Closed-Form Treatment of the Interactions between Neuronal Activity and Timing-Dependent Plasticity in Networks of Linear Neurons

Network activity and network connectivity mutually influence each other. Especially for fast processes, like spike-timing-dependent plasticity (STDP), which depends on the interaction of few (two) signals, the question arises how these interactions are continuously altering the behavior and structure of the network. To address this question a time-continuous treatment of plasticity is required. However, this is - even in simple recurrent network structures - currently not possible. Thus, here we develop for a linear differential Hebbian learning system a method by which we can analytically investigate the dynamics and stability of the connections in recurrent networks. We use noisy periodic external input signals, which through the recurrent connections lead to complex actual ongoing inputs and observe that large stable ranges emerge in these networks without boundaries or weight-normalization. Somewhat counter-intuitively, we find that about 40% of these cases are obtained with a long-term potentiation-dominated STDP curve. Noise can reduce stability in some cases, but generally this does not occur. Instead stable domains are often enlarged. This study is a first step toward a better understanding of the ongoing interactions between activity and plasticity in recurrent networks using STDP. The results suggest that stability of (sub-)networks should generically be present also in larger structures

Neuere Untersuchungen zur Prädiktion von EEG-Signalen bei Epilepsie

Seit einigen Jahren ist die Analyse von EEG-Signalen bei Epilepsie Gegenstand zahlreicher wissenschaftlicher Arbeiten; Zielvorstellung ist dabei die Entwicklung von Verfahren zur Erkennung eines möglichen Voranfallszustandes. Im Vordergrund steht beispielsweise die Approximation einer so genannten effektiven Korrelationsdimension, die Bestimmung der maximalen Lyapunov-Exponenten, Detektionsverfahren für Muster bei Zellularen Nichtlinearen Netzwerken, die Bestimmung der mittleren Phasenkohärenz und Verfahren zur nichtlinearen Prädiktion von EEG-Signalen. Trotz umfangreicher Bemühungen kann bis heute eine Erkennung von Anfallsvorboten mit einer Sensitivität und Spezifität, die eine automatisierte Anfallsvorhersage ermöglichen würde, noch nicht durchgeführt werden. In diesem Beitrag werden neue Ergebnisse zur Prädiktion von EEG-Signalen bei Epilepsie vorgestellt. Dabei werden Signale, welche mittels intrakranieller electrocorticographischer (ECoG) und stereoelectroencephalographischer (SEEG) Ableitungen registriert wurden, segmentweise analysiert. Unter der Annahme, dass sich Änderungen des Systems ,,Gehirn" als Änderungen im Prädiktor, d.h. in seinen Systemparametern widerspiegeln, könnte eine nähere Betrachtung der Prädiktoreigenschaften zu einer Erkennung von Anfallsvorboten führen

Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions

Acknowledgments We thank the European Research Council (ERC; project GA 335910 VEWA) and Natural Environment Research Council (NERC; project NE/K000268/1) for funding. We would like to thank Konrad Piegat for invaluable help with the fieldwork. Iain Malcolm and staff at Marine Scotland (Pitlochry) are also thanked for the provision of data from the AWS. We also thank three anonymous reviewers for their constructive comments.Peer reviewedPublisher PD

Using SAS functions and high resolution isotope data to unravel travel time distributions in headwater catchments

Acknowledgments. We are grateful to the European Research Council (ERC) VeWa project (GA335910) and NERC/JIP SIWA project (NE/MO19896/1) for funding. A.R. acknowledges the financial support from the ENAC school at EPFL. C.B. acknowledges support from the University of Costa Rica (project 217-B4-239 and the Isotope Network for Tropical Ecosystem Studies (ISONet)). Data to support this study are provided by the Northern Rivers Institute, University of Aberdeen and are available by the authors. The authors wish to thank Ype van der Velde, Arash Massoudieh, Jean-Raynald de Dreuzy and an anonymous referee for the useful review comments.Peer reviewedPublisher PD