Short Term Synaptic Depression Imposes a Frequency Dependent Filter on Synaptic Information Transfer

Depletion of synaptic neurotransmitter vesicles induces a form of short term depression in synapses throughout the nervous system. This plasticity affects how synapses filter presynaptic spike trains. The filtering properties of short term depression are often studied using a deterministic synapse model that predicts the mean synaptic response to a presynaptic spike train, but ignores variability introduced by the probabilistic nature of vesicle release and stochasticity in synaptic recovery time. We show that this additional variability has important consequences for the synaptic filtering of presynaptic information. In particular, a synapse model with stochastic vesicle dynamics suppresses information encoded at lower frequencies more than information encoded at higher frequencies, while a model that ignores this stochasticity transfers information encoded at any frequency equally well. This distinction between the two models persists even when large numbers of synaptic contacts are considered. Our study provides strong evidence that the stochastic nature neurotransmitter vesicle dynamics must be considered when analyzing the information flow across a synapse

Currency Unions

A currency union is when several independent sovereign nations share a common currency. This has been a recurring phenomenon in monetary history. In this article I study the theoretical foundations of such unions, and discuss some important currency unions in history, most notably the case of the US. Finally I contrast the design of the EMU with economic theories and historical experiences of currency unions

Currency Unions

Currency unions have been a recurring phenomenon in monetary history. The most basic definition of a currency union is when two or more sovereign nations share a common currency. Even though a currency union shares many characteristics with international monetary regimes based on fixed exchange rates (such as the Bretton Wood system), it is the most extreme case of a fixed exchange rate as it also implies sharing a common unit of account between the participating countries. While the economic rationale for currency unions focuses on gains in monetary efficiency from decreasing transaction costs, history shows that political reasons also played a key role. In this chapter, I discuss the theoretical foundations of monetary unions (the so-called optimum currency area theory) and analyze the most important historical cases of currency unification, both domestic (the USA, Germany) and international. Finally I discuss the key lessons we can draw from the history of currency unions and their implications for the Economic and Monetary Union