A Markovian event-based framework for stochastic spiking neural networks

In spiking neural networks, the information is conveyed by the spike times, that depend on the intrinsic dynamics of each neuron, the input they receive and on the connections between neurons. In this article we study the Markovian nature of the sequence of spike times in stochastic neural networks, and in particular the ability to deduce from a spike train the next spike time, and therefore produce a description of the network activity only based on the spike times regardless of the membrane potential process. To study this question in a rigorous manner, we introduce and study an event-based description of networks of noisy integrate-and-fire neurons, i.e. that is based on the computation of the spike times. We show that the firing times of the neurons in the networks constitute a Markov chain, whose transition probability is related to the probability distribution of the interspike interval of the neurons in the network. In the cases where the Markovian model can be developed, the transition probability is explicitly derived in such classical cases of neural networks as the linear integrate-and-fire neuron models with excitatory and inhibitory interactions, for different types of synapses, possibly featuring noisy synaptic integration, transmission delays and absolute and relative refractory period. This covers most of the cases that have been investigated in the event-based description of spiking deterministic neural networks

Upper critical field and de Haas-van Alphen oscillations in KOs2_2O6_6 measured in a hybrid magnet

Magnetic torque measurements have been performed on a KOs$_2$O$_6$ single crystal in magnetic fields up to 35.3 T and at temperatures down to 0.6 K. The upper critical field is determined to be $\sim$30 T. De Haas-van Alphen oscillations are observed. A large mass enhancement of (1+$\lambda$) = $m^* / m_{band}$ = 7.6 is found. It is suggested that, for the large upper critical field to be reconciled with Pauli paramagnetic limiting, the observed mass enhancement must be of electron-phonon origin for the most part.Comment: 4 pages, 4 figures, published versio

The views and experiences of suicidal children and young people of mental health support services: A meta-ethnography.

Background: Suicide is amongst the leading causes of death in young people globally and a health priority worldwide. For children and young people (CYP) attempting or considering suicide there is no agreed treatment model. Development of treatment models should be informed by the views and experiences of CYP using services. Methods: Meta-ethnography was used to systematically identify and synthesise studies reporting the views of CYP who used mental health services following suicidal behaviour. Relevant studies were quality appraised. First order (participants) and second order (original author) data were translated to identify common and disconfirming themes and concepts. Translated findings were synthesised and led to a new hypothesis supported by additional ‘linguistic analysis’ of texts to construct a novel third order line-of-argument. Results: Four studies conducted since 2006 in three countries involving 44 young people aged 11-24 years were synthesised. Translation revealed that suicidal CYP do not know where or how to access help, they cannot access help directly and when seen by mental health practitioners they do not feel listened to. Line-of-argument synthesis identified a silence around suicidality within the conversations CYP have with mental health practitioners and within academic research reporting. Use of the term ‘self-harm’ to encompass suicidal behaviours potentially contributes to this silence by avoiding the word ‘suicide’. Conclusions: CYP who are suicidal need to have easy access to mental health services. When using services, they want to feel listened to and have suicidal feelings acknowledged. This involves professionals referring explicitly to suicide not just self-harm

Using photo-elicitation to understand reasons for repeated self-harm: a qualitative study

Background: Reasons for self-harm are not well understood. One of the reasons for this is that first-hand accounts are usually elicited using traditional interview and questionnaire methods. This study aims to explore the acceptability of using an approach (photo-elicitation) that does not rely on solely verbal or written techniques, and to make a preliminary assessment of whether people can usefully employ images to support a discussion about the reasons why they self-harm. Method: Interviews with eight participants using photo elicitation, a method in which photographs produced by the participant are used as a stimulus and guide within the interview. Results: Participants responded positively to using images to support a discussion about their self-harm and readily incorporated images in the interview. Four main themes were identified representing negative and positive or adaptive purposes of self-harm: self-harm as a response to distress, self-harm to achieve mastery, self-harm as protective and self-harm as a language or form of communication. Conclusions: Employing this novel approach was useful in broadening our understanding of self-harm

Relations parents-adolescents autour des automutilations : une étude qualitative

International audienceObjectivesNon-suicidal self-injury (NSSI) is a frequent issue during adolescence responsible for many difficulties in the relationship between parents and adolescents. This study explores the function of self-harm in parent-adolescent relationships.MethodsThis is a qualitative study based on semi-structured interviews with adolescents, who are receiving psychiatric care for DSH (deliberate self harm), and their parents. Data are analysed using the Interpretative Phenomenological Analysis.ResultsTwenty-five interviews were carried out with 11 adolescents and 14 parents. Ten themes were organized around three super-ordinate themes. The relationship difficulties between parents and adolescents are marked by the lack of communication, fragile links and great difficulty to trust one another. The discovery of DSH behaviour by the parents triggers an emotional turmoil described as an extremely violent experience associated with very painful feelings. Finally, parents describe a change in the family dynamics induced by DSH. These changes are perceptible through a movement of independence and regaining of the control from the adolescent, and a wish for mutual protection of adolescents and their parents. Including parents more in the therapeutic care, both as an impacted person and at the same time as a co therapist, appears to be indispensable.Buts de l’étudeLes automutilations sont fréquentes à l’adolescence et génèrent de nombreuses difficultés relationnelles entre parents et adolescents. Nous proposons dans cette étude d’explorer la fonction des automutilations au cœur de la relation parent-adolescent.Patient et méthodeIl s’agit d’une étude qualitative basée sur des entretiens semi-structurés auprès d’adolescents suivis en pédopsychiatrie pour des automutilations et de leurs parents analysés avec la méthode Interpretative Phenomenological Analysis.RésultatsVingt cinq entretiens ont été recueillis (11 adolescents, 14 parents). Ils ont permis de dégager 10 thèmes que nous avons classés en trois méta-thèmes : les difficultés relationnelles entre parents et adolescents, le bouleversement émotionnel induit par la découverte des automutilations, et les réorganisations relationnelles secondaires à la découverte des automutilations.ConclusionsLa dynamique familiale est largement modifiée par la découverte des automutilations. La souffrance des parents, leur incompréhension, et leur demande d’aide est importante à entendre dans le soin. Les automutilations mettent en évidence des liens familiaux fragiles, et les parents souvent désemparés essaient de reprendre le contrôle de la situation par des réactions qui semblent parfois aggraver la souffrance des adolescents. Inclure les parents davantage dans la prise en charge thérapeutique, à la fois en tant que personne impactée et en même temps en tant que co thérapeute apparaît indispensable

First-passage problems for degenerate two-dimensional diffusion processes

Hitting place, hitting time, Brownian motion, Kolmogorov equation, Sturm-Liouville equation, 60J70, 60J60,