A spatially extended model for macroscopic spike-wave discharges

Spike-wave discharges are a distinctive feature of epileptic seizures. So far, they have not been reported in spatially extended neural field models. We study a space-independent version of the Amari neural field model with two competing inhibitory populations. We show that this competition leads to robust spike-wave dynamics if the inhibitory populations operate on different time-scales. The spike-wave oscillations present a fold/homoclinic type bursting. From this result we predict parameters of the extended Amari system where spike-wave oscillations produce a spatially homogeneous pattern. We propose this mechanism as a prototype of macroscopic epileptic spike-wave discharges. To our knowledge this is the first example of robust spike-wave patterns in a spatially extended neural field model.     

Transitions to spike-wave oscillations and epileptic dynamics in a human cortico-thalamic mean-field model

In this paper we present a detailed theoretical analysis of the onset of spike-wave activity in a model of human electroencephalogram (EEG) activity, relating this to clinical recordings from patients with absence seizures. We present a complete explanation of the transition from inter-ictal activity to spike and wave using a combination of bifurcation theory, numerical continuation and techniques for detecting the occurrence of inflection points in systems of delay differential equations (DDEs). We demonstrate that the initial transition to oscillatory behaviour occurs as a result of a Hopf bifurcation, whereas the addition of spikes arises as a result of an inflection point of the vector field. Strikingly these findings are consistent with EEG data recorded from patients with absence seizures and we present a discussion of the clinical significance of these results, suggesting potential new techniques for detection and anticipation of seizures.     

Towards a large-scale model of patient-specific epileptic spike-wave discharges

Clinical electroencephalographic (EEG) recordings of the transition into generalised epileptic seizures show a sudden onset of spike-wave dynamics from a low-amplitude irregular background. In addition, non-trivial and variable spatio-temporal dynamics are widely reported in combined EEG/fMRI studies on the scale of the whole cortex. It is unknown whether these characteristics can be accounted for in a large-scale mathematical model with fixed heterogeneous long-range connectivities. Here, we develop a modelling framework with which to investigate such EEG features. We show that a neural field model composed of a few coupled compartments can serve as a low-dimensional prototype for the transition between irregular background dynamics and spike-wave activity. This prototype then serves as a node in a large-scale network with long-range connectivities derived from human diffusion-tensor imaging data. We examine multivariate properties in 42 clinical EEG seizure recordings from 10 patients diagnosed with typical absence epilepsy and 50 simulated seizures from the large-scale model using 10 DTI connectivity sets from humans. The model can reproduce the clinical feature of stereotypy where seizures are more similar within a patient than between patients, essentially creating a patient-specific fingerprint. We propose the approach as a feasible technique for the investigation of patient-specific large-scale epileptic features in space and time.     

The influence of strain and housing on two types of spike-wave discharges in rats

WAG/Rij rats, a genetic model of absence epilepsy, show two types of spike-wave discharges (Type 1 and Type 2) in their EEG activity. The large interindividual variation in the expression of the phenotypes (number and mean duration of spike-wave discharges) suggests that as well as genetic, environmental factors also play a role. The aim of our study was to establish effects of strain and housing on the incidence and expression of both types of paroxysms. Therefore, WAG/Rij and ACI rats were housed from weaning in either an enriched or impoverished environment for 60 days. At three months of age the EEG of the rats was recorded for four hours to examine the effects of strain and housing on the incidence and expression of the two types of paroxysms. Generally, enriched housing led to worsening of Type 1 and Type 2 spike-wave discharges (SWD). However, the number of affected rats and the expression (number and mean duration) of Type 1 and Type 2 spike-wave discharges were differently influenced by strain and housing. This suggests that Type 1 and Type 2 spike-wave discharges are independent phenomena and that number and mean duration of these paroxysms are controlled by different mechanisms. Finally, the worsening of absence seizures after enrichment is different from what has been found for convulsive seizures.     

Stimulus-induced transitions between spike-wave discharges and spindles with the modulation of thalamic reticular nucleus

It is believed that thalamic reticular nucleus (TRN) controls spindles and spike-wave discharges (SWD) in seizure or sleeping processes. The dynamical mechanisms of spatiotemporal evolutions between these two types of activity, however, are not well understood. In light of this, we first use a single-compartment thalamocortical neural field model to investigate the effects of TRN on occurrence of SWD and its transition. Results show that the increasing inhibition from TRN to specific relay nuclei (SRN) can lead to the transition of system from SWD to slow-wave oscillation. Specially, it is shown that stimulations applied in the cortical neuronal populations can also initiate the SWD and slow-wave oscillation from the resting states under the typical inhibitory intensity from TRN to SRN. Then, we expand into a 3-compartment coupled thalamocortical model network in linear and circular structures, respectively, to explore the spatiotemporal evolutions of wave states in different compartments. The main results are: (i) for the open-ended model network, SWD induced by stimulus in the first compartment can be transformed into sleep-like slow UP-DOWN and spindle states as it propagates into the downstream compartments; (ii) for the close-ended model network, weak stimulations performed in the first compartment can result in the consistent experimentally observed spindle oscillations in all three compartments; in contrast, stronger periodic single-pulse stimulations applied in the first compartment can induce periodic transitions between SWD and spindle oscillations. Detailed investigations reveal that multi-attractor coexistence mechanism composed of SWD, spindles and background state underlies these state evolutions. What’s more, in order to demonstrate the state evolution stability with respect to the topological structures of neural network, we further expand the 3-compartment coupled network into 10-compartment coupled one, with linear and circular structures, and nearest-neighbor (NN) coupled network as well as its realization of small-world (SW) topology via random rewiring, respectively. Interestingly, for the cases of linear and circular connetivities, qualitatively similar results were obtained in addition to the more irregularity of firings. However, SWD can be eventually transformed into the consistent low-amplitude oscillations for both NN and SW networks. In particular, SWD evolves into the slow spindling oscillations and background tonic oscillations within the NN and SW network, respectively. Our modeling and simulation studies highlight the effect of network topology in the evolutions of SWD and spindling oscillations, which provides new insights into the mechanisms of cortical seizures development.     

Influence of transcranial magnetic stimulation on spike-wave discharges in a genetic model of absence epilepsy

Transcranial magnetic stimulation (TMS) impulses, (0.5 Hz, 3 impulses) were presented at threshold intensity to male WAG/Rij rats. One group received stimuli, which involved motor responses of hindlimbs, rats of the second group received sham stimulation. Electrocorticograms (ECoG) were recorded before and up to 2 hr from the moment of transcranial magnetic stimulation. It was established that such stimulation engendered a reduction of spike-wave discharge (SWD) bursts duration. This effect was most pronounced in 30 min from the moment of cessation of stimulation, when a decrease of 31.4% was noted in comparison with sham-stimulated control group. The number of bursts of spike-wave discharges was reduced, but did not reach significant difference when compared both with pre-stimulative base-line level and with sham-stimulated control rats. Bursts of spike-wave discharges restored up to pre-stimulative level in 90-150 minutes from the moment of cessation of transcranial stimulation. It can be concluded that transcranical magnetic stimulation possessed an ability to engender short-time suppression of bursts of spike-wave discharges in WAG/Rij rats.     

Two types of "spike-wave" discharges in the electrocorticogram of WAG/Rij rats, the genetic model of absence epilepsy

WAG/Rij rats were injected with apomorphine (0.5 mg/kg, i.p.), an agonist of D2 receptors. Two types of spike-wave discharges (generalized and local) were found in the baseline ECoG of the intact and injected rats. Injections of apomorphine led to a suppression of the generalized (type 1) for about 30 minutes and a 8-10-fold increase in the local spike-wave discharges (type 2) within 4-6 minutes. Since it has been shown earlier that haloperidol, which acts on dopamine receptors oppositely to apomorphine, enhance the generalized spike-wave activity and suppress the local discharges. Thus, the different pharmacological characteristics of the two types of spike-wave activity suggest the controlling role of the dopaminergic system in the processes of spike-wave generation.     

Hypothesis: a model for generalised autoimmunity

A detailed mechanism for the development of generalised autoimmunity is suggested, and the significance of the association between autoimmunity and leukemia is discussed.     

The properties of high-current high-pressure discharges

The properties of high-current high-pressure gas discharges (I = 60 kA, p = 1 atm, τ_1/2 = 1.6 ms, r ～ 10 cm) just before the end of the discharge are investigated experimentally. It is shown that the anomalously high rate of gas cooling after the current is switched off is related to the turbulent hydrodynamic processes induced by the Rayleigh-Taylor instability at the discharge boundary in the stage of volume radiative cooling of the discharge channel. The turbulent thermal conductivity is estimated using experimental data on the recovery of the electric strength of the discharge gap.     

On the theory of microwave discharges excited on the surface of a dielectric antenna

Microwave gas discharges excited near a dielectric surface are investigated. Such discharges can exist over a broad range of gas pressures and thereby can be used to solve a wide variety of applied problems. The wave dispersion properties favorable for discharge excitation are analyzed, and a kinetic discharge model is considered that can be used to calculate the discharge parameters. A model of a steady discharge at gas pressures of 10²–10⁴ Pa is constructed.     

A generalised transducing bacteriophage for Rhodococcus erythropolis

Summary Q4, a bacteriophage isolated from soil, mediated the transduction of a number of unlinked markers in Rhodococcus erythropolis. Highest numbers of transductants were obtained at multiplicities of infection of over 100, transductants only being obtained because of the temperate nature of the phage. Under optimal conditions, transduction to prototrophy of auxotrophic markers was over 50 times the spontaneous reversion rate and transduction of some antibitic resistance markers was over 10 times the spontaneous mutation rate. Segregation of unselected, but linked, markers was observed and the phage was used to order loci in a three factor cross. The virus required magnesium ions. Highest phage titres and greatest transduction frequency were obtained with stationary phase cultures.     

Capillary discharges for guiding of laser pulses

The dynamics of a capillary discharge is studied to achieve optimum conditions for the guiding of ultrashort intense laser pulses. A dynamic regime is revealed in which, after a short transient process, the discharge plasma is in dynamic and thermal equilibrium. Such plasma configuration is stable against MHD perturbations. It is shown that the radial inhomogeneity of the discharge plasma composition can provide the improvement of the focusing properties of a plasma waveguide. The radius of the region where electromagnetic radiation is localized is governed by a contact discontinuity between the plasma that initially fills the channel and the plasma that is produced due to ablation of the capillary wall material.