Characterization of K-Complexes and Slow Wave Activity in a Neural Mass Model

NREM sleep is characterized by two hallmarks, namely K-complexes (KCs) during sleep stage N2 and cortical slow oscillations (SOs) during sleep stage N3. While the underlying dynamics on the neuronal level is well known and can be easily measured, the resulting behavior on the macroscopic population level remains unclear. On the basis of an extended neural mass model of the cortex, we suggest a new interpretation of the mechanisms responsible for the generation of KCs and SOs. As the cortex transitions from wake to deep sleep, in our model it approaches an oscillatory regime via a Hopf bifurcation. Importantly, there is a canard phenomenon arising from a homoclinic bifurcation, whose orbit determines the shape of large amplitude SOs. A KC corresponds to a single excursion along the homoclinic orbit, while SOs are noise-driven oscillations around a stable focus. The model generates both time series and spectra that strikingly resemble real electroencephalogram data and points out possible differences between the different stages of natural sleep

A Thalamocortical Neural Mass Model of the EEG during NREM Sleep and Its Response to Auditory Stimulation

Few models exist that accurately reproduce the complex rhythms of the thalamocortical system that are apparent in measured scalp EEG and at the same time, are suitable for large-scale simulations of brain activity. Here, we present a neural mass model of the thalamocortical system during natural non-REM sleep, which is able to generate fast sleep spindles (12–15 Hz), slow oscillations (<1 Hz) and K-complexes, as well as their distinct temporal relations, and response to auditory stimuli. We show that with the inclusion of detailed calcium currents, the thalamic neural mass model is able to generate different firing modes, and validate the model with EEG-data from a recent sleep study in humans, where closed-loop auditory stimulation was applied. The model output relates directly to the EEG, which makes it a useful basis to develop new stimulation protocols

Use of procalcitonin as a biomarker for sepsis in moderate to major paediatric burns

Introduction: Accurate and early detection of sepsis poses a significant challenge in burn populations. Our objective was to assess whether procalcitonin is a marker of blood culture positive sepsis in moderate to severe paediatric burns. Methods: We analysed procalcitonin levels in 27 children admitted with burns of 15–65% total body surface area. Procalcitonin was measured at admission (baseline), 24 and 48 h post-admission and during periods of suspected sepsis (diagnosed against pre-defined criteria). Patients were categorised into controls with no episodes of suspected sepsis (n = 10) and those with episodes of suspected sepsis (n = 17). The latter were split into two groups based on blood culture results: culture positive (bacteraemia) and culture negative patients. Results: Baseline procalcitonin levels increased with burn size (odds ratio (95% confidence interval): 1.15 (1.02–1.29)). Suspected sepsis patients had larger burns than controls (median 31 vs. 20%; p = 0.003). Only 5/23 suspected sepsis episodes were blood culture positive. Procalcitonin levels were similar in culture positive and culture negative patients (p = 0.43). Sensitivity for predicting positive blood culture was 100% (95% confidence interval: 47.8–100.0%) but specificity was only 22.2% (95% confidence interval: 6.4–47.6%). Area under the curve was poor at 0.62 (95% confidence interval: 0.33–0.90). There was no significant change in procalcitonin levels from baseline to septic episode in either group (positive: p = 0.35; negative: p = 0.95). Conclusion: We conclude that evidence for the use of procalcitonin to diagnose bacteraemia in this population is poor, with burn size playing a significant role implying a correlation with systemic inflammation rather than sepsis

Intracontinental spread of human invasive Salmonella Typhimurium pathovariants in sub-Saharan Africa

A highly invasive form of non-typhoidal Salmonella (iNTS) disease has recently been documented in many countries in sub-Saharan Africa. The most common Salmonella enterica serovar causing this disease is Typhimurium (Salmonella Typhimurium). We applied whole-genome sequence–based phylogenetic methods to define the population structure of sub-Saharan African invasive Salmonella Typhimurium isolates and compared these to global Salmonella Typhimurium populations. Notably, the vast majority of sub-Saharan invasive Salmonella Typhimurium isolates fell within two closely related, highly clustered phylogenetic lineages that we estimate emerged independently ~52 and ~35 years ago in close temporal association with the current HIV pandemic. Clonal replacement of isolates from lineage I by those from lineage II was potentially influenced by the use of chloramphenicol for the treatment of iNTS disease. Our analysis suggests that iNTS disease is in part an epidemic in sub-Saharan Africa caused by highly related Salmonella Typhimurium lineages that may have occupied new niches associated with a compromised human population and antibiotic treatment