How adaptation currents change threshold, gain and variability of neuronal spiking

Many types of neurons exhibit spike rate adaptation, mediated by intrinsic slow $\mathrm{K}^+$-currents, which effectively inhibit neuronal responses. How these adaptation currents change the relationship between in-vivo like fluctuating synaptic input, spike rate output and the spike train statistics, however, is not well understood. In this computational study we show that an adaptation current which primarily depends on the subthreshold membrane voltage changes the neuronal input-output relationship (I-O curve) subtractively, thereby increasing the response threshold. A spike-dependent adaptation current alters the I-O curve divisively, thus reducing the response gain. Both types of adaptation currents naturally increase the mean inter-spike interval (ISI), but they can affect ISI variability in opposite ways. A subthreshold current always causes an increase of variability while a spike-triggered current decreases high variability caused by fluctuation-dominated inputs and increases low variability when the average input is large. The effects on I-O curves match those caused by synaptic inhibition in networks with asynchronous irregular activity, for which we find subtractive and divisive changes caused by external and recurrent inhibition, respectively. Synaptic inhibition, however, always increases the ISI variability. We analytically derive expressions for the I-O curve and ISI variability, which demonstrate the robustness of our results. Furthermore, we show how the biophysical parameters of slow $\mathrm{K}^+$-conductances contribute to the two different types of adaptation currents and find that $\mathrm{Ca}^{2+}$-activated $\mathrm{K}^+$-currents are effectively captured by a simple spike-dependent description, while muscarine-sensitive or $\mathrm{Na}^+$-activated $\mathrm{K}^+$-currents show a dominant subthreshold component.Comment: 20 pages, 8 figures; Journal of Neurophysiology (in press

Classification and Redshift Estimation in Multi-Color Surveys

We present a photometric method for identifying stars, galaxies and quasars in multi-color surveys and estimating multi-color redshifts for the extragalactic objects. We use a library of >65000 color templates for comparison with observed objects. The method was originally developed for the Calar Alto Deep Imaging Survey (CADIS), but is now used in a variety of survey projects. We checked its performance by spectroscopy of CADIS objects, where it provides high reliability (6 mistakes among 151 objects with R<24), especially for the quasar selection, and redshifts accurate within sigma_z = 0.03 for galaxies and sigma_z = 0.1 for quasars. For an optimization of future surveys, a few model surveys are compared, which use the same amount of telescope time but different filter sets. In summary, medium-band surveys perform superior to broad-band surveys although they collect less photons. A full account of this work is already in print.Comment: 7 pages, 2 figures, proceedings of MPA/ESO/MPE Joint Astronomy Conference Mining THE SKY held in Garching, Germany, July 31 - Aug 4, 200

5G Positioning and Mapping with Diffuse Multipath

5G mmWave communication is useful for positioning due to the geometric connection between the propagation channel and the propagation environment. Channel estimation methods can exploit the resulting sparsity to estimate parameters(delay and angles) of each propagation path, which in turn can be exploited for positioning and mapping. When paths exhibit significant spread in either angle or delay, these methods breakdown or lead to significant biases. We present a novel tensor-based method for channel estimation that allows estimation of mmWave channel parameters in a non-parametric form. The method is able to accurately estimate the channel, even in the absence of a specular component. This in turn enables positioning and mapping using only diffuse multipath. Simulation results are provided to demonstrate the efficacy of the proposed approach

The Energy Landscape of Myoglobin: An Optical Study

In this paper we demonstrate how the potential energy surface of a protein, which determines its conformational degrees of freedom, can be constructed from a series of advanced nonlinear optical experiments. The energy landscape of myoglobin was probed by studying its low-temperature structural dynamics, using several spectral hole burning and photon echo techniques. The spectral diffusion of the heme group of the protein was studied on a time scale ranging from nanoseconds to several days while covering a temperature range from 100 mK to 23 K. The spectral line broadening, as measured in three-pulse stimulated photon echo experiments, occurs in a stepwise fashion, while the exact time dependence of the line width is critically dependent on temperature. From these results we obtained the energy barriers between the conformational states of the protein. Aging time dependent hole-burning experiments show that, at 100 mK, it takes several days for the protein to reach thermal equilibrium. When, after this period a spectral hole is burned, the line broadening induced by well-defined temperature cycles is partly reversed over a period of several hours. From this we conclude that a rough structure is superimposed on the overall shape of the potential energy surface of the protein. By combining the hole burning and photon echo results, we construct a detailed image of this energy landscape, supporting the general concept of a structural hierarchy. More specifically, we show that the number of conformational substates in the lower hierarchical tiers is much lower than was previously anticipated and, in fact, is comparable to the number of taxonomic substates.

How adaptation currents and synaptic inhibition change threshold, gain and variability of neuronal spiking : From Twenty Second Annual Computational Neuroscience Meeting: CNS*2013 Paris, France. 13-18 July 2013

Published by BioMed Central Ladenbauer, Josef ; Augustin, Moritz ; Obermayer, Klaus : How adaptation currents and synaptic inhibition change threshold, gain and variability of neuronal spiking. - In: BMC Neuroscience. - ISSN 1471-2202 (online). - 14 (2013), suppl. 1, P299. - doi:10.1186/1471-2202-14-S1-P299