Natural-gradient learning for spiking neurons.

In many normative theories of synaptic plasticity, weight updates implicitly depend on the chosen parametrization of the weights. This problem relates, for example, to neuronal morphology: synapses which are functionally equivalent in terms of their impact on somatic firing can differ substantially in spine size due to their different positions along the dendritic tree. Classical theories based on Euclidean-gradient descent can easily lead to inconsistencies due to such parametrization dependence. The issues are solved in the framework of Riemannian geometry, in which we propose that plasticity instead follows natural-gradient descent. Under this hypothesis, we derive a synaptic learning rule for spiking neurons that couples functional efficiency with the explanation of several well-documented biological phenomena such as dendritic democracy, multiplicative scaling, and heterosynaptic plasticity. We therefore suggest that in its search for functional synaptic plasticity, evolution might have come up with its own version of natural-gradient descent

Natural-gradient learning for spiking neurons

In many normative theories of synaptic plasticity, weight updates implicitly depend on the chosen parametrization of the weights. This problem relates, for example, to neuronal morphology: synapses which are functionally equivalent in terms of their impact on somatic firing can differ substantially in spine size due to their different positions along the dendritic tree. Classical theories based on Euclidean gradient descent can easily lead to inconsistencies due to such parametrization dependence. The issues are solved in the framework of Riemannian geometry, in which we propose that plasticity instead follows natural gradient descent. Under this hypothesis, we derive a synaptic learning rule for spiking neurons that couples functional efficiency with the explanation of several well-documented biological phenomena such as dendritic democracy, multiplicative scaling and heterosynaptic plasticity. We therefore suggest that in its search for functional synaptic plasticity, evolution might have come up with its own version of natural gradient descent.Comment: Joint senior authorship: Walter M. Senn and Mihai A. Petrovic

Chemical chain termination resolves the timing of ketoreduction in a partially reducing iterative type I polyketide synthase

Synthetic chain terminators were used to capture the biosynthetic intermediates from a partially reducing iterative type I polyketide synthase, which is integrated into a multimodular biosynthesis enzyme. The off-loaded metabolites clarified the timing of ketoreduction and aromatization in the assembly of the antibiotic micacocidin

Migrants in the media of the greater region SaarLorLux (1990-2010): A comparative content and discours analysis

Aufbauend auf einem aus dem Forschungsstand und seinen Defiziten abgeleiteten Mehrmethodenansatz richtet die Studie von Elena Kreutzer ihren Fokus auf die kulturwissenschaftliche Grenzgebiets-Forschung mit Blick auf Medienanalysen. Dabei liegt ihr thematischer Fokus auf der Darstellung von Migranten in den Printmedien Saarbrücker Zeitung, Républicain Lorrain und Luxemburger Wort der als hochgradig interkulturell umschriebenen europäischen Grenzregion SaarLorLux. Die inhalts- und diskursanalytischen Ergebnisse zeigten im Inter-Media-Vergleich folgende Einsichten und Erkenntnisse auf: Einerseits stellten sich über die inhaltsanalytischen Befunde heraus, dass sich die nationalen Systemkontexte in den Medieninhaltsanalysen zu journalistischen Darstellungsmerkmalen, Themenagenden sowie Handlungs- und Aussagenträgern widerspiegeln. Andererseits konnte die Arbeit über die Interdiskursanalyse übergreifende Denkmuster eruieren: Diese wurden in einem gemeinsamen Grundbestand an Kollektivsymbolen und Argumentationsmustern nachgewiesen, der von kulturenübergreifenden, aber dennoch medienspezifischen Elementen ergänzt wurde. Dabei zeigt sich in allen drei Printmedien, dass topische Muster nicht nur defensiv zur Abwehr restriktiver Bestimmungen bzw. Bestätigung vorherrschender Abwehrdiskurse verwendet wurden, sondern zeitweise auch offensiv zur Begründung zuzugs- oder integrationsfavorisierender Maßnahmen. Während auf Basis der Pro- und Contra-Tendenz in der saarländischen und lothringischen Tageszeitung jedoch ein verstärkt problem- und risikoorientierter Blick auf Migration und Migranten ermittelt wurde, richtete die luxemburgische Zeitung ihren Fokus phasenweise auf Potentiale und Ressourcen von Einwanderung und Vielfalt in Luxemburg. Die europäische Grenzregion als Ganzes in Betracht ziehende Zusammenhänge wurden weitgehend mittels grenzüberschreitender Hinweise in Sonderseiten hergestellt. Als Hinweis auf eine grenzüberschreitend kommunizierende Grenzregion genügt dieser Befund jedoch nich

Why women build less effective networks than men: The role of structural exclusion and personal hesitation

Studies have shown that women’s professional networks are often less powerful and effective than men’s in terms of exchanged benefits, yet the motivations that underlie the networking behaviours remain less well understood. Based on an interview study of 37 high-profile female leaders working in large German corporations, we found that not only the extrinsic barrier of structural exclusion from powerful networks, but also the intrinsic barrier of women’s hesitations to instrumentalize social ties are key to answering our research question: Why do women build less effective networks than men? Our analysis points to the existence of structural exclusion resulting from work–family conflict and homophily. With regard to personal hesitation, we identified two elements that were associated with under-benefiting from networking: moral considerations in social interactions and gendered modesty. Our study makes two important contributions. First, by highlighting personal hesitation as an intrinsic barrier, it extends the understanding of women’s motivations for networking based on social exchange theory. Second, based on structural barriers and personal hesitation, it develops a grounded theory model of networking that offers a holistic understanding of reasons that, from the perspective of the focal women, contribute to gender inequality in the workplace.</p