Restoring the encoding properties of a stochastic neuron model by an exogenous noise

Here we evaluate the possibility of improving the encoding properties of an impaired neuronal system by superimposing an exogenous noise to an external electric stimulation signal. The approach is based on the use of mathematical neuron models consisting of stochastic HH-like circuit, where the impairment of the endogenous presynaptic inputs is described as a subthreshold injected current and the exogenous stimulation signal is a sinusoidal voltage perturbation across the membrane. Our results indicate that a correlated Gaussian noise, added to the sinusoidal signal can significantly increase the encoding properties of the impaired system, through the Stochastic Resonance (SR) phenomenon. These results suggest that an exogenous noise, suitably tailored, could improve the efficacy of those stimulation techniques used in neuronal systems, where the presynaptic sensory neurons are impaired and have to be artificially bypassed

A computational model for real-time calculation of electric field due to transcranial magnetic stimulation in clinics

The aim of this paper is to propose an approach for an accurate and fast (real-time) computation of the electric field induced inside the whole brain volume during a transcranial magnetic stimulation (TMS) procedure. The numerical solution implements the admittance method for a discretized realistic brain model derived from Magnetic Resonance Imaging (MRI). Results are in a good agreement with those obtained using commercial codes and require much less computational time. An integration of the developed codewith neuronavigation toolswill permit real-time evaluation of the stimulated brain regions during the TMSdelivery, thus improving the efficacy of clinical applications

Vliv stochastického chování iontových kanálů na přenos signálu a informace na excitabilních neuronálních membránách

Stochastické chování napěťově řízených iontových kanálů způsobuje fluktuace v konduktanci a napětí na neuronálních membránách, čímž přispívá k všudypřítomnému šumu v nervové soustavě. Přestože se tento fenomén vyskytuje i na jiných částech neuronu, zde jsme se soustředili pouze na axon a na způsob, jakým neuronální šum ovlivňuje axonální vstupně-výstupní charakteristiky. Problematika byla analyzována za použití nového výpočetního kompartmentálního modelu, který jsme naprogramovali v prostředí Matlab, a který je založený na matematickém Hodgkin-Huxley formalismu s kanálovým šumem implementovaným pomocí rozšířené metody Markovových řetězců Monte Carlo. Model byl důkladně ověřen k tomu, aby věrně simuloval savčí axon CA3 neuronu. Na základě našich simulací jsme kvantitativně potvrdili dosavadní poznatek, že neuronální šum je výraznější na membránách s nižším počtem Na+ a K+ kanálů, a že výrazně zvyšuje variabilitu doby propagace akčního potenciálu (AP) podél axonu, čímž i snižuje časovou preciznost AP. Simulace analyzující efekt demyelinizace axonu a axonálního průměru korelovala s dřívějšími poznatky zmíněnými v Literatuře. Dále jsme se soustředili na vzorce akčních potenciálů a jak je jejich propagace ovlivněna intervaly mezi nimi (ISI, inter-spike intervals). Zjistili jsme, že AP vypálené s krátkými...The stochastic behavior of voltage-gated ion channels causes fluctuations of conductances and voltages across neuronal membranes, contributing to the neuronal noise which is ubiquitous in the nervous system. While this phenomenon can be observed also on other parts of the neuron, here we concentrated on the axon and the way the channel noise influences axonal input-output characteristics. This was analysed by working with our newly created computational compartmental model, programmed in Matlab environment, built up using the Hodgkin-Huxley mathematical formalism and channel noise implemented via extended Markov Chain Monte Carlo method. The model was thoroughly verified to simulate plausibly a mammalian axon of CA3 neuron. Based on our simulations, we confirmed quantitatively the findings that the channel noise is the most prominent on membranes with smaller number of Na+ and K+ channels and that it majorly increases the variability of travel times of action potentials (APs) along axons, decreasing thereby the temporal precision of APs. The simulations analysing the effect of axonal demyelination and axonal diameter correlated well with other finding referred in Literature. We further focused on spike pattern and how is its propagation influenced by inter-spike intervals (ISI). We found, that APs fired...Department of PhysiologyKatedra fyziologieFaculty of SciencePřírodovědecká fakult

Restoring the encoding properties of a stochastic neuron model by an exogenous noise

Here we evaluate the possibility of improving the encoding properties of an impaired neuronal system by superimposing an exogenous noise to an external electric stimulation signal. The approach is based on the use of mathematical neuron models consisting of stochastic HH-like circuit, where the impairment of the endogenous presynaptic inputs is described as a subthreshold injected current and the exogenous stimulation signal is a sinusoidal voltage perturbation across the membrane. Our results indicate that a correlated Gaussian noise, added to the sinusoidal signal can significantly increase the encoding properties of the impaired system, through the Stochastic Resonance (SR) phenomenon. These results suggest that an exogenous noise, suitably tailored, could improve the efficacy of those stimulation techniques used in neuronal systems, where the presynaptic sensory neurons are impaired and have to be artificially bypassed

Stochastic Resonance as a tool to optimize Perceptual Learning in neurovisual rehabilitation: An exploratory study

openLa ricerca pilota descritta in questo elaborato mirava ad esplorare il fenomeno controintuitivo del miglioramento percettivo indotto dal rumore nella percezione visiva umana. Questo fenomeno, noto come Risonanza Stocastica, potrebbe risultare particolarmente utile per ottimizzare il Perceptual Learning visivo, su cui si basano diversi protocolli di riabilitazione visiva. L’obiettivo principale di questa ricerca era pertanto la produzione di un’ulteriore evidenza della SR nella percezione visiva umana, e in particolare in un compito utilizzato da un protocollo di riabilitazione visiva chiamato Neural Restoration Therapy. A questo scopo, sono stati condotti tre studi comportamentali con partecipanti normo-vedenti in cui sono stati manipolati i livelli di intensità di rumore visivo casuale, aggiunto agli stimoli visivi, in un compito di discriminazione temporale (2-IFC) di stimoli Gabor Patches. Il primo studio comprendeva 10 condizioni diverse tra loro per intensità di rumore aggiunto agli stimoli, proporzionale al valore di luminanza di ogni pixel dello stimolo. Nel secondo e nel terzo studio il rumore era aggiunto in maniera casuale al 50% dei pixel del riquadro di presentazione degli stimoli, per un totale di 6 condizioni e 5 condizioni, rispettivamente. I risultati dei tre studi hanno mostrato nessun fenomeno di risonanza stocastica. In particolare, nello studio 1 il rumore non aveva alcun effetto sulla prestazione, mentre vi era un effetto della posizione dello stimolo. Nello studio 2 la prestazione era inversamente proporzionale ai livelli di rumore, mentre nello studio 3 non è stato osservato nessun effetto del rumore. Complessivamente, questi risultati suggeriscono che il metodo psicofisico adattivo delle staircase impiegato dal protocollo NRT non porta alla manifestazione della SR. Pertanto, questo fenomeno psicofisico potrebbe non essere utilizzabile nei protocolli riabilitativi visivi basati sul Perceptual Learning.The pilot study described in this paper aimed to explore the counterintuitive phenomenon of perceptual improvement induced by noise in human visual perception. This phenomenon, known as Stochastic Resonance (SR), could prove to be particularly useful for optimizing visual perceptual learning, which forms the basis of various visual rehabilitation protocols. The main objective of this research was to provide further evidence of SR in human visual perception, particularly in a task used by a visual rehabilitation protocol called Neural Restoration Therapy (NRT). To achieve this goal, three behavioral studies were conducted with normally sighted participants in which the levels of random visual noise added to visual stimuli were manipulated in a two-interval forced-choice (2-IFC) task involving Gabor Patches stimuli. The first study included 10 different conditions varying in the intensity of noise added to the stimuli, proportional to the luminance value of each pixel in the stimulus. In the second and third studies, noise was randomly added to 50% of the pixels in the stimulus presentation frame, resulting in a total of 6 and 5 conditions, respectively. The results of the three studies showed no Stochastic Resonance phenomenon. Specifically, in Study 1, noise had no effect on performance, while there was an effect of stimulus location. In Study 2, performance was inversely proportional to noise levels, while in Study 3, no noise effect was observed. Overall, these results suggest that the adaptive psychophysical method used by the NRT protocol, employing staircases, does not lead to the manifestation of SR. Therefore, this psychophysical phenomenon may not be applicable in visual rehabilitation protocols based on Perceptual Learning