Dynamic causal modeling of subcortical connectivity of language.

Subcortical-cortical interactions in the language network were investigated using dynamic causal modeling of magnetoencephalographic data recorded during auditory comprehension. Participants heard sentences that either were correct or contained violations. Sentences containing violations had syntactic or prosodic violations or both. We show that a hidden source, modeling magnetically silent deep nuclei, is required to explain the data best. This is in line with recent brain imaging studies and intracranial recordings suggesting an involvement of subcortical structures in language processing. Here, the processing of syntactic and prosodic violations elicited a global increase in the amplitude of evoked responses, both at the cortical and subcortical levels. As estimated by Bayesian model averaging, this was accompanied by various changes in cortical-cortical and subcortical-cortical connectivity. The most consistent findings in relation to violations were a decrease of reentrant inputs to Heschl's gyrus (HG) and of transcallosal lateral connections. These results suggest that in conditions where one hemisphere detects a violation, possibly via fast thalamocortical (HG) loops, the intercallosal connectivity is reduced to allow independent processing of syntax (left hemisphere) and of prosody (right hemisphere). This study is the first demonstration in cognitive neuroscience that subcortical-cortical loops can be empirically investigated using noninvasive electrophysiological recordings.

Prosody meets syntax: the role of the corpus callosum.

Contemporary neural models of auditory language comprehension proposed that the two hemispheres are differently specialized in the processing of segmental and suprasegmental features of language. While segmental processing of syntactic and lexical semantic information is predominantly assigned to the left hemisphere, the right hemisphere is thought to have a primacy for the processing of suprasegmental prosodic information such as accentuation and boundary marking. A dynamic interplay between the hemispheres is assumed to allow for the timely coordination of both information types. The present event-related potential study investigated whether the anterior and/or posterior portion of the corpus callosum provide the crucial brain basis for the online interaction of syntactic and prosodic information. Patients with lesions in the anterior two-thirds of the corpus callosum connecting orbital and frontal structures, or the posterior third of the corpus callosum connecting temporal, parietal and occipital areas, as well as matched healthy controls, were tested in a paradigm that crossed syntactic and prosodic manipulations. An anterior negativity elicited by a mismatch between syntactically predicted phrase structure and prosodic intonation was analysed as a marker for syntax-prosody interaction. Healthy controls and patients with lesions in the anterior corpus callosum showed this anterior negativity demonstrating an intact interplay between syntax and prosody. No such effect was found in patients with lesions in the posterior corpus callosum, although they exhibited intact, prosody-independent syntactic processing comparable with healthy controls and patients with lesions in the anterior corpus callosum. These data support the interplay between the speech processing streams in the left and right hemispheres via the posterior portion of the corpus callosum, building the brain basis for the coordination and integration of local syntactic and prosodic features during auditory speech comprehension.

It's early: event-related potential evidence for initial interaction of syntax and prosody in speech comprehension.

Psycholinguistic theories assume an interaction between prosody and syntax during language processing. Based on studies using mostly off-line methods, it is unclear whether an interaction occurs at later or initial processing stages. Using event-related potentials, the present study provides neurophysiological evidence for a prosody and syntax interaction in initial processing. The sentence material contained mere prosodic and syntactic as well as combined prosodic-syntactic violations. For the syntax violation, the critical word appeared after a preposition. The suffix of the critical word either indicated a noun fulfilling the syntactic requirements of the preceding preposition or a verb causing a word category violation. For the prosodic manipulation, congruent critical words were normally intonated (signaling sentence continuation) while prosodically incongruent critical words signaled sentence end. For the mere prosodic incongruity, a broadly distributed negativity was observed at the critical word-stem (300-500 msec aligned to word onset). In response to a mere syntactic error, a left temporal negativity was elicited in an early time window (200-400 msec aligned to suffix onset), taken to reflect initial phrase structure building processes. In contrast, in response to the combined prosodic-syntactic violation, an early temporal negativity showed up bilaterally at the suffix in the same time window. Our interpretation is that the process of initial structure building as reflected in the early left anterior negativity recruits additional right hemispheric neural resources when the critical word contains both syntactic and prosodic violations. This suggests the immediate influence of phrasal prosody during the initial parsing stage in speech processing.

Late interaction of syntactic and prosodic processes in sentence comprehension as revealed by ERPs.

The present study was designed to examine the processing of prosodic and syntactic information in spoken language. The aim was to investigate the long discussed relationship between prosody and syntax in online speech comprehension to reveal direct evidence about whether the two information types are interactive or independent from each other. The method of event-related potentials allowed us to sheet light on the precise time course of this relationship. Our experimental manipulation involved two prosodically different positions in German sentences, i.e., the critical noun in penultimate vs. final position. In syntactically correct sentences, a prosodic manipulation of the penultimate word gave rise to a late centroparietal negativity that resembled the classical N400 component. We interpreted the negativity as a correlate of lexical integration costs for the prosodically unexpected sentence-final word. Comparisons with syntactically incorrect sentences revealed that this effect was dependent on the sentences' grammatical correctness. When the prosodic manipulation was realized at the final word, we observed a right anterior negativity followed by a late positivity (P600). The right anterior negativity was present independent of the sentences' grammatical correctness. However, the P600 was not, as a late positivity was present for straightforward prosodic and syntactic violations but increased for the combined violations. This suggests that the right anterior negativity, and not the P600, should be considered as a pure prosodic effect. The combined data moreover suggest an interaction between prosody and syntax in a later time window during sentence comprehension.

Brain signatures of syntactic and semantic processes during children's language development.

Developmental aspects of language comprehension were investigated using event-related brain potentials. Children between the ages of 6 and 13 listened to passive sentences that were correct, semantically incorrect, or syntactically incorrect, and data in each condition were compared with those of adults. For semantic violations, adults demonstrated a negativity (N400), as did children, but the latency decreased with age. For syntactic violations, adults displayed an early left anterior negativity (ELAN) and a late centro-parietal positivity (P600). A syntactic negativity and a late positivity were also present for children between 7 and 13 years, again with latency decreasing with age. Six-year-olds, in contrast, did not demonstrate an ELAN effect, but a late, reduced P600 pattern for the syntactic violation condition. In the early time window, the 6-year-olds displayed a widely distributed negativity that was larger for the correct than for the syntactically incorrect condition. These data indicate that the neurophysiological basis for semantic processes during auditory sentence comprehension does not change dramatically between early childhood and adulthood. Syntactic processes for passive sentences appear to differ between early and late childhood, at least with respect to those processes reflected in the ELAN component. As there is evidence that the ELAN reflects highly automatic structure-building processes, we conclude that these processes are not yet established at age 7, but gradually develop toward adult-like processing during late childhood.