Biomedical subjects

Friedemann Pulvermüller

Publications and source records attributed to Friedemann Pulvermüller.

30 records · Page 2Linked to original sources

PubMed2004

Neurophysiological correlates of word and pseudo-word processing in well-recovered aphasics and patients with right-hemispheric stroke.

Neurophysiological correlates of language recovery after stroke were investigated. Neurological patients with single focal lesions in their left or right hemisphere and healthy control subjects made lexical decisions on written words and pseudo-words while EEG responses were recorded. At the time of testing, patients did not show clinically apparent language dysfunction, although those with left-hemisphere lesions had suffered from aphasia in the first months after their stroke. A P3-like positive deflection of the event-related potential (ERP) was reduced in the patients relative to healthy controls, this reduction being most pronounced over the hemisphere affected by stroke. Consistent with earlier research, healthy control subjects showed more positive ERPs to words than to pseudo-words. This pattern was reversed in both patient groups, where words elicited more negative-going ERPs than pseudo-words already 160-320 ms after stimulus onset. Because ERPs showed between-group differences only for words, these word-specific neurophysiological signatures altered in stroke patients with well-recovered language functions may be a correlate of cortical lesions or an index of reorganization of language after stroke.

Adult↗

PubMed2003

Grammar processing outside the focus of attention: an MEG study.

To address the cerebral processing of grammar, we used whole-head high-density magnetoencephalography to record the brain's magnetic fields elicited by grammatically correct and incorrect auditory stimuli in the absence of directed attention to the stimulation. The stimuli were minimal short phrases of the Finnish language differing only in one single phoneme (word-final inflectional affix), which rendered them as either grammatical or ungrammatical. Acoustic and lexical differences were controlled for by using an orthogonal design in which the phoneme's effect on grammaticality was inverted. We found that occasional syntactically incorrect stimuli elicited larger mismatch negativity (MMN) responses than correct phrases. The MMN was earlier proposed as an index of preattentive automatic speech processing. Therefore, its modulation by grammaticality under nonattend conditions suggests that early syntax processing in the human brain may take place outside the focus of attention. Source analysis (single-dipole models and minimum-norm current estimates) indicated grammaticality dependent differential activation of the left superior temporal cortex suggesting that this brain structure may play an important role in such automatic grammar processing.

Acoustic Stimulation↗

PubMed2003

Early influences of word length and frequency: a group study using MEG.

In what way are linguistic word properties reflected in the neurophysiological brain response? During a memory task we presented written words orthogonally varied in length (long, short) and frequency (high, low). Brain responses of 15 subjects were recorded using a 148-channel magnetoencephalogram. Very early after stimulus onset (60 ms), long words led to significantly stronger activation than short words, as revealed by the global field power (GFP). Later on, low frequency words led to stronger brain responses than high frequency words. This effect depended on word length: it was seen 120-170 ms after stimulus onset, for short words only, but at 225-250 ms exclusively for long words. Source localisation revealed that effects due to word length were pronounced over occipital areas whereas frequency effected more widespread cortical areas with a strong focus over left occipitotemporal areas (visual word form areas).

Adolescent↗

PubMed2003

Word-category specific deficits after lesions in the right hemisphere.

A speeded lexical decision task was used to investigate word-category deficits in patients suffering from lesions in the right hemisphere and in neurological controls without cortical lesion. In all patients from one group (n = 12), the right frontal lobe was affected causing a left-sided hemiparesis. In the second group (n = 6), lesions primarily affected areas in the right inferior temporo-occipital lobes. Patients with motor deficits due to lesions in the spinal cord or in the periphery served as neurological controls (n = 9). Processing of three categories of words was investigated: verbs referring to actions (action verbs (acVs)); nouns with strong visual associations (visually-related nouns (viNs)); and nouns with both strong action and visual associations (bimodal nouns (biNs)). Stimulus categories were matched for word length and normalized lexical frequency. Error scores revealed a significant word category by patient group interaction. Patients with lesions in the right frontal lobe showed most severe deficits in processing action verbs, whereas those with lesions in their right temporo-occipital areas showed most severe deficits in processing visually-related nouns. Neurological controls did not show any differences between word categories. The double dissociation of the processing impairments seen in frontal versus temporo-occipital patients demonstrates that specific word-category deficits can arise from lesions in the right non-dominant hemisphere. An account for these results in terms of distributed neuronal systems representing words is offered.

Adult↗

PubMed2003

Complexity of visual stimuli and non-linear EEG dynamics in humans.

The effects of stimulus complexity on the nonlinear electrical brain (EEG) dynamics were investigated in a sample of 24 healthy volunteers. Stimuli used were either a single mechanical low-friction pendulum with a periodic movement (temporal frequency about 1 Hz) or a double-pendulum with a chaotic movement, which were observed for 2-3 min in each case. The prediction that a more complex visual stimulus (double-pendulum) increases the dimensional complexity of brain activity as compared to a simple visual stimulus (single-pendulum), was confirmed by determination of pointwise correlation dimension. Further, there was a significant decrease of alpha power in the double-pendulum compared to a single-pendulum condition. Moreover, a correlation analysis showed a positive correlation between EEG complexity and beta power over the whole cortex in the single- and, above all, in the double-pendulum condition, and also a positive correlation between dimensional complexity and alpha power in the double-pendulum condition only, particularly in the brain regions responsible for the 'bottom-up' sustained attention processes.

Adult↗

PubMed2003

Automatic processing of grammar in the human brain as revealed by the mismatch negativity.

The Mismatch Negativity (MMN), a neurophysiological indicator of cognitive processing, was used to investigate grammatical processes in the absence of focused attention to language. Subjects instructed to watch a silent video film and to ignore speech stimuli heard grammatical and ungrammatical spoken word strings that were physically identical up to a divergence point where they differed between each other by a minimal acoustic event, the presence or the absence of a final -s sound. The sentence we come was presented as a rare deviant stimulus against the background of frequently occurring ungrammatical strings, and, in a different experiment, the ungrammatical string *we comes was the deviant in the reverse design. To control for effects related to differences between the critical words, come and comes, control conditions were used in which the same words were presented out of linguistic context. At 100-150 ms after the divergence point, the ungrammatical deviant stimulus elicited a larger MMN than the correct sentence at left-anterior recording sites. This difference was not seen under the out-of-context conditions. In the time range 100-400 ms after stimulus divergence, a spatiotemporal pattern of grammatically related effects was documented by statistically significant interactions of the word and context variables. Minimum-Norm Current Estimates of the cortical sources of the grammaticality effects revealed a main source in the left frontal cortex. We use a neurobiological model of serial order processing to provide a tentative explanation for the data.

Acoustic Stimulation↗

PubMed2003

Spatiotemporal dynamics of neural language processing: an MEG study using minimum-norm current estimates.

The inferior frontal and superior temporal areas in the left hemisphere are well-known to be crucial for language processing in most right-handed individuals. This has been established by classical neurological investigations and neuropsychological studies along with metabolic brain imaging have recently revealed converging evidence. Here, we use fast neurophysiological brain imaging, magnetoencephalography (MEG), and L1 Minimum-Norm Current Estimates to investigate the time course of cortical activation underlying the magnetic Mismatch Negativity elicited by a spoken word. Left superior-temporal areas became active 136 ms after the information in the acoustic input was sufficient for identifying the word, and activation of the left inferior-frontal cortex followed after an additional delay of 22 ms. By providing answers to the where- and when-questions of cortical activation, MEG recordings paired with current estimates of the underlying cortical sources may advance our understanding of the spatiotemporal dynamics of distributed neuronal networks involved in cognitive processing in the human brain.

Adult↗

PubMed2002

Neurophysiological evidence of memory traces for words in the human brain.

Mismatch negativity (MMN), an index of experience-dependent memory traces, was used to investigate the processing of lexical contrasts in the human brain. The MMN was elicited either by rare words presented among repetitive words or pseudowords, or by pseudowords presented among words. Phonetic and phonological contrasts were identical in all conditions. MMNs elicited by both word deviants were larger than that elicited by the deviant pseudoword. The presence of lexical contrast did not significantly alter the word-elicited MMNs, which were, however, distinct in amplitude and topography from the MMN evoked by pseudowords. Thus, our results indicate the existence of word-related MMN enhancement largely independent of the lexical status of the standard stimulus. This enhancement may reflect the presence of a long-term memory trace for a spoken word.

Acoustic Stimulation↗

PubMed2002

A brain perspective on language mechanisms: from discrete neuronal ensembles to serial order.

Language is constituted by discrete building blocks, sounds and words, which can be concatenated according to serial order principles. The neurobiological organization of these building blocks, in particular words, has been illuminated by recent metabolic and neurophysiological imaging studies. When humans process words of different kinds, various sets of cortical areas have been found to become active differentially. The old concept of two language centers processing all words alike must therefore be replaced by a model according to which words are organized as discrete distributed neuron ensembles that differ in their cortical topographies. The meaning of a word, more precisely, aspects of its reference, may be crucial for determining which set of cortical areas becomes involved in its processing. Whereas the serial order of sounds constituting a word may be established by serially aligned sets of neurons called synfire chains, different mechanisms are necessary for establishing word order in sentences. The serial order of words may be organized by higher-order neuronal sets, called sequence detectors here, which are being activated by sequential excitation of neuronal sets representing words. Sets of sequence detectors are proposed to process aspects of the syntactic information contained in a sentence. Other syntactic rules can be related to general features of the dynamics of cortical activation and deactivation. These postulates about the brain mechanisms of language, which are rooted in principles known from neuroanatomy and neurophysiology, may provide a framework for theory-driven neuroscientific research on language.

Brain↗

PubMed2002

Redundancy gains and costs in cognitive processing: effects of short stimulus onset asynchronies.

In 7 experiments, the influence of varying stimulus onset asynchronies (SOAs) on the processing of redundant information about words and pseudowords was investigated. All stimuli were visually presented once or twice with 2 copies of the same item flashed either simultaneously or with short SOAs between presentations. The experiments revealed a redundancy gain for words that was absent for pseudowords. Furthermore, the redundancy gain disappeared at an SOA of 50 ms, and there was a gradual performance decline at longer SOAs. However, probing SOAs of 150 and 300 ms revealed that, compared with presentation of 1 target stimulus alone, words were processed significantly faster when target and redundantcopy appeared with a 150-ms lag. The results are tentatively explained in a neurocognitive framework.

Adult↗

PubMed2002

Memory traces for inflectional affixes as shown by mismatch negativity.

Mismatch negativity (MMN), an index of experience-dependent memory traces, was used to investigate the processing of grammatical affixes in the human brain. The MMN was elicited by either a verb stem or an inflected verb form, phonetic contrasts being identical in both conditions. The topography of the mismatch responses showed clear left-hemispheric laterality in both conditions. However, the MMN to the inflected form occurred later than that for the stem. Furthermore, the inflected stimulus produced MMN maximal in centroparietal sites, whereas stem-elicited MMN was more profound at more frontal sites. We suggest that these features of the MMN to inflected form indicate delayed activation of left-lateralized perisylvian cell assemblies that function as cortical memory traces of inflectional affixes.

Acoustic Stimulation↗

PubMed2001

Brain reflections of words and their meaning.

The neurobiological organization of meaningful language units, morphemes and words, has been illuminated by recent metabolic and neurophysiological imaging studies. When humans process words from different categories, sets of cortical areas become active differentially. The meaning of a word, more precisely aspects of its reference, may be crucial for determining which set of cortical areas is involved in its processing. Word-related neuron webs with specific cortical distributions might underlie the observed category-specific differences in brain activity. Neuroscientific principles can explain these differential topographies.

Journal Article↗