Graeme Clark Collection
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ItemCalculation of interspike intervals for integrate-and-fire neurons with Poisson distribution of synaptic inputs( 2000)We present a new technique for calculating the interspike intervals of integrate-and-fire neurons. There are two new components to this technique. First, the probability density of the summed potential is calculated by integrating over the distribution of arrival times of the afferent postsynaptic potentials (PSPs), rather than using conventional stochastic differential equation techniques. A general formulation of this technique is given in terms of the probability distribution of the inputs and the time course of the postsynaptic response. The expressions are evaluated in the gaussian approximation, which gives results that become more accurate for large numbers of small-amplitude PSPs. Second, the probability density of output spikes, which are generated when the potential reaches threshold, is given in terms of an integral involving a conditional probability density. A.N. Burkitt and G.M. Clark, 'Calculation of Interspike Intervals for Integrate and Fire Neurons with Poisson Distribution of Synaptic Inputs ', Neural Computation, 12:8 (August, 2000), pp. 1789-1820. © 2000 by the Massachusetts Institute of Technology. http://www.mitpressjournals.org.ezp.lib.unimelb.edu.au/toc/neco/12/8
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ItemElectrical stimulation of the auditory nerve with a cochlear implant and the temporal coding of sound frequencies: a brief review( 1997)There is considerable evidence that the brain translates (encodes) the frequency of a sound into both place of excitation (place encoding), and the pattern of intervals between action potentials (temporal encoding). Furthermore, temporal encoding is now thought to be due to a temporal as well as spatial pattern of action potentials in a small group of neurons. This pattern needs to be reproduced with a cochlear implant for improved speech processing. Our recent research has also demonstrated that the timing of excitatory postsynaptic potentials seen with intracellular recordings from brain cells, rather than extracellularly recorded action potentials, correlates better with the frequency of sound. These excitatory postsynaptic potentials are likely to be the link between the patterns of action potentials arriving at nerve cells and the biomolecular activity in the cell. This response also needs to be replicated with improved speech processing strategies.
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ItemA multi-threshold neural network for frequency estimation( 1996)Human perception of sound arises from the transmission of action-potentials (APs) through a neural network consisting of the auditory nerve and elements of the brain. Analysis of the response properties of individual neurons provides information regarding how features of sounds are coded in their firing patterns, and hints as to how higher brain centres may decode these neural response patterns to produce a perception of sound. Auditory neurons differ in the frequency of sound to which they respond most actively (their characteristic frequency), in their spontaneous (zero input) response, and also in their onset and saturation thresholds. Experiments have shown that neurons with low spontaneous rates show enhanced responses to the envelopes of complex sounds, while fibres with higher spontaneous rates respond to the temporal fine structure. In this paper, we determine an expression for the Cramer-Rao bound for frequency estimation of the envelope and fine structure of complex sounds by groups of neurons with parameterised response properties. The estimation variances are calculated for some typical estimation tasks, and demonstrate how, in the examples studied, a combination of low and high threshold fibres does not improve the estimation performance of a fictitious 'efficient' observer, but may improve the estimation performance of neural systems, such as biological neural networks, which are based on the detection of dominant interspike times.