The costs of freedom: an ERP -- study of non-canonical sentences.

OBJECTIVES: The present investigation explored the electrophysiological correlates of working memory during sentence comprehension. METHODS: Event-related brain potentials (ERP) were recorded from 29 channels in 22 subjects, while they read German sentences having subject-first (canonical) or object-first (non-canonical) word orders. RESULTS: Three different ERP effects were observed: a negativity (maximum at Fc5) differentiating unambiguous object-first and subject-first sentences, interpreted as reflecting the demands of the object-first sentences on working memory; a second negativity (maximum at F7) to the subject noun-phrase in object-first sentences, interpreted as indicating retrieval of verbal material. Finally, a parietal positivity was found for ambiguous sentences that turned out to have a non-canonical word order, which was interpreted as indicating revision and reevaluation processes. CONCLUSIONS: The present data underscore the different roles of working memory in comprehension.

Incidental and intentional learning of verbal episodic material differentially modifies functional brain networks.

Learning- and memory-related processes are thought to result from dynamic interactions in large-scale brain networks that include lateral and mesial structures of the temporal lobes. We investigate the impact of incidental and intentional learning of verbal episodic material on functional brain networks that we derive from scalp-EEG recorded continuously from 33 subjects during a neuropsychological test schedule. Analyzing the networks' global statistical properties we observe that intentional but not incidental learning leads to a significantly increased clustering coefficient, and the average shortest path length remains unaffected. Moreover, network modifications correlate with subsequent recall performance: the more pronounced the modifications of the clustering coefficient, the higher the recall performance. Our findings provide novel insights into the relationship between topological aspects of functional brain networks and higher cognitive functions.

State dependent properties of epileptic brain networks: comparative graph-theoretical analyses of simultaneously recorded EEG and MEG.

OBJECTIVE: To investigate whether functional brain networks of epilepsy patients treated with antiepileptic medication differ from networks of healthy controls even during the seizure-free interval. METHODS: We applied different rules to construct binary and weighted networks from EEG and MEG data recorded under a resting-state eyes-open and eyes-closed condition from 21 epilepsy patients and 23 healthy controls. The average shortest path length and the clustering coefficient served as global statistical network characteristics. RESULTS: Independent on the behavioral condition, epileptic brains exhibited a more regular functional network structure. Similarly, the eyes-closed condition was characterized by a more regular functional network structure in both groups. The amount of network reorganization due to behavioral state changes was similar in both groups. Consistent findings could be achieved for networks derived from EEG but hardly from MEG recordings, and network construction rules had a rather strong impact on our findings. CONCLUSIONS: Despite the locality of the investigated processes epileptic brain networks differ in their global characteristics from non-epileptic brain networks. Further methodological developments are necessary to improve the characterization of disturbed and normal functional networks. SIGNIFICANCE: An increased regularity and a diminished modulation capability appear characteristic of epileptic brain networks.

Both sides get the point: hemispheric sensitivities to sentential constraint.

Behavioral studies have consistently reported striking differences in the impact of sentence-level information on the processing of words presented in the right (RVF) versus the left (LVF) visual field, with context effects apparent only for RVF items. The consistent lack of such effects in the LVF has been taken to mean that right hemisphere language comprehension is largely insensitive to message-level meaning. We used the functional specificity afforded by event-related potential measures to assess this claim. Target words completing strongly and weakly constraining sentence contexts, in which constraint arose at the sentence level rather than from lexical associations, were presented laterally in the LVF or RVF. Increased constraint significantly reduced N400 amplitudes with presentation in both VFs, with no differences in the timing or amplitude of these effects. These results are inconsistent with the view that the VF asymmetries found in behavioral measures reflect differential hemispheric capacities at the level of semantic analysis and integration, although VF-based differences on earlier components (P2) suggest asymmetries in the impact of sentential context on perceptual aspects of word processing in the two hemispheres.