The N400 and Late Positive Complex (LPC) Effects Reflect Controlled Rather than Automatic Mechanisms of Sentence Processing.

This study compared automatic and controlled cognitive processes that underlie event-related potentials (ERPs) effects during speech perception. Sentences were presented to French native speakers, and the final word could be congruent or incongruent, and presented at one of four levels of degradation (using a modulation with pink noise): no degradation, mild degradation (2 levels), or strong degradation. We assumed that degradation impairs controlled more than automatic processes. The N400 and Late Positive Complex (LPC) effects were defined as the differences between the corresponding wave amplitudes to incongruent words minus congruent words. Under mild degradation, where controlled sentence-level processing could still occur (as indicated by behavioral data), both N400 and LPC effects were delayed and the latter effect was reduced. Under strong degradation, where sentence processing was rather automatic (as indicated by behavioral data), no ERP effect remained. These results suggest that ERP effects elicited in complex contexts, such as sentences, reflect controlled rather than automatic mechanisms of speech processing. These results differ from the results of experiments that used word-pair or word-list paradigms.

Emotional electrodermal response in coma and other low-responsive patients.

Emotional processing in coma remains an open question. Skin conductance responses to emotional and neutral auditory stimuli were recorded in 13 low-responsive patients (12 of whom were in coma). A differential response between emotional and neutral stimuli was found, which significantly correlated with the Glasgow Coma Scale and the Cook and Palma score. These correlations indicate that emotional processing can occur in coma patients with relatively high clinical scores of reactivity.

Cortical information processing in coma.

OBJECTIVES: To evaluate cortical information processing (particularly, semantic processing) in acute nontraumatic coma by means of event-related brain potentials (ERPs). METHODS: The tests included measures of obligatory auditory processing (N100), automatic (Mismatch Negativity) and controlled (P300) detection of stimulus deviance, and semantic processing (ERP effects in word pairs and sentences). The tests were presented to 20 healthy participants and 42 coma patients with Glasgow Coma Scale <9. RESULTS: Responders (ie, patients whose ERP data indicate that their brain was able to process the corresponding stimuli) were found in each ERP test, and their distribution was statistically different from that expected by chance. Particularly, 7 responders were found in the word pair paradigm and 3 responders in the sentence paradigm. The P300 responsiveness highly correlated with other ERP responses, with Glasgow Coma Scale and with the future development of coma (ie, P300 on day 4 was related to the clinical state on day 20). CONCLUSIONS: Results suggest a wide range of cortical information processing in coma, including semantic processing. The question is discussed of whether, and to what extent, these processing operations are related to conscious awareness of stimuli.

Sex differences in two event-related potentials components related to semantic priming.

Although sex differences in language processing are well documented in behavioral studies, only a few electrophysiological studies have explored this topic. We analyzed sex differences in two language-related components of event-related potentials (ERPs): the N400 and the Late Positive Complex (LPC). Ten men and 10 women, matched by age and handedness, participated in the study. Two semantic priming paradigms were presented: word pairs (60 congruent and 60 incongruent) and sentences (50 with congruent and 50 with incongruent ending words). In addition, the effect of context was investigated by a comparison between ERP effects obtained in single word priming and sentential priming. The N400 effect was earlier and larger in women, and the LPC effect was larger in men. Furthermore, the LPC effect in men, but not in women, was much larger with sentence priming than with word priming, suggesting that the LPC effect may be more dependent on context in men than in women. The opposite sex difference on the two ERP components indicates different underlying mechanisms. While the LPC effect is thought to be generated by purely explicit mechanisms, such as postlexical integrative processes, the N400 effect may be also governed by prelexical implicit and explicit mechanisms. Our results were consistent with the notion of more automated processing of language in women than in men.

Landau-Kleffner syndrome is not an eponymic badge of ignorance.

In a 1992 editorial article, Landau expressed the hope of collective agreement in the medical community about Landau-Kleffner syndrome (LKS) in terms of diagnosis criteria, etiology, pathophysiology and rational therapy. Since then, neurophysiological and neuroimaging studies have led to the view that LKS is an acquired aphasia, secondary to an epileptic disturbance affecting a cortical area involved in verbal processing. This fits with the hypothesis of a "functional ablation" caused by epileptic activity. Under these criteria, epileptic aphasia becomes a subgroup of the continuous spike-waves syndrome in which epileptic discharges originate from the temporal cortex. Genetic predisposition for KLS could be related to hyperexcitability and synchronization of interneurons within the perisylvian cortices, which generate the spike-waves. Activation of these waves during NREM sleep, following thalamo-cortical uncoupling, might then alter the blood brain barrier and provoke an autoimmune reaction. Interneuron hyperactivity might in turn have an antiepileptic protective effect, associated with the inhibition of a specific function, and spike-waves activity over the long term might eventuate in focal atrophy. This morphological defect might explain the poor verbal outcome in some cases of LKS. From this study we recommend a multicenter control study of good design and methodology be carried out to compare the efficacies of early versus delayed (3 months) corticosteroid treatment in patients with typical LKS that is being treated by clobazam (or diazepam) monotherapy.