Intermittent spike-wave dynamics in a heterogeneous, spatially extended neural mass model

Generalised epileptic seizures are frequently accompanied by sudden, reversible transitions from low amplitude, irregular background activity to high amplitude, regular spike-wave discharges (SWD) in the EEG. The underlying mechanisms responsible for SWD generation and for the apparently spontaneous transitions to SWD and back again are still not fully understood. Specifically, the role of spatial cortico-cortical interactions in ictogenesis is not well studied. We present a macroscopic, neural mass model of a cortical column which includes two distinct time scales of inhibition. This model can produce both an oscillatory background and a pathological SWD rhythm. We demonstrate that coupling two of these cortical columns can lead to a bistability between out-of-phase, low amplitude background dynamics and in-phase, high amplitude SWD activity. Stimuli can cause state-dependent transitions from background into SWD. In an extended local area of cortex, spatial heterogeneities in a model parameter can lead to spontaneous reversible transitions from a desynchronised background to synchronous SWD due to intermittency. The deterministic model is therefore capable of producing absence seizure-like events without any time dependent adjustment of model parameters. The emergence of such mechanisms due to spatial coupling demonstrates the importance of spatial interactions in modelling ictal dynamics, and in the study of ictogenesis.

Risk factors for reperfusion injury after lung transplantation

OBJECTIVE: To assess the influence of recipient's and donor's factors as well as surgical events on the occurrence of reperfusion injury after lung transplantation. DESIGN AND SETTING: Retrospective study in the surgical intensive care unit (ICU) of a university hospital. METHODS: We collected data on 60 lung transplantation donor/recipient pairs from June 1993 to May 2001, and compared the demographic, peri- and postoperative variables of patients who experienced reperfusion injury (35%) and those who did not. RESULTS: The occurrence of high systolic pulmonary pressure immediately after transplantation and/or its persistence during the first 48[Symbol: see text]h after surgery was associated with reperfusion injury, independently of preoperative values. Reperfusion injury was associated with difficult hemostasis during transplantation (p[Symbol: see text]=[Symbol: see text]0.03). Patients with reperfusion injury were more likely to require the administration of catecholamine during the first 48[Symbol: see text]h after surgery (p[Symbol: see text]=[Symbol: see text]0.014). The extubation was delayed (p[Symbol: see text]=[Symbol: see text]0.03) and the relative odds of ICU mortality were significantly greater (OR 4.8, 95% CI: 1.06, 21.8) in patients with reperfusion injury. Our analysis confirmed that preexisting pulmonary hypertension increased the incidence of reperfusion injury (p[Symbol: see text]<[Symbol: see text]0.01). CONCLUSIONS: Difficulties in perioperative hemostasis were associated with reperfusion injury. Occurrence of reperfusion injury was associated with postoperative systolic pulmonary hypertension, longer mechanical ventilation and higher mortality. Whether early recognition and treatment of pulmonary hypertension during transplantation can prevent the occurrence of reperfusion injury needs to be investigated.

Cortical local and long-range synchronization interplay in human absence seizure initiation

Brain activity relies on transient, fluctuating interactions between segregated neuronal populations. Synchronization within a single and between distributed neuronal clusters reflects the dynamics of these cooperative patterns. Thus absence epilepsy can be used as a model for integrated, large-scale investigation of the emergence of pathological collective dynamics in the brain. Indeed, spike-wave discharges (SWD) of an absence seizure are thought to reflect abnormal cortical hypersynchronization. In this paper, we address two questions: how and where do SWD arise in the human brain? Therefore, we explored the spatio-temporal dynamics of interactions within and between widely distributed cortical sites using magneto-encephalographic recordings of spontaneous absence seizures. We then extracted, from their time-frequency analysis, local synchronization of cortical sources and long-range synchronization linking distant sites. Our analyses revealed a reproducible sequence of 1) long-range desynchronization, 2) increased local synchronization and 3) increased long-range synchronization. Although both local and long-range synchronization displayed different spatio-temporal profiles, their cortical projection within an initiation time window overlap and reveal a multifocal fronto-central network. These observations contradict the classical view of sudden generalized synchronous activities in absence epilepsy. Furthermore, they suggest that brain states transition may rely on multi-scale processes involving both local and distant interactions.

Why Death Matters: Understanding Gameworld Experience

This article presents a study of the staging and implementation of death and the death penalty in a number of popular MMOGs and relates it to players general experience of gameworlds. Game mechanics, writings and stories by designers and players, and the results of an online survey are analysed and discussed. The study shows that the death penalty is implemented much in the same way across worlds; that death can be both trivial and non-trivial, part of the grind of everyday life, or essential in the creation of heroes, depending on context. In whatever function death may serves, it is argued that death plays an important part in the shaping and emergence of the social culture of a world, and in the individual players experience of life within it.