119 research outputs found
How Noisy Adaptation of Neurons Shapes Interspike Interval Histograms and Correlations
Channel noise is the dominant intrinsic noise source of neurons causing variability in the timing of action potentials and interspike intervals (ISI). Slow adaptation currents are observed in many cells and strongly shape response properties of neurons. These currents are mediated by finite populations of ionic channels and may thus carry a substantial noise component. Here we study the effect of such adaptation noise on the ISI statistics of an integrate-and-fire model neuron by means of analytical techniques and extensive numerical simulations. We contrast this stochastic adaptation with the commonly studied case of a fast fluctuating current noise and a deterministic adaptation current (corresponding to an infinite population of adaptation channels). We derive analytical approximations for the ISI density and ISI serial correlation coefficient for both cases. For fast fluctuations and deterministic adaptation, the ISI density is well approximated by an inverse Gaussian (IG) and the ISI correlations are negative. In marked contrast, for stochastic adaptation, the density is more peaked and has a heavier tail than an IG density and the serial correlations are positive. A numerical study of the mixed case where both fast fluctuations and adaptation channel noise are present reveals a smooth transition between the analytically tractable limiting cases. Our conclusions are furthermore supported by numerical simulations of a biophysically more realistic Hodgkin-Huxley type model. Our results could be used to infer the dominant source of noise in neurons from their ISI statistics
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Crosslinked and crosslinkable hollow fiber mixed matrix membrane and method of making same
A composition of and a method of making high performance mixed matrix hollow fiber membranes is described. The membranes have a high resistance to plasticization by use of a predetermined amount of crosslinking. The preferred polymer material for the membrane is a polyimide polymer continuous phase comprising ester crosslinks and a molecular sieve material dispersed within the polymer continuous phase. The resultant mixed matrix hollow fiber membrane exhibits a high permeance of CO2 in combination with a high CO2/CH4 selectivity. Another embodiment provides a method of making the mixed matrix hollow fiber membrane from a monesterified polymer followed by final crosslinking after hollow fiber formation.Board of Regents, University of Texas Syste
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