Efficient time splitting schemes for the monodomain equation in cardiac electrophysiology.

Approximating the fast dynamics of depolarization waves in the human heart described by the monodomain model is numerically challenging. Splitting methods for the PDE-ODE coupling enable the computation with very fine space and time discretizations. Here, we compare different splitting approaches regarding convergence, accuracy, and efficiency. Simulations were performed for a benchmark problem with the Beeler-Reuter cell model on a truncated ellipsoid approximating the left ventricle including a localized stimulation. For this configuration, we provide a reference solution for the transmembrane potential. We found a semi-implicit approach with state variable interpolation to be the most efficient scheme. The results are transferred to a more physiological setup using a bi-ventricular domain with a complex external stimulation pattern to evaluate the accuracy of the activation time for different resolutions in space and time.

Vitamin A supplements, routine immunization, and the subsequent risk of Plasmodium infection among children under 5 years in sub-Saharan Africa.

Recent studies, partly based on murine models, suggest childhood immunization and vitamin A supplements may confer protection against malaria infection, although strong evidence to support these theories in humans has so far been lacking. We analyzed national survey data from children aged 6-59 months in four sub-Saharan African countries over an 18-month time period, to determine the risk of Plasmodium spp. parasitemia (n=8390) and Plasmodium falciparum HRP-2 (PfHRP-2)-related antigenemia (n=6121) following vitamin A supplementation and standard vaccination. Bacille Calmette Guerin-vaccinated children were more likely to be PfHRP-2 positive (relative risk [RR]=4.06, 95% confidence interval [CI]=2.00-8.28). No association was identified with parasitemia. Measles and polio vaccination were not associated with malaria. Children receiving vitamin A were less likely to present with parasitemia (RR=0.46, 95% CI=0.39-0.54) and antigenemia (RR=0.23, 95% CI=0.17-0.29). Future studies focusing on climate seasonality, placental malaria and HIV are needed to characterize better the association between vitamin A and malaria infection in different settings.

Integrative approach for the treatment of posttraumatic stress disorder in 9/11 first responders: three core techniques.

We describe an integrative psychotherapy for first responders to the September 11, 2001 terrorist attack, including those who continue to be psychologically impacted by these events, most of whom meet criteria for a diagnosis of posttraumatic stress disorder. Three core techniques used in this treatment are described: (a) an emphasis on meaning making, particularly regarding the traumatic event; (b) focus on the most affect-laden components of the traumatic exposure; and (c) identifying and challenging the implicit strategies used by individuals to avoid discussion of components of their traumatic memories and the attendant negative affect. For each intervention, a theoretical rationale and the presumed mechanism of operation are presented. We discuss the clinical and research implications of this intervention.

Learning across senses: cross-modal effects in multisensory statistical learning.

It is currently unknown whether statistical learning is supported by modality-general or modality-specific mechanisms. One issue within this debate concerns the independence of learning in one modality from learning in other modalities. In the present study, the authors examined the extent to which statistical learning across modalities is independent by simultaneously presenting learners with auditory and visual streams. After establishing baseline rates of learning for each stream independently, they systematically varied the amount of audiovisual correspondence across 3 experiments. They found that learners were able to segment both streams successfully only when the boundaries of the audio and visual triplets were in alignment. This pattern of results suggests that learners are able to extract multiple statistical regularities across modalities provided that there is some degree of cross-modal coherence. They discuss the implications of their results in light of recent claims that multisensory statistical learning is guided by modality-independent mechanisms.

Statistical phonetic learning in infants: facilitation and feature generalization.

Over the course of the first year of life, infants develop from being generalized listeners, capable of discriminating both native and non-native speech contrasts, into specialized listeners whose discrimination patterns closely reflect the phonetic system of the native language(s). Recent work by Maye, Werker and Gerken (2002) has proposed a statistical account for this phenomenon, showing that infants may lose the ability to discriminate some foreign language contrasts on the basis of their sensitivity to the statistical distribution of sounds in the input language. In this paper we examine the process of enhancement in infant speech perception, whereby initially difficult phonetic contrasts become better discriminated when they define two categories that serve a functional role in the native language. In particular, we demonstrate that exposure to a bimodal statistical distribution in 8-month-old infants' phonetic input can lead to increased discrimination of difficult contrasts. In addition, this exposure also facilitates discrimination of an unfamiliar contrast sharing the same phonetic feature as the contrast presented during familiarization, suggesting that infants extract acoustic/phonetic information that is invariant across an abstract featural representation.

Temporal instability of auditory and visual event-related potentials in posttraumatic stress disorder.

BACKGROUND: We examined P300 measures in patients with posttraumatic stress disorder (PTSD) and control subjects at two different time points to determine event-related potential (ERP) stability over time and the relationship of changes in ERPs to changes in symptom levels. METHODS: Auditory and visual P300 was recorded in a three-condition novelty oddball task in 25 male subjects with combat-related PTSD and 15 male combat-exposed normal control subjects at two time points separated by 6-12 months. Regression analyses were conducted to compare the temporal stability of ERP measures in PTSD and control subjects. Variability in ERP measures over time within PTSD subjects was examined for association with changes in symptom levels. RESULTS: There were no significant differences in P300 amplitude or latency in PTSD versus control subjects at either time point, regardless of stimulus type (target, novel) or modality (auditory, visual). Nine of 24 P300 measures were significantly less predictable over time in the PTSD group compared to control subjects. Variability of P300 measures over time was not associated with fluctuations in symptoms of depression or PTSD. CONCLUSIONS: P300 ERPs are more variable cross-sectionally and over time in PTSD subjects compared to trauma exposed control subjects. Measures of variability about the group mean appear to be more informative about the cognitive electrophysiology of PTSD than measures of central tendency.