Papers by Fernando Montani
Chaos: An Interdisciplinary Journal of Nonlinear Science
In this study, the Hénon map was analyzed using quantifiers from information theory in order to c... more In this study, the Hénon map was analyzed using quantifiers from information theory in order to compare its dynamics to experimental data from brain regions known to exhibit chaotic behavior. The goal was to investigate the potential of the Hénon map as a model for replicating chaotic brain dynamics in the treatment of Parkinson’s and epilepsy patients. The dynamic properties of the Hénon map were compared with data from the subthalamic nucleus, the medial frontal cortex, and a [Formula: see text]-DG model of neuronal input–output with easy numerical implementation to simulate the local behavior of a population. Using information theory tools, Shannon entropy, statistical complexity, and Fisher’s information were analyzed, taking into account the causality of the time series. For this purpose, different windows over the time series were considered. The findings revealed that neither the Hénon map nor the [Formula: see text]-DG model could perfectly replicate the dynamics of the brai...
The European Physical Journal B
Recent studies have shown that gamma-band oscillations are directly related to pain intensity. Pa... more Recent studies have shown that gamma-band oscillations are directly related to pain intensity. Pain can be exacerbated or diminished via deactivation or activation of inhibitory interneurons in the dorsal horn. We consider a biologically plausible network model with different proportion of inhibitory neurons to emulate gamma elicited activity during pain processes. We perform an analysis using graph theory to gain further insight in the functional state of the circuitry underlying nociceptive process, considering all the possible gamma elicited configurations of pain when changing the number of inhibitory neurons. The probability distribution of the signal associated with each node or neuron is estimated through the Bandt and Pompe approach. We evaluate the Jensen-Shannon distance between all the possible pairs of nodes/neurons, characterizing the different network configurations by calculating the closeness centrality. Thus, by building the graph properties through the node strength distributions and using an information theoretical approach, we characterize the dynamics of the network configurations of pain. This allows us to identify the nonlinear dynamical structure underlying the nociceptive process. Importantly, our findings show that a network configuration with a 20% of inhibitory neurons boosts information transmission of the complex network circuitry associated with the pain processing.
Chaos: An Interdisciplinary Journal of Nonlinear Science
Intracranial electroencephalography (iEEG) can directly record local field potentials (LFPs) from... more Intracranial electroencephalography (iEEG) can directly record local field potentials (LFPs) from a large set of neurons in the vicinity of the electrode. To search for possible epileptic biomarkers and to determine the epileptogenic zone that gives rise to seizures, we investigated the dynamics of basal and preictal signals. For this purpose, we explored the dynamics of the recorded time series for different frequency bands considering high-frequency oscillations (HFO) up to [Formula: see text] Hz. We apply a Hilbert transform to study the amplitude and phase of the signals. The dynamics of the different frequency bands in the time causal entropy-complexity plane, [Formula: see text], is characterized by comparing the dynamical evolution of the basal and preictal time series. As the preictal states evolve closer to the time in which the epileptic seizure starts, the, [Formula: see text], dynamics changes for the higher frequency bands. The complexity evolves to very low values and ...
Entropy
Synaptic plasticity is characterized by remodeling of existing synapses caused by strengthening a... more Synaptic plasticity is characterized by remodeling of existing synapses caused by strengthening and/or weakening of connections. This is represented by long-term potentiation (LTP) and long-term depression (LTD). The occurrence of a presynaptic spike (or action potential) followed by a temporally nearby postsynaptic spike induces LTP; conversely, if the postsynaptic spike precedes the presynaptic spike, it induces LTD. This form of synaptic plasticity induction depends on the order and timing of the pre- and postsynaptic action potential, and has been termed spike time-dependent plasticity (STDP). After an epileptic seizure, LTD plays an important role as a depressor of synapses, which may lead to their complete disappearance together with that of their neighboring connections until days after the event. Added to the fact that after an epileptic seizure the network seeks to regulate the excess activity through two key mechanisms: depressed connections and neuronal death (eliminating...
XXVII Jornadas de Jóvenes Investigadores de la Asociación de Universidades Grupo Montevideo (Brasil, 23 al 25 de octubre de 2019), 2019
Los tamaños estimados por DLS (Dynamic Light Scattering) fueron de 12±4nm, 25±9nm y 20±8nm para l... more Los tamaños estimados por DLS (Dynamic Light Scattering) fueron de 12±4nm, 25±9nm y 20±8nm para las NPa Ag sintetizadas con GA, FA y
The EEG is a non-invasive technique recorded on the scalp that often has a poor relationship to t... more The EEG is a non-invasive technique recorded on the scalp that often has a poor relationship to the spiking activity of individual neurons. Measures of the relative contribution of EEG oscillations are particularly useful to investigate the emergent properties of the rhythmic activities of the brain. The EEG records the electrical activity of the brain; sensory stimulation or motor output shows different oscillations bands including theta (∈ [4, 8) Hz), alpha (∈ [8, 13) Hz), beta (∈ [13, 31) Hz), and gamma ranges (∈ [31, 50) Hz). The different rhythms of the brain activity are of functional importance to understand how information is processed in the mammalian brain. In previous works we investigate the hypothesis that neural processes associated with visuomotor integration or imaginary task are related to a higher amount of complexity in certain frequency bands. In order to do so, we used the Bandt-Pompe (BP) permutation methodology for the evaluation of the probability distributio...
The Journal of Neuroscience, 2007
International Journal of Neural Systems, 2017
Whether premotor/motor neurons encode information in terms of spiking frequency or by their relat... more Whether premotor/motor neurons encode information in terms of spiking frequency or by their relative time of firing, which may display synchronization, is still undetermined. To address this issue, we used an information theory approach to analyze neuronal responses recorded in the premotor (area F5) and primary motor (area F1) cortices of macaque monkeys under four different conditions of visual feedback during hand grasping. To evaluate the sensitivity of spike timing correlation between single neurons, we investigated the stimulus dependent synchronization in our population of pairs. We first investigated the degree of correlation of trial-to-trial fluctuations in response strength between neighboring neurons for each condition, and second estimated the stimulus dependent synchronization by means of an information theoretical approach. We compared the information conveyed by pairs of simultaneously recorded neurons with the sum of information provided by the respective individual...
Journal of Neuroscience Methods
Entropy, 2020
A major challenge in neuroscience is to understand the role of the higher-order correlations stru... more A major challenge in neuroscience is to understand the role of the higher-order correlations structure of neuronal populations. The dichotomized Gaussian model (DG) generates spike trains by means of thresholding a multivariate Gaussian random variable. The DG inputs are Gaussian distributed, and thus have no interactions beyond the second order in their inputs; however, they can induce higher-order correlations in the outputs. We propose a combination of analytical and numerical techniques to estimate higher-order, above the second, cumulants of the firing probability distributions. Our findings show that a large amount of pairwise interactions in the inputs can induce the system into two possible regimes, one with low activity (“DOWN state”) and another one with high activity (“UP state”), and the appearance of these states is due to a combination between the third- and fourth-order cumulant. This could be part of a mechanism that would help the neural code to upgrade specific inf...
Frontiers in Physics, 2019
Entropy, 2018
The electroencephalogram (EEG) is an electrophysiological monitoring method that allows us to gli... more The electroencephalogram (EEG) is an electrophysiological monitoring method that allows us to glimpse the electrical activity of the brain. Neural oscillations patterns are perhaps the best salient feature of EEG as they are rhythmic activities of the brain that can be generated by interactions across neurons. Large-scale oscillations can be measured by EEG as the different oscillation patterns reflected within the different frequency bands, and can provide us with new insights into brain functions. In order to understand how information about the rhythmic activity of the brain during visuomotor/imagined cognitive tasks is encoded in the brain we precisely quantify the different features of the oscillatory patterns considering the Shannon–Fisher plane H × F . This allows us to distinguish the dynamics of rhythmic activities of the brain showing that the Beta band facilitate information transmission during visuomotor/imagined tasks.
Physica A: Statistical Mechanics and its Applications, 2018
We consider EEG signals of realized and imagined movements. • We need to infer the dynamical prop... more We consider EEG signals of realized and imagined movements. • We need to infer the dynamical properties of both tasks. • We use an information theory framework in combination with a wavelet decomposition. • Entropy-complexity plane allows distinguishing realized from imagined tasks.
Physical Review E, 2018
Experiments in certain regions of the cerebral cortex suggest that the spiking activity of neuron... more Experiments in certain regions of the cerebral cortex suggest that the spiking activity of neuronal populations is regulated by common non-Gaussian inputs across neurons. We model these deviations from random-walk processes with q-Gaussian distributions into simple threshold neurons, and investigate the scaling properties in large neural populations. We show that deviations from the Gaussian statistics provide a natural framework to regulate population statistics such as sparsity, entropy, and specific heat. This type of description allows us to provide an adequate strategy to explain the information encoding in the case of low neuronal activity and its possible implications on information transmission.
Physical Review E, 2016
The main contribution of this project is the development of a homogeneous model of a man to prese... more The main contribution of this project is the development of a homogeneous model of a man to presents the specific absorption rate (SAR) due to high power transmission line. As a low frequency application under high power transmission line of 50 Hz in electrical engineering, to studies the influence of human's posture on specific absorption rate. This project designs two types of human body which one design uses most cylinder block and another design use brick block where both blocks have a different value of mesh cells. For each design has four types of posture are standing, sitting, arms up and arms out by using Computer Simulation Technology (CST) Studio Software. This analysis does toward for four types of the human position postures because each posture has different value of specific absorption rate (SAR) based on the size of the mesh cells of the design. Based on two designs of the human body, the lowest of the mesh cells value will reduce time to simulate SAR. For each posture has different value of SAR for each part of the human body because the whole human body has different types of tissues. Therefore, the CST studio software uses extremely to simulate the SAR value toward human position posture due to high power transmission line.
Physica A: Statistical Mechanics and its Applications, 2017
Recent neurophysiological experiments suggest that populations of neurons use a computational sch... more Recent neurophysiological experiments suggest that populations of neurons use a computational scheme in which spike timing is regulated by common non-Gaussian inputs across neurons. The presence of beyond-pairwise correlations in the neuronal inputs and the spiking outputs following a non-Gaussian statistics elicits the need of developing a new theoretical framework taking into account the complexity of synchronous activity patterns. To this end, we quantify the amount of higher-order correlations in the common neuronal inputs and outputs of a population of neurons. We provide a novel formalism, of easy numerical implementation, that can capture the subtle changes of the inputs heterogeneities. Within our approach, correlations across neurons arise from q-Gaussian inputs into threshold neurons and higherorder correlations in the spiking outputs activity are quantified by the parameter q. We present an exhaustive analysis of how input statistics are transformed in this threshold process into output statistics, and we show under which conditions higherorder correlations can lead to either bigger or smaller number of synchronized spikes in the neural population outputs.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2015
The phenomenon of synchronization between two or more areas of the brain coupled asymmetrically i... more The phenomenon of synchronization between two or more areas of the brain coupled asymmetrically is a relevant issue for understanding mechanisms and functions within the cerebral cortex. Anticipated synchronization (AS) refers to the situation in which the receiver system synchronizes to the future dynamics of the sender system while the intuitively expected delayed synchronization (DS) represents exactly the opposite case. AS and DS are investigated in the context of causal information formalism. More specifically, we use a multi-scale symbolic information-theory approach for discriminating the time delay displayed between two areas of the brain when they exchange information.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2015
Neurons tend to fire a spike when they are near a bifurcation from the resting state to spiking a... more Neurons tend to fire a spike when they are near a bifurcation from the resting state to spiking activity. It is a delicate balance between noise, dynamic currents and initial condition that determines the phase diagram of neural activity. Many possible ionic mechanisms can be accounted for as the source of spike generation. Moreover, the biophysics and the dynamics behind it can usually be described through a phase diagram that involves membrane voltage versus the activation variable of the ionic channel. In this paper, we present a novel methodology to characterize the dynamics of this system, which takes into account the fine temporal ‘structures’ of the complex neuronal signals. This allows us to accurately distinguish the most fundamental properties of neurophysiological neurons that were previously described by Izhikevich considering the phase-space trajectory, using a time causal space: statistical complexity versus Fisher information versus Shannon entropy.
When inhibitory neurons constitute about 40% of neurons they could have an important antinocicept... more When inhibitory neurons constitute about 40% of neurons they could have an important antinociceptive role, as they would easily regulate the level of activity of other neurons. We consider a simple network of cortical spiking neurons with axonal conduction delays and spike timing dependent plasticity, representative of a cortical column or hypercolumn with large proportion of inhibitory neurons. Each neuron fires following a Hodgkin-Huxley like dynamics and it is interconnected randomly to other neurons. The network dynamics is investigated estimating Bandt and Pompe probability distribution function associated to the interspike intervals and taking different degrees of inter-connectivity across neurons. More specifically we take into account the fine temporal "structures" of the complex neuronal signals not just by using the probability distributions associated to the inter spike intervals, but instead considering much more subtle measures accounting for their causal information: the Shannon permutation entropy, Fisher permutation information and permutation statistical complexity. This allows us to investigate how the information of the system might saturate to a finite value as the degree of inter-connectivity across neurons grows, inferring the emergent dynamical properties of the system.
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Papers by Fernando Montani