Biomedical subjects

F Pulvermüller

Publications and source records attributed to F Pulvermüller.

47 records · Page 3Linked to original sources

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↗

PubMed1994

Words and pseudowords elicit distinct patterns of 30-Hz EEG responses in humans.

Meaningful words, such as moon, and physically similar but meaningless pseudowords, such as noom, were presented visually in a lexical decision task. The EEG was recorded from 17 scalp electrodes. Significant differences between both stimulus classes were observed in evoked spectral responses of the 'gamma-band' approximately 30 Hz. A hemisphere by wordness interaction demonstrated that 30-Hz spectral power over the left hemisphere was reduced after pseudowords only. These results indicate that gamma-band responses reflect the different cognitive processes induced by words and pseudowords. A possible explanation is the following. Synchronous activation of large cortical cell assemblies takes place after word presentation but not after presentation of pseudowords.

Brain↗

PubMed1994

Lexical decision after left, right and bilateral presentation of function words, content words and non-words: evidence for interhemispheric interaction.

Function words, content words and pronounceable non-words (pseudowords) were presented tachistoscopically either in the left or the right visual field or with identical copies flashed simultaneously to both visual half-fields. Consistent with earlier studies [10], function words were found to show a right visual field advantage, whereas for content words the right visual field advantage was absent. Compared to either of the unilateral modes of presentation, bilateral presentation of identical word stimuli improved accuracy and latency significantly. The bilateral (Bi) advantage was largest for content words, and was also highly significant for function words in both latency and accuracy. The Bi gain was absent for non-words (significant interaction of Wordness x Visual Field). These results indicate that the lexicons of the left and right hemisphere can "collaborate" rather than inhibit each other or act independently when processing the same linguistic stimuli. Our findings are consistent with the view that the neuronal counterparts of words are Hebbian cell assemblies consisting of strongly connected excitatory neurons of both hemispheres. Since function words show a right visual field advantage in addition to their Bi gain, their assemblies are likely to have most of their neurons located in the left hemisphere. Neuronal assemblies corresponding to content words may be less strongly lateralized.

Adolescent↗

PubMed1993

Behavioral and neuronal changes during treatment of mixed transcortical aphasia: a case study.

The development of language mechanisms outside the traditional language regions is evidenced by the case of K.S., a patient with chronic mixed transcortical aphasia, that is, good repetition performance compared to all other language abilities. The aphasia was caused by an infarction of the left a. carotis interna that completely destroyed the left perisylvian language region and adjacent structures. Five years post onset the patient underwent intensive aphasia therapy. In the treatment setting chosen, both speech production and comprehension abilities improved as demonstrated by adequacy and reaction time scores. It is argued that the behavioral changes observed are likely to be due to (a) newly acquired communicative strategies and (b) neuronal changes within K.S.'s brain. The behavioral changes are explained in terms of strengthening of synaptic connections and formation of Hebbian cell assemblies corresponding to words.

Aged↗

PubMed1992

[Model of a neurological theory of speech].

Recently, theories of neuronal computation in the brain have become detailed enough, so that it becomes possible to speculate about mechanisms underlying the production and perception of language. How many neurons are involved when we utter, or understand, a word, a phoneme, a phrase? In what neuronal form are the rules of grammar laid down in the synaptic network? To what does a morpheme correspond in the brain?

Aphasia↗

PubMed1992

[New approaches in speech therapy].

Following a brief introduction of the neurological basis and the localization of aphasias, we discuss approaches to language therapy which are based on linguistic theories. We first sketch principles of language-based therapy. Then we introduce communicative aphasia treatment and explain aspects under which the latter represents an extension of the language-based approach. In order to provide neurological arguments in favour of communicative therapy, we discuss the language theory of Hughlings Jackson. Finally, we give examples for communicative therapy paradigms, for some of which implementation in specific computer training programs is available.

Aphasia↗

PubMedDate not supplied

Nouns and verbs in the intact brain: evidence from event-related potentials and high-frequency cortical responses.

Lesion evidence indicates that words from different lexical categories, such as nouns and verbs, may have different cortical counterparts. In this study, processing of nouns and verbs was investigated in the intact brain using (i) behavioral measures, (ii) stimulus-triggered event-related potentials and (iii) high-frequency electrocortical responses in the gamma band. Nouns and verbs carefully matched for various variables, including word frequency, length, arousal and valence, were presented in a lexical decision task while electrocortical responses were recorded. In addition, information about cognitive processing of these stimuli was obtained using questionnaires and reaction times. As soon as approximately 200 ms after stimulus onset, event-related potentials disclosed electrocortical differences between nouns and verbs over widespread cortical areas. In a later time window, 500-800 ms after stimulus onset, there was a significant difference between high-frequency responses in the 30 Hz range. Difference maps obtained from both event-related potentials and high-frequency responses revealed strong between-category differences of signals recorded above motor and visual cortices. Behavioral data suggest that these different physiological responses are related to semantic associations (motor or visual) elicited by these word groups. Our results are consistent with a neurobiological model of language representation postulating cell assemblies with distinct cortical topographies as biological counterparts of words. Assemblies representing nouns referring to visually perceived objects may include neurons in visual cortices, and assemblies representing action verbs may include additional neurons in motor, premotor and prefrontal cortices. Event-related potentials and high-frequency responses are proposed to indicate two different functional states of cell assemblies: initial full activation ('ignition') and continuous reverberatory activity.

Adult↗