The representation of the verb's argument structure as disclosed by fMRI.

BACKGROUND: In the composition of an event the verb's argument structure defines the number of participants and their relationships. Previous studies indicated distinct brain responses depending on how many obligatory arguments a verb takes. The present functional magnetic resonance imaging (fMRI) study served to verify the neural structures involved in the processing of German verbs with one (e.g. "snore") or three (e.g. "gives") argument structure. Within a silent reading design, verbs were presented either in isolation or with a minimal syntactic context ("snore" vs. "Peter snores"). RESULTS: Reading of isolated one-argument verbs ("snore") produced stronger BOLD responses than three-argument verbs ("gives") in the inferior temporal fusiform gyrus (BA 37) of the left hemisphere, validating previous magnetoencephalographic findings. When presented in context one-argument verbs ("Peter snores") induced more pronounced activity in the inferior frontal gyrus (IFG) of the left hemisphere than three-argument verbs ("Peter gives"). CONCLUSION: In line with previous studies our results corroborate the left temporal lobe as site of representation and the IFG as site of processing of verbs' argument structure.

Distinct processing of function verb categories in the human brain.

A subset of German function verbs can be used either in a full, concrete, 'heavy' ("take a computer") or in a more metaphorical, abstract or 'light' meaning ("take a shower", no actual 'taking' involved). The present magnetoencephalographic (MEG) study explored whether this subset of 'light' verbs is represented in distinct cortical processes. A random sequence of German 'heavy', 'light', and pseudo verbs was visually presented in three runs to 22 native German speakers, who performed lexical decision task on real versus pseudo verbs. Across runs, verbs were presented (a) in isolation, (b) in minimal context of a personal pronoun, and (c) 'light' verbs only in a disambiguating context sentence. Central posterior activity 95-135 ms after stimulus onset was more pronounced for 'heavy' than for 'light' uses, whether presented in isolation or in minimal context. Minimal context produced a similar heavy>light differentiation in the left visual word form area at 160-200 ms. 'Light' verbs presented in sentence context allowing only for a 'heavy reading' evoked larger left-temporal activation around 270-340 ms than the corresponding 'light reading'. Across runs, real verbs provoked more pronounced activation than pseudo verbs in left-occipital regions at 110-150 ms. Thus, 'heavy' versus 'light readings' of verbs already modulate early posterior visual evoked response even when verbs are presented in isolation. This response becomes clearer in the disambiguating contextual condition. This type of study shows for the first time that language processing is sensitive to representational differences between two readings of one and the same verb stem.

Representation of the verb's argument-structure in the human brain.

BACKGROUND: A verb's argument structure defines the number and relationships of participants needed for a complete event. One-argument (intransitive) verbs require only a subject to make a complete sentence, while two- and three-argument verbs (transitives and ditransitives) normally take direct and indirect objects. Cortical responses to verbs embedded into sentences (correct or with syntactic violations) indicate the processing of the verb's argument structure in the human brain. The two experiments of the present study examined whether and how this processing is reflected in distinct spatio-temporal cortical response patterns to isolated verbs and/or verbs presented in minimal context. RESULTS: The magnetoencephalogram was recorded while 22 native German-speaking adults saw 130 German verbs, presented one at a time for 150 ms each in experiment 1. Verb-evoked electromagnetic responses at 250 - 300 ms after stimulus onset, analyzed in source space, were higher in the left middle temporal gyrus for verbs that take only one argument, relative to two- and three-argument verbs. In experiment 2, the same verbs (presented in different order) were preceded by a proper name specifying the subject of the verb. This produced additional activation between 350 and 450 ms in or near the left inferior frontal gyrus, activity being larger and peaking earlier for one-argument verbs that required no further arguments to form a complete sentence. CONCLUSION: Localization of sources of activity suggests that the activation in temporal and frontal regions varies with the degree by which representations of an event as a part of the verbs' semantics are completed during parsing.

Grammar or serial order?: discrete combinatorial brain mechanisms reflected by the syntactic mismatch negativity.

If word strings violate grammatical rules, they elicit neurophysiological brain responses commonly attributed to a specifically human language processor or grammar module. However, an ungrammatical string of words is always also a very rare sequence of events and it is, therefore, not always evident whether specifically linguistic processes are at work when neurophysiological grammar indexes are being reported. We here investigate the magnetic mismatch negativity (MNN) to ungrammatical word strings, to very rare grammatical strings, and to common grammatical phrases. In this design, serial order mechanism mapping the sequential probability of words should neurophysiologically dissociate frequent grammatical phrases from both ungrammatical and rare grammatical strings. However, if syntax as a discrete combinatorial system is reflected, the prediction is that the rare, correctly combined items group with the highly frequent grammatical strings and stand out against ungrammatical strings. Using magnetoencephalography as a measure of human brain activity, we replicated the previously reported syntactic mismatch negativity (sMMN), which distinguishes highly unfamiliar ungrammatical word sequences from common grammatical strings. Crucially, a significant interaction demonstrated that the sMMN specifically distinguished syntactic violations from common grammatical strings, but not uncommon from common grammatical word strings. This significant interaction argues in favor of a genuinely grammatical origin of the sMMN and provides direct neurophysiological evidence for a discrete combinatorial system for word and morpheme sequences in the human brain. The data are more difficult to explain in the context of serial order models that map co-occurrence probabilities of words.

Emotional and semantic networks in visual word processing: insights from ERP studies.

The event-related brain potential (ERP) literature concerning the impact of emotional content on visual word processing is reviewed and related to general knowledge on semantics in word processing: emotional connotation can enhance cortical responses at all stages of visual word processing following the assembly of visual word form (up to 200 ms), such as semantic access (around 200 ms), allocation of attentional resources (around 300 ms), contextual analysis (around 400 ms), and sustained processing and memory encoding (around 500 ms). Even earlier effects have occasionally been reported with subliminal or perceptual threshold presentation, particularly in clinical populations. Here, the underlying mechanisms are likely to diverge from the ones operational in standard natural reading. The variability in timing of the effects can be accounted for by dynamically changing lexical representations that can be activated as required by the subjects' motivational state, the task at hand, and additional contextual factors. Throughout, subcortical structures such as the amygdala are likely to contribute these enhancements. Further research will establish whether or when emotional arousal, valence, or additional emotional properties drive the observed effects and how experimental factors interact with these. Meticulous control of other word properties known to affect ERPs in visual word processing, such as word class, length, frequency, and concreteness and the use of more standardized EEG procedures is vital. Mapping the interplay between cortical and subcortical mechanisms that give rise to amplified cortical responses to emotional words will be of highest priority for future research.

Brain regions essential for improved lexical access in an aged aphasic patient: a case report.

BACKGROUND: The relationship between functional recovery after brain injury and concomitant neuroplastic changes is emphasized in recent research. In the present study we aimed to delineate brain regions essential for language performance in aphasia using functional magnetic resonance imaging and acquisition in a temporal sparse sampling procedure, which allows monitoring of overt verbal responses during scanning. CASE PRESENTATION: An 80-year old patient with chronic aphasia (2 years post-onset) was investigated before and after intensive language training using an overt picture naming task. Differential brain activation in the right inferior frontal gyrus for correct word retrieval and errors was found. Improved language performance following therapy was mirrored by increased fronto-thalamic activation while stability in more general measures of attention/concentration and working memory was assured. Three healthy age-matched control subjects did not show behavioral changes or increased activation when tested repeatedly within the same 2-week time interval. CONCLUSION: The results bear significance in that the changes in brain activation reported can unequivocally be attributed to the short-term training program and a language domain-specific plasticity process. Moreover, it further challenges the claim of a limited recovery potential in chronic aphasia, even at very old age. Delineation of brain regions essential for performance on a single case basis might have major implications for treatment using transcranial magnetic stimulation.

Neuromagnetic brain responses to words from semantic sub- and supercategories.

BACKGROUND: We explored spatio-temporal patterns of cortical activity evoked by written words from super-ordinate and sub-ordinate semantic categories and hoped to find a differential cortical and/or temporal distribution of the brain response depending on the level of the categories. Twenty-three subjects saw 360 words belonging to six sub-ordinate categories (mammals, birds, fish, fruit, flowers, trees) within two super-ordinate categories (fauna, flora). Visually evoked magnetic fields were determined from whole-head (148-sensor) magnetoencephalography and analyzed in the source space (Minimum Norm Estimate). RESULTS: Activity (MNE amplitudes) 100-150 ms after stimulus onset in the left occipito-temporal area distinguished super-ordinate categories, while later activity (300-550 ms) in the left temporal area distinguished the six sub-ordinate categories. CONCLUSION: Our results document temporally and spatially distinct processing and representation of words according to their categorical information. If further studies can rule out possible confounds then our results may help constructing a theory about the internal structure of entries in the mental lexicon and its access.

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).