The results were presented in probability maps. The EEG results indicated highly differential coherence networks between cold and pain perception. The cold perception was characterized as decreased coherence in the theta band mainly between frontal electrodes and increased interhemispheric coherence in the alpha range mainly between central and frontal positions. During pain perception almost no coherence changes in the theta band were observed, but great coherence increase in the delta band between central, parietal and frontal electrodes. The network of coherence changes in the alpha band showed strong involvement of electrode C3 concerning coherence increases with frontal positions. In the beta-1 band coherence increase within the left hemisphere was much more pronounced during pain than during cold. The differential characteristics of EEG coherence changes based on neural networks and their spatial organization in the neocortex indicate the distributed brain processing between cold and pain perception in man. This study may contribute to our understanding of the large scale neural networks in cognition based on neurophysiological binding hypothesis and network connections of neural ensembles.

Adult↗
PubMed1998

Left frontal EEG coherence reflects modality independent language processes.

Previous studies showed that distinct components of higher cognitive processes like memorizing of words could be correlated with changes in different frequency bands of the human EEG. This study was designed in order to find out if 1) some frequency bands show power and coherence changes only due to the modality of presented stimuli (either auditory or visual) and 2) if other frequency bands show modality independent effects which should reflect real cognitive-linguistic differences between word classes (either concrete and abstract nouns). EEG was recorded from sixteen right-handed females which had to memorize auditorily and visually presented concrete and abstract nouns. Results show the alpha-1 band to reveal no differences between word classes but demonstrate an influence of modality of stimulus presentation. The only modality independent differences between concrete and abstract noun processing were found in the delta, theta and beta-1 band at left frontal electrodes.

Alpha Rhythm↗
PubMed1997

Persistent patterns of brain activity: an EEG coherence study of the positive effect of music on spatial-temporal reasoning.

Motivated by predictions from the structured trion model of the cortex, behavioral experiments have demonstrated a causal short-term enhancement of spatial-temporal reasoning in college students following exposure to a Mozart sonata, but not in control conditions. The coherence analysis of electroencephalogram (EEG) recordings is well suited to the neurophysiological investigation of this behavioral enhancement. Here we report the presence of right frontal and left temporo-parietal coherent activity induced by listening to Mozart which carried over into the spatial-temporal tasks in three of our seven subjects. This carry-over effect was compared to EEG coherence analysis of spatial-temporal-tasks after listening to text. We suggest that these EEG coherence results provide the beginnings of understanding of the neurophysiological basis of the causal enhancement of spatial-temporal reasoning by listening to specific music. The observed long-lasting coherent EEG pattern might be evidence for structured sequences in cortical dynamics which extend over minutes.

Adult↗
PubMed1996

EEG coherence within the 13-18 Hz band as a correlate of a distinct lexical organisation of concrete and abstract nouns in humans.

Coherence analysis was applied to the EEG of 19 female participants who had to memorize auditorily presented abstract and concrete nouns. The EEG was recorded from 19 scalp electrodes (10/20 system). Significant differences between both word classes were found only in the beta 1-band (13-18 Hz) whereas the alpha 1-band (8-10 Hz) revealed coherence patterns which were identical for both word classes. These results indicate that the alpha 1-band reflects cognitive processes that were common to both word classes, whereas the beta 1-band seems to be closely related to associative processes and more complex cognitive functions.

Brain↗
PubMed1995

[EEG changes in schizophrenic diseases--a critical review].

To identify specific changes in the electroencephalogram of schizophrenic patients has been an important target of clinical neurophysiology ever since the introduction of the EEG. Results of EEG-amplitude- and frequency-analysis in schizophrenics--although sometimes contradictory--are presented. Special emphasis is laid upon possible clinical applicabilities, for instance the prediction of the clinical course by means of neurophysiological changes after administration of a neuroleptic test dose. Finally, the usefulness of examining electrophysiological changes in such a heterogeneous group, as schizophrenics are, is discussed critically.

Antipsychotic Agents↗
PubMed1994

Calculation of event-related coherence--a new method to study short-lasting coupling between brain areas.

This article deals with the estimation of event-related coherence (ERCoh) and its application to the planning and execution of self-paced index finger movement. ERCoh estimation complements the event-related desynchronization (ERD) measurements of rhythms within the alpha band. ERCoh yields information of the functional relationships between different brain areas as a function of time. The time resolution is 125 msec. Before movement onset a contralateral ERCoh increase was found between premotor and motor areas. This coherence increase was accompanied by an ERCoh decrease in parallel to the ERD over the contralateral centro-temporal areas. During movement, the ERD became bilaterally symmetrical. Simultaneously, interhemispheric coherence between contralateral and ipsilateral sensori-motor areas increased.

Brain↗