Theta rhythmicity enhances learning in adaptive STDP

The classical STDP window captures changes of a synaptic weight in response to the relative timing of a pre and a postsynaptic spike (see e.g. Bi and Poo, 1998). Due to its static nature, however, it cannot account for nonlinear interactions between spikes. Several theoretical studies offer dynamic formulations for STDP, for example by modulating the synaptic weight change by variables like synaptic calcium concentration (Shouval et al., 2002) or somatic depolarisation (Clopath et al., 2010), or by introducing spike triplet interactions (Pfister and Gerstner, 2006). Here, we propose a new model which is formulated as a set of differential equations (Schmiedt et al., 2010). The weight change is given by a differential Hebbian learning rule, which reproduces the STDP window for spike pairs. To account for the effects of repeated neuronal firing on the synaptic weight, we introduce modulations of the spike impact, which act on exponential traces of the spiking activity. We found that this model captures a series of experiments on STDP with complex spike pattern in cortex (Froemke et al., 2006) and hippocampus (Wang et al., 2005). When applied to continuous firing rates, our approach allows us to analyze the effects of given time courses of firing rates on the synaptic weight change, i.e. the filter properties of STDP. For sinusoidal modulations of baseline firing rates we find the strongest weight changes for modulation frequencies in the theta band, which plays a key role in learning. Furthermore, weight modifications in the hippocampus are predicted to be most prominent for baseline rates of around 5Hz in striking agreement with experimental findings.
This suggests that STDP-dependent learning is mediated by theta oscillations and modulated by the background firing rate which are both testable predictions of our theory

Gefangen im Regime. Diskussion: Ein neuer Sammelband über Regime verbindet Kunst, Politik und Kritik

Wie Herrschaft kritisieren, wenn Kategorien wie Staat, Souveränität und Demokratie nicht mehr funktionieren? Der Regimebegriff verspricht einen Ausweg aus diesem praktischen wie theoretischen Dilemma. Er soll nicht nur helfen, Macht und Herrschaft besser zu verstehen, sondern auch eine neue Grundlage für tiefere und radikalere Gesellschaftskritik bieten: Das Denken in Regimen bezieht Denk- und Wahrnehmungsmuster in die Analyse und Kritik von gesellschaftlichen Strukturen, (politischer) Macht und alltäglichen Normen und Praxen ein. Kurz: Regimeanalysen helfen uns zu sehen, was sonst unsichtbar bliebe, wie etwa die rassistische Regulierung von Migration, die Normierung von Geschlechterverhältnissen oder die Neoliberalisierung von Universitäten. Es wundert nicht, dass ein Begriff, mit dem solch verschiedene Phänomene beschrieben werden können, »sehr weitläufig und oft ungenau und spekulativ« ist. Die AutorInnen aus dem Umfeld der Wiener Akademie der Künste führen deshalb in ihren Buchbeiträgen zunächst in die unterschiedlichen Regimebegriffe ein und möchten untersuchen, »welchen diskursiven und politischen Gewinn er verspricht und tatsächlich bringt.

Studium doutnavého výboje v kyslíku a jeho směsích za středních tlaků

Title: Study of Glow Discharge in Oxygen and its Mixtures at Medium Pressures Author: Lukáš Schmiedt Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Věra Hrachová, CSc. Department of Surface and Plasma Science Abstract: The positive column of DC glow discharge sustained in oxygen and oxygen-argon mixtures has been studied in two discharge tubes of the same shape made from different materials (Silica and Pyrex glass) for total pressures 200 - 1750 Pa and discharge currents up to 40 mA. Parameters of the discharge - electric field strength and emission spectra - were studied with respect to existence of the low- and high-gradient forms of the positive column of the discharge. We have focused on the qualitative analysis of the differences in emission spectra for both particular forms, as well as on possibility of determination of the rotational temperature of oxygen molecule under various discharge conditions, particularly with respect to the relative amount of the admixture. Keywords: glow discharge; oxygen; medium pressures; emission spectraNázev práce: Studium doutnavého výboje v kyslíku a jeho směsích za středních tlaků Autor: Lukáš Schmiedt Katedra / Ústav: Katedra fyziky povrchů a plazmatu Vedoucí disertační práce: Doc. RNDr. Věra Hrachová, CSc. Katedra fyziky povrchů a plazmatu Abstrakt: Stejnosměrný doutnavý výboj v kyslíku a jeho směsích s argonem byl pro tlaky v rozmezí 200 - 1750 Pa a pro výbojové proudy do 40 mA zkoumán ve dvou výbojových trubicích stejného tvaru, avšak z různého materiálu (křemen a Pyrex). Šlo především o studium emisních spekter a podélného elektrického pole, a to s přihlédnutím k možné existenci vysokogradientní a nízkogradientní formy kladného sloupce doutnavého výboje. Náš výzkum byl zaměřen zejména na kvalitativní analýzu odlišností emisních spekter v obou formách výboje a dále na možnosti stanovení rotační teploty kyslíkové molekuly za různých výbojových podmínek, především v závislosti na množství příměsi. Klíčová slova: doutnavý výboj, kyslík, střední tlaky, emisní spektraKatedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Molecular symmetry, super-rotation, and semi-classical motion. New ideas for old problems

Customary theoretical models for molecular dynamics are based on a few fundamental assumptions like the commonly known ball-and-stick picture of molecular structure. In this work two examples of the limits of conventional molecular theory are discussed: Extremely floppy molecules where no equilibrium geometric structure is definable and molecules exhibiting highly excited rotational states, where the large angular momentum poses considerable challenges to quantum chemical calculations. For the extremely floppy molecules a fundamentally new zero-order description is established. The ‘super-rotor model’ is based on a five-dimensional rigid rotor treatment depending only on a single adjustable parameter. The respective quantum numbers define a generalized angular momentum which collectively describe internal and overall rotational motion. It consistently predicts the symmetry and energies of (most of) the low-energy states of the prototype of floppy molecules, protonated methane, which were only recently found experimentally. For highly excited rotational states, a path-integral based semi-classical treatment is shown to be capable of predicting energies and symmetries of quantized states even without sophisticated matrix diagonalization tools. In a proof-of-princinple study of sulfur dioxide, this analysis is shown to agree with advanced quantum chemical calculations. In addition, a straightforward and mathematically consistent method is developed to determine the nuclear spin permutation and rotational symmetry of molecules consisting of an arbitrary number of identical nuclei with any nuclear spin quantum number. This method is applied to formulate tentative symmetry-based selection rules and statistical state-to-state reaction rates for particular reactive collisions. In summary, fundamental symmetry considerations and semi-classical models are shown to contribute considerably to the understanding and extension of traditional concepts of molecular theory

Chronic kidney disease in aged cats: Clinical features, morphology, and proposed pathogeneses

Chronic kidney disease (CKD) is the most common metabolic disease of domesticated cats, with most affected cats being geriatric (>12 years of age). The prevalence of CKD in cats exceeds that observed in dogs, and the frequency of the diagnosis of CKD in cats has increased in recent decades. Typical histologic features include interstitial inflammation, tubular atrophy, and fibrosis with secondary glomerulosclerosis. In contrast to people and dogs, primary glomerulopathies with marked proteinuria are remarkably rare findings in cats. Although a variety of primary renal diseases have been implicated, the disease is idiopathic in most cats. Tubulointerstitial changes, including fibrosis, are present in the early stages of feline CKD and become more severe in advanced disease. A variety of factors—including aging, ischemia, comorbid conditions, phosphorus overload, and routine vaccinations—have been implicated as factors that could contribute to the initiation of this disease in affected cats. Factors that are related to progression of established CKD, which occurs in some but not all cats, include dietary phosphorus intake, magnitude of proteinuria, and anemia. Renal fibrosis, a common histologic feature of aged feline kidneys, interferes with the normal relationship between peritubular capillaries and renal tubules. Experimentally, renal ischemia results in morphologic changes similar to those observed in spontaneous CKD. Renal hypoxia, perhaps episodic, may play a role in the initiation and progression of this disease

Symmetry in the generalized rotor model for extremely floppy molecules

Protonated methane CH$_5^+$ is unique: It is an extremely fluxional molecule. All attempts to assign quantum numbers to the high-resolution transitions obtained over the last 20 years have failed because molecular rotation and vibration cannot be separated in the conventional way\footnote{Schmiedt, H., et al.{\it J. Chem. Phys.} {\bf 143} (15), 154302 (2015)}\footnote{Wodraszka, R. et al.{\it J. Phys. Chem. Lett.} {\bf 6}, 4229-4232 (2015)}. The first step towards a theoretical description is to include internal rotational degrees of freedom into the overall ones, which can be used to formulate a fundamentally new zero order approximation for the (now) generalized rotational states and energies. Predictions from this simple five-dimensional rotor model compare very favorably with the combination differences of protonated methane found in recent low temperature experiments\footnote{Asvany, O. et al.{\it Science}, {\bf 347}, (6228), 1346-1349 (2015)}. This talk will focus on symmetry aspects and implications of permutation symmetry for the generalized rotational states. Furthermore, refinements of the theory will be discussed, ranging from the generalization to even higher-dimensional rotors to explicit symmetry breaking and corresponding energy splittings. The latter includes the link to well-known theories of internal rotation dynamics and will show the general validity of the presented theory