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  • 1
    Online-Ressource
    Online-Ressource
    IOP Publishing ; 2022
    In:  Journal of Neural Engineering Vol. 19, No. 2 ( 2022-04-01), p. 026003-
    In: Journal of Neural Engineering, IOP Publishing, Vol. 19, No. 2 ( 2022-04-01), p. 026003-
    Kurzfassung: Objective . Metal implants impact the dosimetry assessment in electrical stimulation techniques. Therefore, they need to be included in numerical models. While currents in the body are ionic, metals only allow electron transport. In fact, charge transfer between tissues and metals requires electric fields to drive electrochemical reactions at the interface. Thus, metal implants may act as insulators or as conductors depending on the scenario. The aim of this paper is to provide a theoretical argument that guides the choice of the correct representation of metal implants in electrical models while considering the electrochemical nature of the problem Approach. We built a simple model of a metal implant exposed to a homogeneous electric field of various magnitudes. The same geometry was solved using two different models: a purely electric one (with different conductivities for the implant), and an electrochemical one. As an example of application, we also modeled a transcranial electrical stimulation (tES) treatment in a realistic head model with a skull plate using a high and low conductivity value for the plate. Main results . Metal implants generally act as electric insulators when exposed to electric fields up to around 100 V m −1 and they only resemble a perfect conductor for fields in the order of 1000 V m −1 and above. The results are independent of the implant’s metal, but they depend on its geometry. tES modeling with implants incorrectly treated as conductors can lead to errors of 50% or more in the estimation of the induced fields Significance. Metal implants can be accurately represented by a simple electrical model of constant conductivity, but an incorrect model choice can lead to large errors in the dosimetry assessment. Our results can be used to guide the selection of the most appropriate model in each scenario.
    Materialart: Online-Ressource
    ISSN: 1741-2560 , 1741-2552
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2022
    ZDB Id: 2135187-9
    SSG: 12
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Online-Ressource
    Online-Ressource
    IOP Publishing ; 2023
    In:  Journal of Neural Engineering Vol. 20, No. 2 ( 2023-04-01), p. 026004-
    In: Journal of Neural Engineering, IOP Publishing, Vol. 20, No. 2 ( 2023-04-01), p. 026004-
    Kurzfassung: Objective. We provide a systematic framework for quantifying the effect of externally applied weak electric fields on realistic neuron compartment models as captured by physiologically relevant quantities such as the membrane potential or transmembrane current as a function of the orientation of the field. Approach. We define a response function as the steady-state change of the membrane potential induced by a canonical external field of 1 V m −1 as a function of its orientation. We estimate the function values through simulations employing reconstructions of the rat somatosensory cortex from the Blue Brain Project. The response of different cell types is simulated using the NEURON simulation environment. We represent and analyze the angular response as an expansion in spherical harmonics. Main results. We report membrane perturbation values comparable to those in the literature, extend them to different cell types, and provide their profiles as spherical harmonic coefficients. We show that at rest, responses are dominated by their dipole terms ( ℓ = 1 ), in agreement with experimental findings and compartment theory. Indeed, we show analytically that for a passive cell, only the dipole term is nonzero. However, while minor, other terms are relevant for states different from resting. In particular, we show how ℓ = 0 and ℓ = 2 terms can modify the function to induce asymmetries in the response. Significance. This work provides a practical framework for the representation of the effects of weak electric fields on different neuron types and their main regions—an important milestone for developing micro- and mesoscale models and optimizing brain stimulation solutions.
    Materialart: Online-Ressource
    ISSN: 1741-2560 , 1741-2552
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2023
    ZDB Id: 2135187-9
    SSG: 12
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    In: Journal of Neural Engineering, IOP Publishing, Vol. 19, No. 5 ( 2022-10-01), p. 055005-
    Kurzfassung: Objective. In partial epilepsies, interictal epileptiform discharges (IEDs) are paroxysmal events observed in epileptogenic zone (EZ) and non-epileptogenic zone (NEZ). IEDs’ generation and recurrence are subject to different hypotheses: they appear through glutamatergic and gamma-aminobutyric acidergic (GABAergic) processes; they may trigger seizures or prevent seizure propagation. This paper focuses on a specific class of IEDs, spike-waves (SWs), characterized by a short-duration spike followed by a longer duration wave, both of the same polarity. Signal analysis and neurophysiological mathematical models are used to interpret puzzling IED generation. Approach. Interictal activity was recorded by intracranial stereo-electroencephalography (SEEG) electrodes in five different patients. SEEG experts identified the epileptic and non-epileptic zones in which IEDs were detected. After quantifying spatial and temporal features of the detected IEDs, the most significant features for classifying epileptic and non-epileptic zones were determined. A neurophysiologically-plausible mathematical model was then introduced to simulate the IEDs and understand the underlying differences observed in epileptic and non-epileptic zone IEDs. Main results. Two classes of SWs were identified according to subtle differences in morphology and timing of the spike and wave component. Results showed that type-1 SWs were generated in epileptogenic regions also involved at seizure onset, while type-2 SWs were produced in the propagation or non-involved areas. The modeling study indicated that synaptic kinetics, cortical organization, and network interactions determined the morphology of the simulated SEEG signals. Modeling results suggested that the IED morphologies were linked to the degree of preserved inhibition. Significance. This work contributes to the understanding of different mechanisms generating IEDs in epileptic networks. The combination of signal analysis and computational models provides an efficient framework for exploring IEDs in partial epilepsies and classifying EZ and NEZ.
    Materialart: Online-Ressource
    ISSN: 1741-2560 , 1741-2552
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2022
    ZDB Id: 2135187-9
    SSG: 12
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    In: Journal of Neural Engineering, IOP Publishing, Vol. 19, No. 5 ( 2022-10-01), p. 055002-
    Kurzfassung: Work in the last two decades has shown that neural mass models (NMM) can realistically reproduce and explain epileptic seizure transitions as recorded by electrophysiological methods (EEG, SEEG). In previous work, advances were achieved by increasing excitation and heuristically varying network inhibitory coupling parameters in the models. Based on these early studies, we provide a laminar NMM capable of realistically reproducing the electrical activity recorded by SEEG in the epileptogenic zone during interictal to ictal states. With the exception of the external noise input into the pyramidal cell population, the model dynamics are autonomous. By setting the system at a point close to bifurcation, seizure-like transitions are generated, including pre-ictal spikes, low voltage fast activity, and ictal rhythmic activity. A novel element in the model is a physiologically motivated algorithm for chloride dynamics: the gain of GABAergic post-synaptic potentials is modulated by the pathological accumulation of chloride in pyramidal cells due to high inhibitory input and/or dysfunctional chloride transport. In addition, in order to simulate SEEG signals for comparison with real seizure recordings, the NMM is embedded first in a layered model of the neocortex and then in a realistic physical model. We compare modeling results with data from four epilepsy patient cases. By including key pathophysiological mechanisms, the proposed framework captures succinctly the electrophysiological phenomenology observed in ictal states, paving the way for robust personalization methods based on NMMs.
    Materialart: Online-Ressource
    ISSN: 1741-2560 , 1741-2552
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2022
    ZDB Id: 2135187-9
    SSG: 12
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Online-Ressource
    Online-Ressource
    Frontiers Media SA ; 2010
    In:  Frontiers in Systems Neuroscience Vol. 4 ( 2010)
    In: Frontiers in Systems Neuroscience, Frontiers Media SA, Vol. 4 ( 2010)
    Materialart: Online-Ressource
    ISSN: 1662-5137
    Sprache: Unbekannt
    Verlag: Frontiers Media SA
    Publikationsdatum: 2010
    ZDB Id: 2453005-0
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Online-Ressource
    Online-Ressource
    Institute of Electrical and Electronics Engineers (IEEE) ; 2017
    In:  IEEE Transactions on Biomedical Engineering Vol. 64, No. 9 ( 2017-9), p. 2230-2240
    In: IEEE Transactions on Biomedical Engineering, Institute of Electrical and Electronics Engineers (IEEE), Vol. 64, No. 9 ( 2017-9), p. 2230-2240
    Materialart: Online-Ressource
    ISSN: 0018-9294 , 1558-2531
    RVK:
    Sprache: Unbekannt
    Verlag: Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2017
    ZDB Id: 2021742-0
    ZDB Id: 2571926-9
    ZDB Id: 2561637-7
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Online-Ressource
    Online-Ressource
    Institute of Electrical and Electronics Engineers (IEEE) ; 2019
    In:  IEEE Transactions on Biomedical Engineering Vol. 66, No. 6 ( 2019-6), p. 1695-1704
    In: IEEE Transactions on Biomedical Engineering, Institute of Electrical and Electronics Engineers (IEEE), Vol. 66, No. 6 ( 2019-6), p. 1695-1704
    Materialart: Online-Ressource
    ISSN: 0018-9294 , 1558-2531
    RVK:
    Sprache: Unbekannt
    Verlag: Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2019
    ZDB Id: 2021742-0
    ZDB Id: 2571926-9
    ZDB Id: 2561637-7
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    In: Biomedical Physics & Engineering Express, IOP Publishing, Vol. 9, No. 4 ( 2023-07-01), p. 045022-
    Kurzfassung: Intracranial electrodes are used clinically for diagnostic or therapeutic purposes, notably in drug-refractory epilepsy (DRE) among others. Visualization and quantification of the energy delivered through such electrodes is key to understanding how the resulting electric fields modulate neuronal excitability, i.e. the ratio between excitation and inhibition. Quantifying the electric field induced by electrical stimulation in a patient-specific manner is challenging, because these electric fields depend on a number of factors: electrode trajectory with respect to folded brain anatomy, biophysical (electrical conductivity / permittivity) properties of brain tissue and stimulation parameters such as electrode contacts position and intensity. Here, we aimed to evaluate various biophysical models for characterizing the electric fields induced by electrical stimulation in DRE patients undergoing stereoelectroencephalography (SEEG) recordings in the context of pre-surgical evaluation. This stimulation was performed with multiple-contact intracranial electrodes used in routine clinical practice. We introduced realistic 3D models of electrode geometry and trajectory in the neocortex. For the electrodes, we compared point (0D) and line (1D) sources approximations. For brain tissue, we considered three configurations of increasing complexity: a 6-layer spherical model, a toy model with a sulcus representation, replicating results from previous approaches; and went beyond the state-of-the-art by using a realistic head model geometry. Electrode geometry influenced the electric field distribution at close distances (∼3 mm) from the electrode axis. For larger distances, the volume conductor geometry and electrical conductivity dominated electric field distribution. These results are the first step towards accurate and computationally tractable patient-specific models of electric fields induced by neuromodulation and neurostimulation procedures.
    Materialart: Online-Ressource
    ISSN: 2057-1976
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2023
    ZDB Id: 2844309-3
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 9
    In: Journal of Neural Engineering, IOP Publishing, Vol. 20, No. 1 ( 2023-02-01), p. 016005-
    Kurzfassung: Objective. Stereotactic-electroencephalography (SEEG) and scalp EEG recordings can be modeled using mesoscale neural mass population models (NMMs). However, the relationship between those mathematical models and the physics of the measurements is unclear. In addition, it is challenging to represent SEEG data by combining NMMs and volume conductor models due to the intermediate spatial scale represented by these measurements. Approach. We provide a framework combining the multi-compartmental modeling formalism and a detailed geometrical model to simulate the transmembrane currents that appear in layer 3, 5 and 6 pyramidal cells due to a synaptic input. With this approach, it is possible to realistically simulate the current source density (CSD) depth profile inside a cortical patch due to inputs localized into a single cortical layer and the induced voltage measured by two SEEG contacts using a volume conductor model. Based on this approach, we built a framework to connect the activity of a NMM with a volume conductor model and we simulated an example of SEEG signal as a proof of concept. Main results. CSD depends strongly on the distribution of the synaptic inputs onto the different cortical layers and the equivalent current dipole strengths display substantial differences (of up to a factor of four in magnitude in our example). Thus, the inputs coming from different neural populations do not contribute equally to the electrophysiological recordings. A direct consequence of this is that the raw output of NMMs is not a good proxy for electrical recordings. We also show that the simplest CSD model that can accurately reproduce SEEG measurements can be constructed from discrete monopolar sources (one per cortical layer). Significance. Our results highlight the importance of including a physical model in NMMs to represent measurements. We provide a framework connecting microscale neuron models with the neural mass formalism and with physical models of the measurement process that can improve the accuracy of predicted electrophysiological recordings.
    Materialart: Online-Ressource
    ISSN: 1741-2560 , 1741-2552
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2023
    ZDB Id: 2135187-9
    SSG: 12
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 10
    In: Frontiers in Neuroscience, Frontiers Media SA, Vol. 16 ( 2022-8-25)
    Kurzfassung: Transcranial electrical current stimulation (tES or tCS, as it is sometimes referred to) has been proposed as non-invasive therapy for pharmacoresistant epilepsy. This technique, which includes direct current (tDCS) and alternating current (tACS) stimulation involves the application of weak currents across the cortex to change cortical excitability. Although clinical trials have demonstrated the therapeutic efficacy of tES, its specific effects on epileptic brain activity are poorly understood. We sought to summarize the clinical and fundamental effects underlying the application of tES in epilepsy. Methods A systematic review was performed in accordance with the PRISMA guidelines. A database search was performed in PUBMED, MEDLINE, Web of Science and Cochrane CENTRAL for articles corresponding to the keywords “ epilepsy AND (transcranial current stimulation OR transcranial electrical stimulation) ”. Results A total of 56 studies were included in this review. Through these records, we show that tDCS and tACS epileptic patients are safe and clinically relevant techniques for epilepsy. Recent articles reported changes of functional connectivity in epileptic patients after tDCS. We argue that tDCS may act by affecting brain networks, rather than simply modifying local activity in the targeted area. To explain the mechanisms of tES, various cellular effects have been identified. Among them, reduced cell loss, mossy fiber sprouting, and hippocampal BDNF protein levels. Brain modeling and human studies highlight the influence of individual brain anatomy and physiology on the electric field distribution. Computational models may optimize the stimulation parameters and bring new therapeutic perspectives. Conclusion Both tDCS and tACS are promising techniques for epilepsy patients. Although the clinical effects of tDCS have been repeatedly assessed, only one clinical trial has involved a consistent number of epileptic patients and little knowledge is present about the clinical outcome of tACS. To fill this gap, multicenter studies on tES in epileptic patients are needed involving novel methods such as personalized stimulation protocols based on computational modeling. Furthermore, there is a need for more in vivo studies replicating the tES parameters applied in patients. Finally, there is a lack of clinical studies investigating changes in intracranial epileptiform discharges during tES application, which could clarify the nature of tES-related local and network dynamics in epilepsy.
    Materialart: Online-Ressource
    ISSN: 1662-453X
    Sprache: Unbekannt
    Verlag: Frontiers Media SA
    Publikationsdatum: 2022
    ZDB Id: 2411902-7
    Standort Signatur Einschränkungen Verfügbarkeit
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