Ondrej Pokora | Masaryk University (original) (raw)
Papers by Ondrej Pokora
Bio Systems, Jan 4, 2015
Tinnitus is one of the leading disorders of hearing with no effective cure as its pathophysiologi... more Tinnitus is one of the leading disorders of hearing with no effective cure as its pathophysiological mechanisms remain unclear. While the sensitivity to sound is well-known to be affected, exactly how intensity coding per se is altered remains unclear. To address this issue, we used a salicylate-overdose animal model of tinnitus to measure auditory cortical evoked potentials at various stimulus levels, and analyzed on single-trial basis the response strength and its variance for the computation of the lower bound of Fisher information. Based on Fisher information profiles, we compared the precision or efficiency of intensity coding before and after salicylate-treatment. We found that after salicylate treatment, intensity coding was unexpectedly improved, rather than impaired. Also, the improvement varied in a sound-dependent way. The observed changes are likely due to some central compensatory mechanisms that are activated during tinnitus to bring out the full capacity of intensity ...
Lecture Notes in Computer Science, 2007
Several models for coding of odor intensity in olfactory sensory neurons are investigated. Behavi... more Several models for coding of odor intensity in olfactory sensory neurons are investigated. Behavior of the systems is described by stochastic processes of binding (and activation). Characteristics how well the odorant concentration can be estimated from the knowledge of response, the concentration of bounded (activated) neuron receptors, are studied. This approach is based on the Fisher information and analogous measures.
Lecture Notes in Computer Science, 2007
Abstract To study sensory neurons, the neuron response is plotted versus stimulus level. The aim ... more Abstract To study sensory neurons, the neuron response is plotted versus stimulus level. The aim of the present contribution is to determine how well two different levels of the incoming stimulation can be distinguished on the basis of their evoked responses. Two ...
PLoS ONE, 2011
During the stationary part of neuronal spiking response, the stimulus can be encoded in the firin... more During the stationary part of neuronal spiking response, the stimulus can be encoded in the firing rate, but also in the statistical structure of the interspike intervals. We propose and discuss two information-based measures of statistical dispersion of the interspike interval distribution, the entropy-based dispersion and Fisher information-based dispersion. The measures are compared with the frequently used concept of standard deviation. It is shown, that standard deviation is not well suited to quantify some aspects of dispersion that are often expected intuitively, such as the degree of randomness. The proposed dispersion measures are not entirely independent, although each describes the interspike intervals from a different point of view. The new methods are applied to common models of neuronal firing and to both simulated and experimental data.
Mathematical Biosciences, 2008
Several models (concentration detectors and a flux detector) for coding of odor intensity in olfa... more Several models (concentration detectors and a flux detector) for coding of odor intensity in olfactory sensory neurons are investigated. Behavior of the system is described by different stochastic processes of binding the odorant molecules to the receptors and their activation. Characteristics how well the odorant concentration can be estimated from the knowledge of response, the number of activated neurons, are studied. The approach is based on the Fisher information and analogous measures. These measures of optimality are computed and applied to locate the odorant concentration which is most suitable for coding. The results are compared with the classical deterministic approach which judges the optimal odorant concentration via steepness of the input-output function.
Brain Research, 2008
Neuronal responses evoked in sensory neurons by static stimuli of various intensities are usually... more Neuronal responses evoked in sensory neurons by static stimuli of various intensities are usually characterized by their input-output transfer function, i.e. by plotting the firing frequency (or any other measurable neuron response) versus the corresponding stimulus intensity. The aim of the present article is to determine the stimulus intensities which can be considered as "the most important" from two different points of view: transferring as much information as possible and coding the intensity as precisely as possible. These two problems are very different because, for example, an informative signal may be difficult to identify. We show that the role of noise is crucial in both problems. To obtain the range of stimuli which are the best identified, we propose to use measures based on Fisher information as known from the theory of statistical inference. To classify the most important stimuli from the point of view of information transfer, we suggest methods based on information theory. We show that both the most identifiable signal and the most informative signal are not unique. To study this, a generic model of input-output transfer function is analyzed under the influence of several different types of noise. Finally, the methods are illustrated on a model and data pertaining to olfactory sensory neurons.
BMC Neuroscience, 2009
Signal processing in olfactory systems is initiated by binding of odorant molecules to receptor m... more Signal processing in olfactory systems is initiated by binding of odorant molecules to receptor molecules embedded in the membranes of sensory neurons. Different models of olfactory sensory neurons (concentration detectors, flux detectors) have been investigated [1]. Their behavior is described by stochastic processes of binding and activation . The models assume that the response, concentration of activated receptors, is determined by the signal, the fixed log-concentration of odorant in perireceptor space. Dependency of the mean response on the signal is realized through the input-output function. How the concentration of activated receptors can code the intensity of odorant is analyzed using statistical properties of the steady-state responses. A deterministic approach to the problem of finding a suitable signal is based on the steepness of the input-output transfer function. The measure of optimality is the first derivative of the input-output function. For the usual sigmoidal shape, the best detectable signal is located at inflexion point of the curve.
BMC Neuroscience, 2011
We propose and discuss two information-based measures of statistical dispersion suitable to descr... more We propose and discuss two information-based measures of statistical dispersion suitable to description of interspike interval data. The measures are compared with the standard deviation. Although the standard deviation is used routinely, we show that it is not well suited to quantify some aspects of dispersion which are often expected intuitively, such as the degree of randomness. The proposed dispersion measures are not mutually independent, however, each describes the firing regularity from a different point of view. We discuss relationships between the measures and describe their extreme values. We also apply the method to real experimental data from spontaneously active olfactory neurons of rats. Our results and conclusions are applicable to a wide range of situations where the distribution of a continuous positive random variable is of interest.
Journal of Neuroscience Methods, 2012
Statistical characteristics of multiple spike trains are studied. Presence of refractory period e... more Statistical characteristics of multiple spike trains are studied. Presence of refractory period enables identification of specific clusters of spikes. Individual firing rates are determined from the multiple spike train by two methods.
Bio Systems, Jan 4, 2015
Tinnitus is one of the leading disorders of hearing with no effective cure as its pathophysiologi... more Tinnitus is one of the leading disorders of hearing with no effective cure as its pathophysiological mechanisms remain unclear. While the sensitivity to sound is well-known to be affected, exactly how intensity coding per se is altered remains unclear. To address this issue, we used a salicylate-overdose animal model of tinnitus to measure auditory cortical evoked potentials at various stimulus levels, and analyzed on single-trial basis the response strength and its variance for the computation of the lower bound of Fisher information. Based on Fisher information profiles, we compared the precision or efficiency of intensity coding before and after salicylate-treatment. We found that after salicylate treatment, intensity coding was unexpectedly improved, rather than impaired. Also, the improvement varied in a sound-dependent way. The observed changes are likely due to some central compensatory mechanisms that are activated during tinnitus to bring out the full capacity of intensity ...
Lecture Notes in Computer Science, 2007
Several models for coding of odor intensity in olfactory sensory neurons are investigated. Behavi... more Several models for coding of odor intensity in olfactory sensory neurons are investigated. Behavior of the systems is described by stochastic processes of binding (and activation). Characteristics how well the odorant concentration can be estimated from the knowledge of response, the concentration of bounded (activated) neuron receptors, are studied. This approach is based on the Fisher information and analogous measures.
Lecture Notes in Computer Science, 2007
Abstract To study sensory neurons, the neuron response is plotted versus stimulus level. The aim ... more Abstract To study sensory neurons, the neuron response is plotted versus stimulus level. The aim of the present contribution is to determine how well two different levels of the incoming stimulation can be distinguished on the basis of their evoked responses. Two ...
PLoS ONE, 2011
During the stationary part of neuronal spiking response, the stimulus can be encoded in the firin... more During the stationary part of neuronal spiking response, the stimulus can be encoded in the firing rate, but also in the statistical structure of the interspike intervals. We propose and discuss two information-based measures of statistical dispersion of the interspike interval distribution, the entropy-based dispersion and Fisher information-based dispersion. The measures are compared with the frequently used concept of standard deviation. It is shown, that standard deviation is not well suited to quantify some aspects of dispersion that are often expected intuitively, such as the degree of randomness. The proposed dispersion measures are not entirely independent, although each describes the interspike intervals from a different point of view. The new methods are applied to common models of neuronal firing and to both simulated and experimental data.
Mathematical Biosciences, 2008
Several models (concentration detectors and a flux detector) for coding of odor intensity in olfa... more Several models (concentration detectors and a flux detector) for coding of odor intensity in olfactory sensory neurons are investigated. Behavior of the system is described by different stochastic processes of binding the odorant molecules to the receptors and their activation. Characteristics how well the odorant concentration can be estimated from the knowledge of response, the number of activated neurons, are studied. The approach is based on the Fisher information and analogous measures. These measures of optimality are computed and applied to locate the odorant concentration which is most suitable for coding. The results are compared with the classical deterministic approach which judges the optimal odorant concentration via steepness of the input-output function.
Brain Research, 2008
Neuronal responses evoked in sensory neurons by static stimuli of various intensities are usually... more Neuronal responses evoked in sensory neurons by static stimuli of various intensities are usually characterized by their input-output transfer function, i.e. by plotting the firing frequency (or any other measurable neuron response) versus the corresponding stimulus intensity. The aim of the present article is to determine the stimulus intensities which can be considered as "the most important" from two different points of view: transferring as much information as possible and coding the intensity as precisely as possible. These two problems are very different because, for example, an informative signal may be difficult to identify. We show that the role of noise is crucial in both problems. To obtain the range of stimuli which are the best identified, we propose to use measures based on Fisher information as known from the theory of statistical inference. To classify the most important stimuli from the point of view of information transfer, we suggest methods based on information theory. We show that both the most identifiable signal and the most informative signal are not unique. To study this, a generic model of input-output transfer function is analyzed under the influence of several different types of noise. Finally, the methods are illustrated on a model and data pertaining to olfactory sensory neurons.
BMC Neuroscience, 2009
Signal processing in olfactory systems is initiated by binding of odorant molecules to receptor m... more Signal processing in olfactory systems is initiated by binding of odorant molecules to receptor molecules embedded in the membranes of sensory neurons. Different models of olfactory sensory neurons (concentration detectors, flux detectors) have been investigated [1]. Their behavior is described by stochastic processes of binding and activation . The models assume that the response, concentration of activated receptors, is determined by the signal, the fixed log-concentration of odorant in perireceptor space. Dependency of the mean response on the signal is realized through the input-output function. How the concentration of activated receptors can code the intensity of odorant is analyzed using statistical properties of the steady-state responses. A deterministic approach to the problem of finding a suitable signal is based on the steepness of the input-output transfer function. The measure of optimality is the first derivative of the input-output function. For the usual sigmoidal shape, the best detectable signal is located at inflexion point of the curve.
BMC Neuroscience, 2011
We propose and discuss two information-based measures of statistical dispersion suitable to descr... more We propose and discuss two information-based measures of statistical dispersion suitable to description of interspike interval data. The measures are compared with the standard deviation. Although the standard deviation is used routinely, we show that it is not well suited to quantify some aspects of dispersion which are often expected intuitively, such as the degree of randomness. The proposed dispersion measures are not mutually independent, however, each describes the firing regularity from a different point of view. We discuss relationships between the measures and describe their extreme values. We also apply the method to real experimental data from spontaneously active olfactory neurons of rats. Our results and conclusions are applicable to a wide range of situations where the distribution of a continuous positive random variable is of interest.
Journal of Neuroscience Methods, 2012
Statistical characteristics of multiple spike trains are studied. Presence of refractory period e... more Statistical characteristics of multiple spike trains are studied. Presence of refractory period enables identification of specific clusters of spikes. Individual firing rates are determined from the multiple spike train by two methods.