Biomedical subjects

Friedemann Pulvermüller

Publications and source records attributed to Friedemann Pulvermüller.

At least 19 recordsLinked to original sources

PubMed2006

Early semantic context integration and lexical access as revealed by event-related brain potentials.

A late neurophysiological response, the N400, is well known to reflect word processing and semantic context integration. Nevertheless, behavioural and neurophysiological data have demonstrated that word features and semantic sentence context influence linguistic processes already within the first 200 ms following the onset of the critical word stimulus. The lack of early word-related ERP effects in some studies might be due to large stimulus variance on relevant linguistic parameters, for example the length of written words or their frequency of usage. Here we investigated the effect of the length of words, their standardized lexical frequency and probability to occur in a given semantic context, by orthogonally varying these factors in a sentence-reading task. We found word frequency and probability to be reflected neurophysiologically already at 120 and 180 ms after written word onset. However, at these early stages frequency and probability effects were modulated by word length, as documented by significant interactions, whereas at later stages, around 300-500 ms, additive effects of these variables were found. These results indicate that semantic context integration may take place at a surprisingly early stage and near-simultaneously with the processing of information about the form of a word and its lexical properties, therefore challenging serial models of psycholinguistic information access. A methodological implication of this study is that, in order to obtain early psycholinguistic ERP effects, stimulus variance must be kept to a minimum.

Adult↗

PubMed2006

Language models based on Hebbian cell assemblies.

This paper demonstrates how associative neural networks as standard models for Hebbian cell assemblies can be extended to implement language processes in large-scale brain simulations. To this end the classical auto- and hetero-associative paradigms of attractor nets and synfire chains (SFCs) are combined and complemented by conditioned associations as a third principle which allows for the implementation of complex graph-like transition structures between assemblies. We show example simulations of a multiple area network for object-naming, which categorises objects in a visual hierarchy and generates different specific syntactic motor sequences ("words") in response. The formation of cell assemblies due to ongoing plasticity in a multiple area network for word learning is studied afterwards. Simulations show how assemblies can form by means of percolating activity across auditory and motor-related language areas, a process supported by rhythmic, synchronized propagating waves through the network. Simulations further reproduce differences in own EEG&MEG experiments between responses to word- versus non-word stimuli in human subjects.

Animals↗

PubMed2006

Language outside the focus of attention: the mismatch negativity as a tool for studying higher cognitive processes.

Which aspects of language and cognitive processing take place irrespective of whether subjects focus their attention on incoming stimuli and are, in this sense, automatic? The Mismatch Negativity (MMN), a neurophysiological brain response recorded in the EEG and MEG, is elicited by attended and unattended stimuli alike. Recent studies investigating the cognitive processes underlying spoken language processing found that even under attentional withdrawal, MMN size and topography reflect the activation of memory traces for language elements in the human brain. Familiar sounds of one's native language elicit a larger MMN than unfamiliar sounds, and at the level of meaningful language units, words elicit a larger MMN than meaningless pseudowords. This suggests that the MMN reflects the activation of memory networks for language sounds and spoken words. Unattended word stimuli elicit an activation sequence starting in superior-temporal cortex and rapidly progressing to left-inferior-frontal lobe. The spatio-temporal patterns of cortical activation depend on lexical and semantic properties of word stems and affixes, thus indicating that the MMN can give clues about lexico-semantic information processing stored in long term memory. At the syntactic level, MMN size was found to reflect whether a word string conforms to abstract grammatical rules. This growing body of results suggests that lexical, semantic and syntactic information can be processed by the central nervous system outside the focus of attention in a largely automatic manner. Analysis of spatio-temporal patterns of generator activations underlying the MMN to speech may be an important tool for investigating the brain dynamics of spoken language processing and the activated distributed cortical circuits acting at long-term memory traces.

Acoustic Stimulation↗

PubMed2006

Motor cortex maps articulatory features of speech sounds.

The processing of spoken language has been attributed to areas in the superior temporal lobe, where speech stimuli elicit the greatest activation. However, neurobiological and psycholinguistic models have long postulated that knowledge about the articulatory features of individual phonemes has an important role in their perception and in speech comprehension. To probe the possible involvement of specific motor circuits in the speech-perception process, we used event-related functional MRI and presented experimental subjects with spoken syllables, including [p] and [t] sounds, which are produced by movements of the lips or tongue, respectively. Physically similar nonlinguistic signal-correlated noise patterns were used as control stimuli. In localizer experiments, subjects had to silently articulate the same syllables and, in a second task, move their lips or tongue. Speech perception most strongly activated superior temporal cortex. Crucially, however, distinct motor regions in the precentral gyrus sparked by articulatory movements of the lips and tongue were also differentially activated in a somatotopic manner when subjects listened to the lip- or tongue-related phonemes. This sound-related somatotopic activation in precentral gyrus shows that, during speech perception, specific motor circuits are recruited that reflect phonetic distinctive features of the speech sounds encountered, thus providing direct neuroimaging support for specific links between the phonological mechanisms for speech perception and production.

Adult↗

PubMed2006

Reading cinnamon activates olfactory brain regions.

Some words immediately and automatically remind us of odours, smells and scents, whereas other language items do not evoke such associations. This study investigated, for the first time, the abstract linking of linguistic and odour information using modern neuroimaging techniques (functional MRI). Subjects passively read odour-related words ('garlic', 'cinnamon', 'jasmine') and neutral language items. The odour-related terms elicited activation in the primary olfactory cortex, which include the piriform cortex and the amygdala. Our results suggest the activation of widely distributed cortical cell assemblies in the processing of olfactory words. These distributed neuron populations extend into language areas but also reach some parts of the olfactory system. These distributed neural systems may be the basis of the processing of language elements, their related conceptual and semantic information and the associated sensory information.

Amygdala↗

PubMed2006

Tracking speech comprehension in space and time.

A fundamental challenge for the cognitive neuroscience of language is to capture the spatio-temporal patterns of brain activity that underlie critical functional components of the language comprehension process. We combine here psycholinguistic analysis, whole-head magnetoencephalography (MEG), the Mismatch Negativity (MMN) paradigm, and state-of-the-art source localization techniques (Equivalent Current Dipole and L1 Minimum-Norm Current Estimates) to locate the process of spoken word recognition at a specific moment in space and time. The magnetic MMN to words presented as rare "deviant stimuli" in an oddball paradigm among repetitive "standard" speech stimuli, peaked 100-150 ms after the information in the acoustic input, was sufficient for word recognition. The latency with which words were recognized corresponded to that of an MMN source in the left superior temporal cortex. There was a significant correlation (r = 0.7) of latency measures of word recognition in individual study participants with the latency of the activity peak of the superior temporal source. These results demonstrate a correspondence between the behaviorally determined recognition point for spoken words and the cortical activation in left posterior superior temporal areas. Both the MMN calculated in the classic manner, obtained by subtracting standard from deviant stimulus response recorded in the same experiment, and the identity MMN (iMMN), defined as the difference between the neuromagnetic responses to the same stimulus presented as standard and deviant stimulus, showed the same significant correlation with word recognition processes.

Adult↗

PubMed2005

Clinical, imaging and pathological correlates of a hereditary deficit in verb and action processing.

Selective verb and noun deficits have been observed in a number of neurological conditions and their occurrence has been interpreted as evidence for different neural networks underlying the processing of specific word categories. We describe the first case of a familial occurrence of a selective deficit of verb processing. Father (Individual I) and son (Individual II) developed a movement disorder resembling progressive supranuclear palsy (PSP) and associated with dementia. A second child of Individual II remained symptom-free on consecutive examinations. The dissociation between the processing of nouns and verbs in Individuals I and II was confirmed with different methods, including a longitudinal assessment of naming, comprehension, picture and word association, as well as a lexical decision task. The difference remained stable on follow-up testing despite overall deterioration. It was associated with left-sided frontal hypometabolism on FDG-PET imaging (Individual II) and with ubiquitin-positive inclusions on post-mortem examination (Individual I). The association of a selective verb deficit with a familial movement disorder raises the question whether related genetic factors might influence both movements and their abstract conceptual representations in the form of action verbs. By demonstrating a link between pathology, genetics, imaging and abstract cognitive impairments this study advances our understanding of degenerative brain disease with implications for both neuroscience and clinical practice.

Adult↗

PubMed2005

Category-specific conceptual processing of color and form in left fronto-temporal cortex.

To investigate the cortical basis of color and form concepts, we examined event-related functional magnetic resonance imaging (fMRI) responses to matched words related to abstract color and form information. Silent word reading elicited activity in left temporal and frontal cortex, where category-specific activity differences were also observed. Whereas color words preferentially activated anterior parahippocampal gyrus, form words evoked category-specific activity in fusiform and middle temporal gyrus as well as premotor and dorsolateral prefrontal areas in inferior and middle frontal gyri. These results demonstrate that word meanings and concepts are not processed by a unique cortical area, but by different sets of areas, each of which may contribute differentially to conceptual semantic processing. We hypothesize that the anterior parahippocampal activation to color words indexes computation of the visual feature conjunctions and disjunctions necessary for classifying visual stimuli under a color concept. The predominant premotor and prefrontal activation to form words suggests action-related information processing and may reflect the involvement of neuronal elements responding in an either-or fashion to mirror neurons related to adumbrating shapes.

Adult↗

PubMed2005

Category specificity in the processing of color-related and form-related words: an ERP study.

In this study, we investigated the spatio-temporal patterns of category-specific cortical activation elicited by the visual presentation of words whose meaning relates to a color or to a visual form or shape. We recorded the event-related potentials (ERPs) of ten healthy, right-handed volunteers while they passively read words presented tachistoscopically. As early as 150 ms after stimulus onset, the ERPs revealed significant neurophysiological differences between words and strings of hash marks. Around 200 ms after stimulus onset, we found significant differences in the ERPs elicited by color- and form-related words. We used minimum norm current estimates to investigate the spatial location of these differences. This revealed that, at the 150 ms peak, the activation advantage of words over sequences of hash marks was located in a left posterior area, proximal to what has previously been called the visual word form area. At the 200 ms peak, the advantage of words related to colors over words related to forms seemed to reside in temporal cortical areas, whereas the form-related words elicited greater activation in frontal areas than color-related words. These results provide evidence for early access to detailed category-specific representations of word meaning, with subtle differences in meaning being reflected in the activation of different cortical areas, as early as 200 ms after stimulus presentation. In line with previous studies, these differences can be related to the areas involved in the conceptual processing of sensory (visual) and action-related information.

Adult↗

PubMed2005

Therapy-related reorganization of language in both hemispheres of patients with chronic aphasia.

The brain processes of language recovery after stroke are poorly understood, partly because past research did not allow to differentiate the effects of spontaneous restitution processes from those of learning-related cortical reorganization. Here, we use a new approach offered by recently developed intense neuropsychological therapy methods, which allow for improving language functions within a short time period. Stroke patients with chronic aphasia received intense language therapy for 2 weeks and, over this period, improved their language performance as assessed using clinical tests. Neurophysiological activity elicited by words and pseudowords was measured before and after treatment. Over the therapy interval, early word evoked potentials (latency 250-300 ms) became significantly stronger whereas pseudoword responses did not change. Word-specific changes were documented by analyses of ERP amplitudes and root mean square values, which revealed interactions of the factors Assessment time (before vs. after therapy) and Wordness (word vs. pseudoword). Source localization using Minimum Norm Current Estimates showed that bilateral cortical sources activated by word stimuli contributed to the change, suggesting that neuronal networks distributed over both hemispheres are the substrate of cortical reorganization of language processing in intense aphasia therapy. Word-evoked differences in source strengths were significantly correlated with performance on a clinical language test, demonstrating a link between behavioral and neurophysiological changes. We suggest that the early word-evoked negativity might represent an index of reorganization of language after stroke and thus an aphasia recovery potential.

Adult↗

PubMed2005

Determinants of dominance: is language laterality explained by physical or linguistic features of speech?

The nature of cerebral asymmetry of the language function is still not fully understood. Two main views are that laterality is best explained (1) by left cortical specialization for the processing of spectrally rich and rapidly changing sounds, and (2) by a predisposition of one hemisphere to develop a module for phonemes. We tested both of these views by investigating magnetic brain responses to the same brief acoustic stimulus, placed in contexts where it was perceived either as a noise burst with no resemblance of speech, or as a native language sound being part of a meaningless pseudoword. In further experiments, the same acoustic element was placed in the context of words. We found reliable left hemispheric dominance only when the sound was placed in word context. These results, obtained in a passive odd-ball paradigm, suggest that neither physical properties nor phoneme status of a sound are sufficient for laterality. In order to elicit left lateralized cortical activation in normal right-handed individuals, a rapidly changing spectrally rich sound with phoneme status needs to be placed in the context of frequently encountered larger language elements, such as words. This demonstrates that language laterality is bound to the processing of sounds as units of frequently occurring meaningful items and can thus be linked to the processes of learning and memory trace formation for such items rather than to their physical or phonological properties.

Adult↗

PubMed2005

Brain mechanisms linking language and action.

For a long time the cortical systems for language and actions were believed to be independent modules. However, as these systems are reciprocally connected with each other, information about language and actions might interact in distributed neuronal assemblies. A critical case is that of action words that are semantically related to different parts of the body (for example, 'lick', 'pick' and 'kick'): does the comprehension of these words specifically, rapidly and automatically activate the motor system in a somatotopic manner, and does their comprehension rely on activity in the action system?

Animals↗

PubMed2005

Functional links between motor and language systems.

Transcranial magnetic stimulation (TMS) was applied to motor areas in the left language-dominant hemisphere while right-handed human subjects made lexical decisions on words related to actions. Response times to words referring to leg actions (e.g. kick) were compared with those to words referring to movements involving the arms and hands (e.g. pick). TMS of hand and leg areas influenced the processing of arm and leg words differentially, as documented by a significant interaction of the factors Stimulation site and Word category. Arm area TMS led to faster arm than leg word responses and the reverse effect, faster lexical decisions on leg than arm words, was present when TMS was applied to leg areas. TMS-related differences between word categories were not seen in control conditions, when TMS was applied to hand and leg areas in the right hemisphere and during sham stimulation. Our results show that the left hemispheric cortical systems for language and action are linked to each other in a category-specific manner and that activation in motor and premotor areas can influence the processing of specific kinds of words semantically related to arm or leg actions. By demonstrating specific functional links between action and language systems during lexical processing, these results call into question modular theories of language and motor functions and provide evidence that the two systems interact in the processing of meaningful information about language and action.

Adult↗

PubMed2005

Brain signatures of meaning access in action word recognition.

The brain basis of action words may be neuron ensembles binding language- and action-related information that are dispersed over both language- and action-related cortical areas. This predicts fast spreading of neuronal activity from language areas to specific sensorimotor areas when action words semantically related to different parts of the body are being perceived. To test this, fast neurophysiological imaging was applied to reveal spatiotemporal activity patterns elicited by words with different action-related meaning. Spoken words referring to actions involving the face or leg were presented while subjects engaged in a distraction task and their brain activity was recorded using high-density magnetoencephalography. Shortly after the words could be recognized as unique lexical items, objective source localization using minimum norm current estimates revealed activation in superior temporal (130 msec) and inferior frontocentral areas (142-146 msec). Face-word stimuli activated inferior frontocentral areas more strongly than leg words, whereas the reverse was found at superior central sites (170 msec), thus reflecting the cortical somatotopy of motor actions signified by the words. Significant correlations were found between local source strengths in the frontocentral cortex calculated for all participants and their semantic ratings of the stimulus words, thus further establishing a close relationship between word meaning access and neurophysiology. These results show that meaning access in action word recognition is an early automatic process ref lected by spatiotemporal signatures of word-evoked activity. Word-related distributed neuronal assemblies with specific cortical topographies can explain the observed spatiotemporal dynamics reflecting word meaning access.

Acoustic Stimulation↗

PubMed2004

Somatotopic representation of action words in human motor and premotor cortex.

Since the early days of research into language and the brain, word meaning was assumed to be processed in specific brain regions, which most modern neuroscientists localize to the left temporal lobe. Here we use event-related fMRI to show that action words referring to face, arm, or leg actions (e.g., to lick, pick, or kick), when presented in a passive reading task, differentially activated areas along the motor strip that either were directly adjacent to or overlapped with areas activated by actual movement of the tongue, fingers, or feet. These results demonstrate that the referential meaning of action words has a correlate in the somatotopic activation of motor and premotor cortex. This rules out a unified "meaning center" in the human brain and supports a dynamic view according to which words are processed by distributed neuronal assemblies with cortical topographies that reflect word semantics.

Adult↗

PubMed2004

Distributed neuronal networks for encoding category-specific semantic information: the mismatch negativity to action words.

Mismatch negativity (MMN), an index of experience-dependent memory traces, was used to investigate the processing of action-related words in the human brain. Responses to auditorily presented movement-related English words were recorded in a non-attend odd-ball protocol using a high-density electroencephalographic (EEG) set-up. MMN was calculated using responses to the same words presented as standard and deviant stimuli in different sessions to avoid contamination from phonetic-acoustic differences. The topography of the mismatch negativity to action words revealed an unusual centro-posterior distribution of the responses, suggesting that activity was at least in part generated posterior to usually observed frontal MMNs. Moreover, responses to hand-related word stimulus (pick) had a more widespread lateral distribution, whereas leg-related stimulus (kick) elicited a more focal dorsal negativity. These differences, remarkably reminiscent of sensorimotor cortex topography, were further assessed using distributed source analysis of the EEG signal (L2 minimum-norm current estimates). The source analysis also confirmed differentially distributed activation for the two stimuli. We suggest that these results indicate activation of distributed neuronal assemblies that function as category-specific memory traces for words and may involve sensorimotor cortical structures for encoding action words.

Acoustic Stimulation↗

PubMed2004

Enhanced mismatch negativity brain response after binaural word presentation.

Abstract An oddball paradigm was used to investigate brain processes elicited by spoken words and pseudowords played monaurally, to the left or right ear, or simultaneously to both ears of human subjects instructed to ignore acoustic stimuli but watch a silent video film. The mismatch negativity (MMN), a neurophysiological index of the automatic activation of cortical memory traces, was calculated as the difference between the event-related potential elicited by an infrequent deviant stimulus and the event-related potential to the same item presented as a frequent standard stimulus. Consistent with earlier reports, the MMN to words was larger than that to pseudowords, possibly reflecting the existence of memory traces for spoken words. Bilateral redundant stimulus presentation led to a further increase of the MMN to words relative to both unilateral stimulation modes. This bilateral redundancy gain was absent for pseudowords. We interpret the neurophysiological manifestation of a word-specific bilateral redundancy gain as evidence for interhemispheric cooperation in the automatic access to memory traces for spoken words. Accordingly, word-related cortical networks distributed over both hemispheres allow summation of neural activity between and within hemispheres, thereby potentiating the word-related MMN.

Acoustic Stimulation↗

PubMed2004

Word-specific cortical activity as revealed by the mismatch negativity.

Neurophysiological brain activity evoked by individual spoken words and pseudowords was recorded and the mismatch negativity (MMN), an automatic index of experience-dependent auditory memory traces, was calculated. Consistent with earlier reported results, the MMN response to word-final syllables was enhanced compared with that elicited by the same syllables placed in a pseudoword context. Here we now demonstrate that the enhancement of the MMN elicited by two individual words showed different scalp topographies. The early word-specific brain activity is consistent with the assumption that the memory traces activated by individual words are carried by large neuronal ensembles that differ in their distributions over the cortex. Current source estimates localized the between-word differences in the right hemisphere and in parieto-occipital left-hemispheric areas. The differential brain responses to individual words appeared as early as approximately 100 ms after the recognition points of the words, suggesting that their specific memory traces become active almost immediately after the information in the acoustic input is sufficient for word identification.

Adult↗