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Biomedical subjects

F Pulvermüller

Publications and source records attributed to F Pulvermüller.

At least 19 recordsLinked to original sources
PubMed1997

Fractal dimensions of short EEG time series in humans.

Fractal dimensions has been proposed as a useful measure for the characterisation of electrophysiological time series. But one of the problems of this approach, is the difficulty to record time series long enough of determine the 'real' fractal dimension. Nevertheless it is possible to calculate fractal dimensions for very short data-segments. Using time series of different length it is possible to show, that there is a monotoneous relation between fractal dimension and the number of data-points. This relation could be further interpreted with the help of an extrapolation scheme. In addition this effect is also seen with surrogate data, generated from that signal. We conclude that it is feasible to use fractal dimension as a tool to characterise the complexity for short electroencephalographic (EEG) time series, but it is not possible to decide whether the brain is a chaotic system or not.

Electroencephalography↗
PubMed1997

Short-term effects of behavioral treatment on movement initiation and postural control in Parkinson's disease: a controlled clinical study.

In a controlled clinical study, we investigated the effects of behavioral treatment on postural and gait initiation problems idiopathic Parkinson's disease (PD). Comparable groups of patients received therapy (experimental group, n = 15) and nonspecific psychological treatment (control group, n = 14) for 10 weeks. We monitored various variables reflecting properties of posture and gait initiation by using an optoelectronic motion analyzer (electronic movement analysis system, ELITE). A clinician blind to group membership of the patients assessed PD severity with the United Parkinson's Disease Rating Scale (UPDRS) before and after the treatment period. ELITE measures of postural stability and movement initiation revealed treatment-specific effects. In addition, UPDRS motor scores showed significant improvement only after behavioral treatment. We conclude that behavioral treatment in Parkinson's disease may improve motor disabilities in moderately advanced PD patients.

Aged↗
PubMed1997

High-frequency brain activity: its possible role in attention, perception and language processing.

Coherent high-frequency neuronal activity has been proposed as a physiological indicator of perceptual and higher cognitive processes. Some of these processes can only be investigated in humans and the use of non-invasive recording techniques appears to be a prerequisite for investigating their physiological substrate in the healthy human brain. After addressing methodological issues in the non-invasive recording of high-frequency responses, we summarize studies indicating co-occurrence of neuronal synchrony of single cells exhibiting rhythmic activity at high frequencies, oscillations in the local field potential and dynamics in high frequencies recorded using high-resolution electroencephalography (EEG) and magnetoencephalography (MEG). We then review EEG and MEG studies of attention, perception, and language processing in humans indicating that dynamics in the high-frequency range > 20 Hz reflect specific cognitive processes. Types of high-frequency (HF) activity can be distinguished according to their latency after stimulus onset, stimulus-locking, cortical topography and frequency. There appears to be a systematic relationship between specific cognitive processes and types of HF activity. The findings are related to recent theories about the generation of HF activity and their possible role in binding of stimulus features. Dynamics of HF cortical activity reflecting higher cognitive processes can be accounted for based on the assumption that the elements of cognitive processing, e.g. visual objects and words, are organized in the brain as distributed neuronal assemblies with defined cortical topographies generating well-timed spatio-temporal activity patterns.

Arousal↗
PubMed1996

High-frequency cortical responses reflect lexical processing: an MEG study.

Meaningful words and matched pseudowords, such as moon vs. noom, are of equal perceptual complexity, but invoke different cognitive processes. To investigate high-frequency cortical responses to these stimuli, biomagnetic signals were recorded simultaneously over both hemispheres of right-handed individuals listening to words and pseudowords. Consistent with earlier EEG studies, evoked spectral responses recorded from the left hemisphere revealed depression of spectral power in the low gamma band (around 30 Hz) after pseudowords but not after words. Similar differences between stimulus categories were present in the beta range. These results indicate that distinct patterns of high-frequency cortical responses correspond to the different cognitive processes invoked by words and pseudowords. It is hypothesized that differential high-frequency cortical responses signal the activation or activation failure of distributed Hebbian cell assemblies representing words and other elements of cognitive processing.

Adult↗
PubMed1996

P3 and contingent negative variation in Parkinson's disease.

Patients with idiopathic Parkinson's syndrome, most of them in early stages of the disease, and matched healthy controls participated in a continuous performance task while their EEGs were recorded from 15 electrodes. During preparation of movements, a contingent negative variation (CNV) maximal at central and posterior sites was visible. This CNV was reduced in the patient population. A large P3-like positive deflection occurred after go and no-go stimuli that called for execution (go) or suppression (no-go) of a button press. Compared to healthy controls, the positive wave in Parkinson patients was significantly reduced after go stimuli and maximally attenuated when no-go stimuli had indicated to suppress the motor response. In contrast, P3 amplitudes after irrelevant "ignore' stimuli was not significantly reduced in the patients. These results are interpreted in the framework of a model of striatal function postulating (i) that populations of cortical and striatal neurons form distributed functional units (Hebbian cell assemblies), and (ii) that mutual inhibition between such cortico-striatal cell assemblies is mediated by the neostriatum, the forebrain structure primarily affected in Parkinson's disease.

Behavior↗
PubMed1996

Multiple simultaneous stimulus presentation facilitates lexical processing.

Bilateral presentation of two copies of the same word leads to faster lexical decisions compared to unilateral presentation alone (bilateral gain). This has implications for theories of interhemispheric interaction, because it suggests that, under certain conditions, both hemispheres cooperate rather than inhibit each other or act independently. Experiment 1 confirmed that the bilateral gain is word-specific and does not occur for pseudowords. Whereas the bilateral gain proved to be present for words of different word frequencies, results of Experiment 2 suggest that it is slightly stronger for high-frequency words compared to words of lower frequencies. Experiment 3 revealed that higher numbers of stimuli (two versus four copies of the same word/pseudoword) presented at the same time lead to an additional improvement of word processing. These results support a neurobiological model of word representation assuming that words are cortically represented in widely distributed interhemispheric cell assemblies. Summation of activity in such assemblies leads to faster and more reliable ignition of the network.

Adult↗
PubMed1996

The concept of transcortical cell assemblies: a key to the understanding of cortical lateralization and interhemispheric interaction.

According to Hebb, elements of higher cognitive processes, such as concepts, words and mental images, are realized in the brain as cortical cell assemblies, i.e. large and strongly connected neuron populations that form functional units. Neurons belonging to such assemblies may be scattered over wide cortical areas, and some cell assemblies may even comprise neurons of both hemispheres (transcortical assemblies). If full activation (ignition) of an assembly leads to fast circulation of neuronal activity in the assembly, this process should be visible in high-frequency cortical responses. Some evidence will be reviewed that cell assembly ignition indeed leads to changes in high-frequency cortical responses which can be recorded in the EEG and MEG. Within the cell assembly-framework, the question of cortical laterality translates into the question of how neurons of transcortical assemblies are balanced between the hemispheres. This approach allows for different degrees of laterality. Recent evidence is summarized that the degree of laterality indeed differs between language units. For example, the cortical representation of certain words appears to be strongly lateralized to the left hemisphere while those of others are less lateralized. If neurons of both hemispheres are part of one assembly bihemispheric processing should lead to a processing advantage compared to processing in the dominant hemisphere alone. The latter appears to be the case for lexical processing, as revealed by recent behavioral studies. In conclusion, the cell assembly-framework suggests a more fine-grained description of the issue of cortical laterality; it is not appropriate to ask whether "modules" supporting higher cortical functions are located either in the left or right hemisphere. Rather, it appears fruitful to ask how the neurons of transcortical cell assemblies are balanced between the hemispheres.

Brain Mapping↗
PubMed1996

Hebb's concept of cell assemblies and the psychophysiology of word processing.

Hebb's brain-theoretical approach suggests that tightly connected networks of neurons, Hebbian cell assemblies, are the building blocks of cognitive functions. These assemblies are not necessarily restricted to a small cortical locus but may be dispersed over distant cortical areas. Assemblies with different topographies can be postulated for different kinds of words, such as meaningful content versus grammatical function words or words eliciting motor versus visual associations. Evidence from evoked potentials and gamma-band electrocortical responses elicited by lexical material supports a cell assembly model of language and other higher cognitive functions.

Brain↗
PubMed1996

Cortical correlates of semantic classical conditioning.

Event-related potentials to visually displayed pseudowords were registered from 13 individuals. In a differential conditioning paradigm, half of the pseudowords had previously been paired with a painful electric shock (shock words) and the other half had been presented without shock (nonshock words). Participants were asked to decide if the words had been presented during the conditioning phase or not. Larger N100 amplitudes and a more negative-going slow wave 400-800 ms after word presentation were found for shock as compared with nonshock words. This effect was stronger over the left than over the right hemisphere. This left-lateralized negativity might reflect the activation of a cell assembly representing the memory of the learned word-shock contingency. Furthermore, the increased N100 amplitude elicited by shock as compared with nonshock words may be interpreted as an increased attentive facilitation for aversive pain-related information as a consequence of conditioning.

Adult↗
PubMed1995

Spectral responses in the gamma-band: physiological signs of higher cognitive processes?

It has recently been proposed that brain responses in the gamma-range (> 20 Hz) include information about specific cognitive processes in the human brain. Empirical data substantiating this assumption come from EEG and MEG recordings during visual and language processing. For example, 30 Hz activity has been found to be stronger during processing of words than during processing of meaningless but pronounceable pseudo-words. However, it has been reported that power changes in the gamma-band are sometimes artefacts of changes taking place in other frequencies, such as the alpha-band. In this study, we investigated power changes in frequency bands outside the gamma-range and found no evidence that such changes are related to the dynamics in gamma-power distinguishing between words and pseudowords. These results are consistent with the view that gamma-band responses are an indicator of lexical processing and other cognitive processes related to binding of stimulus features into a whole (Gestalt), as proposed by Singer.

Acoustic Stimulation↗
PubMed1995

Evoked potentials distinguish between nouns and verbs.

Electrocortical correlates of the processing of nouns and verbs were recorded in 32 healthy individuals performing lexical decisions. Analyses of EEG data recorded through 29 channels revealed different topographies of cortical activity evoked by nouns and verbs. Differences were most pronounced at recording sites over the frontal lobes. The stronger motor associations elicited by verbs as measured pre-experimentally seem to be responsible for the topographical differences of event related brain potentials to verbs and nouns. In agreement with recent evidence from brain-damaged subjects, these results provide evidence that (1) nouns and verbs have distinct neural generators and that (2) these generators involve areas outside the classical language regions of the brain.

Cerebral Cortex↗
PubMed1995

Motor programming in both hemispheres: an EEG study of the human brain.

Differential hemispheric involvement in controlling simple and complex motor movements was investigated in humans using EEG spectral responses. Analysis of spectral power in the alpha band revealed the following. While during a simple motor task (tapping) signs of unilateral cortical activation were present, more complex sequential motor behaviour (Luria finger apposition task) led to symmetrical bihemispheric activation. It appears that unilateral cortical processing is present in the normal brain when very simple computations are performed. Bilateral hemispheric activity and interhemispheric interaction may be general features of more complex information processing in the cortex.

Brain↗
PubMed1995

Visual stimulation alters local 40-Hz responses in humans: an EEG-study.

Irregular changing visual patterns and coherently moving bars were presented either in the upper or lower half of the visual field of 12 human subjects. EEG responses recorded over the occipital lobe showed an increase of 40 Hz spectral power when a regular pattern of moving bars appeared. This enhancement of 40-Hz activity varied as a function of visual field presentation. Coherent stimuli in the upper visual field elicited 40-Hz enhancement at lower occipital electrodes, while coherent stimulation in the lower visual field elicited 40-Hz enhancement at upper occipital electrodes. These results evidence that neuronal 40-Hz responses are a correlate of perception of coherent visual patterns in humans. Area-specific 40-Hz responses related to visual perception can be picked up in the EEG.

Adult↗
PubMed1995

Fractal dimension of electroencephalographic time series and underlying brain processes.

Fractal dimension has been proposed as a useful measure for the characterization of electrophysiological time series. This paper investigates what the pointwise dimension of electroencephalographic (EEG) time series can reveal about underlying neuronal generators. The following theoretical assumptions concerning brain function were made (i) within the cortex, strongly coupled neural assemblies exist which oscillate at certain frequencies when they are active, (ii) several such assemblies can oscillate at a time, and (iii) activity flow between assemblies is minimal. If these assumptions are made, cortical activity can be considered as the weighted sum of a finite number of oscillations (plus noise). It is shown that the correlation dimension of finite time series generated by multiple oscillators increases monotonically with the number of oscillators. Furthermore, it is shown that a reliable estimate of the pointwise dimension of the raw EEG signal can be calculated from a time series as short as a few seconds. These results indicate that (i) The pointwise dimension of the EEG allows conclusions regarding the number of independently oscillating networks in the cortex, and (ii) a reliable estimate of the pointwise dimension of the EEG is possible on the basis of short raw signals.

Brain↗
PubMed1995

Electrocortical distinction of vocabulary types.

Psycholinguistic theories propose that words of the 2 major vocabulary classes, content (open-class) and function (closed-class) words, are computationally distinct and have different neuronal generators. This predicts distinct EEG patterns elicited by words of these 2 classes. To test this prediction, content and function words, together with matched pseudowords, were presented in a lexical decision task (where subjects had to decide whether stimuli were meaningful words or not). Evoked potentials were recorded from 17 electrodes 12 of which were located in close vicinity of the perisylvian cortices. Already 160 msec post stimulus onset, substantial differences in activity patterns distinguish the 2 vocabulary classes. A hemisphere by word class interaction revealed interhemispheric differences for function words but not for content words. Potentials evoked by function words were more negative over the left hemisphere compared to the right. These results evidence that brain mechanisms underlying function and content word processing are different. The following explanation of the data is proposed: content words correspond to neuronal assemblies equally distributed over both hemispheres, while assemblies corresponding to function words are strongly lateralized to the left hemisphere and primarily located in the perisylvian region.

Adult↗
PubMed1995

[Neurobiology of language processing].

Neurobiological mechanisms underlying language functions can be modeled in the framework of Hebb's cell assembly theory. According to this approach, meaningful words, but not meaningless pseudowords, have a cortical representation in strongly coupled ensembles of neurons distributed over wide cortical areas. Cell assemblies with different cortical topographies can be assumed for different word types. These hypotheses give rise to empirical predictions that can be tested in behavioral and electrophysiological experiments with healthy and neurologically impaired subjects. Results of a series of experiments providing support for the above assumptions are summarized.

Brain Mapping↗
PubMed1994

Interhemispheric cooperation during lexical processing is mediated by the corpus callosum: evidence from the split-brain.

If two copies of a meaningful word are tachistoscopically presented simultaneously in both visual half-fields of normal subjects the word will be processed more rapidly and more accurately compared to unilateral presentation (bilateral gain). The word-specific bilateral gain may be due to excitatory transcallosal connections within interhemispheric cell assemblies corresponding to words. In this case, the bilateral gain should be absent in split-brain patients. L.B., a split-brain patient, performed a lexical decision task with words and non-words presented in the left visual field, the right visual field, or in both visual fields simultaneously. As predicted, bilateral presentations did not improve performance compared to unilateral presentation in the right visual field. This result suggests that transcallosal connections play a significant role in lexical processing.

Adult↗