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

Rebound Discharge in Deep Cerebellar Nuclear Neurons In Vitro

Neurons of the deep cerebellar nuclei (DCN) play a critical role in defining the output of cerebellum in the course of encoding Purkinje cell inhibitory inputs. The earliest work performed with in vitro preparations established that DCN cells have the capacity to translate membrane hyperpolarizations into a rebound increase in firing frequency. The primary means of distinguishing between DCN neurons has been according to cell size and transmitter phenotype, but in some cases, differences in the firing properties of DCN cells maintained in vitro have been reported. In particular, it was shown that large diameter cells in the rat DCN exhibit two phenotypes of rebound discharge in vitro that may eventually help define their functional roles in cerebellar output. A transient burst and weak burst phenotype can be distinguished based on the frequency and pattern of rebound discharge immediately following a hyperpolarizing stimulus. Work to date indicates that the difference in excitability arises from at least the degree of activation of T-type Ca2+ current during the immediate phase of rebound firing and Ca2+-dependent K+ channels that underlie afterhyperpolarizations. Both phenotypes can be detected following stimulation of Purkinje cell inhibitory inputs under conditions that preserve resting membrane potential and natural ionic gradients. In this paper, we review the evidence supporting the existence of different rebound phenotypes in DCN cells and the ion channel expression patterns that underlie their generation

On the pathway to better birth outcomes? A systematic review of azithromycin and curable sexually transmitted infections.

The WHO recommends the administration of sulfadoxine-pyrimethamine (SP) to all pregnant women living in areas of moderate (stable) to high malaria transmission during scheduled antenatal visits, beginning in the second trimester and continuing to delivery. Malaria parasites have lost sensitivity to SP in many endemic areas, prompting the investigation of alternatives that include azithromycin-based combination (ABC) therapies. Use of ABC therapies may also confer protection against curable sexually transmitted infections and reproductive tract infections (STIs/RTIs). The magnitude of protection at the population level would depend on the efficacy of the azithromycin-based regimen used and the underlying prevalence of curable STIs/RTIs among pregnant women who receive preventive treatment. This systematic review summarizes the efficacy data of azithromycin against curable STIs/RTIs

Vocal learning promotes patterned inhibitory connectivity

Complex motor behaviors such as birdsong are learned through practice and are thought to depend on specific excitatory connectivity in premotor circuits. Here the authors show that song learning in Bengalese Finches is associated with enrichment of inhibitory network connectivity that can affect specific song features

Psychosocial variables associated with colorectal cancer screening in South Australia

Background: Population screening reduces mortality from colorectal cancer, yet factors associated with uptake of screening are incompletely understood. Purpose: The purpose of the study was to determine demographic and psychosocial factors associated with participation in faecal occult blood test (FOBT)-based colorectal cancer (CRC) screening in an average risk community programme in Adelaide, South Australia. Method: A questionnaire consistent with the Preventive Health Model was used to determine demographic and psychosocial differences between previous FOBT-based screening participants (n = 413, response rate 93.2%) and non-participants (n = 481, response rate 47.9%). Results were analysed by univariate and multivariate generalised linear modelling, and factors associated with participation were identified. Results: Factor analysis of psychosocial items revealed an optimal three-factor solution (knowledge, faecal aversion, belief in the value of screening). Following multivariate analyses, two psychosocial and two demographic factors remained as predictors of FOBT screening behaviour: (1) items related to faecal aversion (Aversion), relative risk (RR) = 0.61, CI = 0.55–0.69, (2) perceptions about the value of screening (Value), RR = 1.45, CI = 1.13–1.85, (3) age band 65–69 (Age, five age bands, relative to age 50–54), RR = 1.43, CI = 1.16–1.76 and FOBT type (Test; three tests, Hemoccult®, FlexSure®, InSure® randomly assigned, relative to Hemoccult®: FlexSure®: RR = 1.41, CI = 1.17–1.71, InSure®: RR = 1.76, CI = 1.47–2.11. Conclusions: The psychosocial factors associated with non-participation in FOBT-based CRC screening are amenable to interventions designed to improve participation. The small relative risks values associated with each predictor, however, raise the possibility that additional factors are likely to influence screening participation.Stephen R. Cole, Ian Zajac, Tess Gregory, Sarah Mehaffey, Naomi Roosa, Deborah Turnbull, Adrian Esterman, Graeme P. Youn