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Lagarde S, Modolo J, Yochum M, Carvallo A, Ballabeni A, Scavarda D, Carron R, Villeneuve N, Bartolomei F, Wendling F. Modification of brain conductivity in human focal epilepsy: A model-based estimation from stereoelectroencephalography. Epilepsia 2024; 65:1744-1755. [PMID: 38491955 DOI: 10.1111/epi.17957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 03/04/2024] [Accepted: 03/05/2024] [Indexed: 03/18/2024]
Abstract
OBJECTIVE We have developed a novel method for estimating brain tissue electrical conductivity using low-intensity pulse stereoelectroencephalography (SEEG) stimulation coupled with biophysical modeling. We evaluated the hypothesis that brain conductivity is correlated with the degree of epileptogenicity in patients with drug-resistant focal epilepsy. METHODS We used bipolar low-intensity biphasic pulse stimulation (.2 mA) followed by a postprocessing pipeline for estimating brain conductivity. This processing is based on biophysical modeling of the electrical potential induced in brain tissue between the stimulated contacts in response to pulse stimulation. We estimated the degree of epileptogenicity using a semi-automatic method quantifying the dynamic of fast discharge at seizure onset: the epileptogenicity index (EI). We also investigated how the location of stimulation within specific anatomical brain regions or within lesional tissue impacts brain conductivity. RESULTS We performed 1034 stimulations of 511 bipolar channels in 16 patients. We found that brain conductivity was lower in the epileptogenic zone (EZ; unpaired median difference = .064, p < .001) and inversely correlated with the epileptogenic index value (p < .001, Spearman rho = -.32). Conductivity values were also influenced by anatomical site, location within lesion, and delay between SEEG electrode implantation and stimulation, and had significant interpatient variability. Mixed model multivariate analysis showed that conductivity is significantly associated with EI (F = 13.45, p < .001), anatomical regions (F = 5.586, p < .001), delay since implantation (F = 14.71, p = .003), and age at SEEG (F = 6.591, p = .027), but not with the type of lesion (F = .372, p = .773) or the delay since last seizure (F = 1.592, p = .235). SIGNIFICANCE We provide a novel model-based method for estimating brain conductivity from SEEG low-intensity pulse stimulations. The brain tissue conductivity is lower in EZ as compared to non-EZ. Conductivity also varies significantly across anatomical brain regions. Involved pathophysiological processes may include changes in the extracellular space (especially volume or tortuosity) in epileptic tissue.
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Affiliation(s)
- Stanislas Lagarde
- Epileptology and Cerebral Rhythmology Department (member of the ERN EpiCARE Network), APHM, Timone Hospital, Marseille, France
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
- University Hospitals (HUG) and University of Geneva (UNIGE), Geneva, Switzerland
| | - Julien Modolo
- LTSI - U1099, University of Rennes, INSERM, Rennes, France
| | - Maxime Yochum
- LTSI - U1099, University of Rennes, INSERM, Rennes, France
| | | | - Alice Ballabeni
- Epileptology and Cerebral Rhythmology Department (member of the ERN EpiCARE Network), APHM, Timone Hospital, Marseille, France
- University of Modena and Reggio-Emilia, Modena, Italy
| | - Didier Scavarda
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
- Pediatric Neurosurgery Department, APHM, Timone Hospital, Marseille, France
| | - Romain Carron
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
- Stereotactic and Functional Neurosurgery Department, APHM, Timone Hospital, Marseille, France
| | | | - Fabrice Bartolomei
- Epileptology and Cerebral Rhythmology Department (member of the ERN EpiCARE Network), APHM, Timone Hospital, Marseille, France
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
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Popa RC, Serban CA, Barborica A, Zagrean AM, Buiu O, Dumbravescu N, Paslaru AC, Obreja C, Pachiu C, Stoian M, Marculescu C, Radoi A, Vulpe S, Ion M. Functional Enhancement and Characterization of an Electrophysiological Mapping Electrode Probe with Carbonic, Directional Macrocontacts. SENSORS (BASEL, SWITZERLAND) 2023; 23:7497. [PMID: 37687953 PMCID: PMC10490806 DOI: 10.3390/s23177497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 08/16/2023] [Accepted: 08/21/2023] [Indexed: 09/10/2023]
Abstract
Electrophysiological mapping (EM) using acute electrode probes is a common procedure performed during functional neurosurgery. Due to their constructive specificities, the EM probes are lagging in innovative enhancements. This work addressed complementing a clinically employed EM probe with carbonic and circumferentially segmented macrocontacts that are operable both for neurophysiological sensing ("recording") of local field potentials (LFP) and for test stimulation. This paper illustrates in-depth the development that is based on the direct writing of functional materials. The unconventional fabrication processes were optimized on planar geometry and then transferred to the cylindrically thin probe body. We report and discuss the constructive concept and architecture of the probe, characteristics of the electrochemical interface deduced from voltammetry and chronopotentiometry, and the results of in vitro and in vivo recording and pulse stimulation tests. Two- and three-directional macrocontacts were added on probes having shanks of 550 and 770 μm diameters and 10-23 cm lengths. The graphitic material presents a ~2.7 V wide, almost symmetric water electrolysis window, and an ultra-capacitive charge transfer. When tested with clinically relevant 150 μs biphasic current pulses, the interfacial polarization stayed safely away from the water window for pulse amplitudes up to 9 mA (135 μC/cm2). The in vivo experiments on adult rat models confirmed the high-quality sensing of LFPs. Additionally, the in vivo-prevailing increase in the electrode impedance and overpotential are discussed and modeled by an ionic mobility-reducing spongiform structure; this restricted diffusion model gives new applicative insight into the in vivo-uprisen stimulation overpotential.
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Affiliation(s)
- Radu C. Popa
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Cosmin-Andrei Serban
- Termobit Prod Srl, 020281 Bucharest, Romania; (C.-A.S.); (A.B.)
- Fhc, Inc., Bowdoin, ME 04287, USA
- Faculty of Physics, University of Bucharest, 077125 Magurele, Romania
| | - Andrei Barborica
- Termobit Prod Srl, 020281 Bucharest, Romania; (C.-A.S.); (A.B.)
- Fhc, Inc., Bowdoin, ME 04287, USA
- Faculty of Physics, University of Bucharest, 077125 Magurele, Romania
| | - Ana-Maria Zagrean
- Physiology and Neuroscience Department, “Carol Davila” University of Medicine and Pharmacy, 050474 Bucharest, Romania; (A.-M.Z.); (A.-C.P.)
| | - Octavian Buiu
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Niculae Dumbravescu
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Alexandru-Catalin Paslaru
- Physiology and Neuroscience Department, “Carol Davila” University of Medicine and Pharmacy, 050474 Bucharest, Romania; (A.-M.Z.); (A.-C.P.)
| | - Cosmin Obreja
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Cristina Pachiu
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Marius Stoian
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Catalin Marculescu
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Antonio Radoi
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Silviu Vulpe
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
| | - Marian Ion
- National Institute for R&D in Microtechnologies–IMT Bucharest, 077190 Bucharest, Romania; (O.B.); (N.D.); (C.O.); (C.P.); (M.S.); (C.M.); (A.R.); (S.V.); (M.I.)
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Emin D, Fallah A, Salamon N, Mathern G, Akhtari M. Distinctive ionic transport of freshly excised human epileptogenic brain tissue. APPLIED PHYSICS LETTERS 2021; 119:253701. [PMID: 34966188 PMCID: PMC8691960 DOI: 10.1063/5.0077825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2021] [Accepted: 12/02/2021] [Indexed: 06/14/2023]
Abstract
Epileptogenic lesions have higher concentrations of sodium than does normal brain tissue. Such lesions are palpably recognized by a surgeon and then excised in order to eliminate epileptic seizures with their associated abnormal electrical behavior. Here, we study the frequency-dependent electrical conductivities of lesion-laden tissues excised from the brains of epilepsy patients. The low-frequency (<1000 Hz) conductivity of biological tissue primarily probes extracellular solvated sodium-cations traveling parallel to membranes within regions bounded by blockages. This conductivity rises monotonically toward saturation as the frequency surpasses the rate with which diffusing solvated sodium cations encounter blockages. We find that saturation occurs at dramatically higher frequencies in excised brain tissue containing epileptogenic lesions than it does in normal brain tissue. By contrast, such an effect is not reported for tumors embedded in other excised biological tissue. All told, epileptogenic lesions generate frequency-dependent conductivities that differ qualitatively from those of both normal brain tissues and tumors.
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Affiliation(s)
- David Emin
- Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA
| | - Aria Fallah
- Department of Neurosurgery and Pediatrics, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Noriko Salamon
- Department of Radiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Gary Mathern
- Department of Neurosurgery and Pediatrics, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Massoud Akhtari
- Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
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Emin D, Fallah A, Salamon N, Yong W, Frew A, Mathern G, Akhtari M. Understanding the sodium cation conductivity of human epileptic brain tissue. AIP ADVANCES 2021; 11:045118. [PMID: 33907630 PMCID: PMC8053039 DOI: 10.1063/5.0041906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Accepted: 04/02/2021] [Indexed: 06/12/2023]
Abstract
Transient and frequency-dependent conductivity measurements on excised brain-tissue lesions from epilepsy patients indicate that sodium cations are the predominant charge carriers. The transient conductivity ultimately vanishes as ions encounter blockages. The initial and final values of the transient conductivity correspond to the high-frequency and low-frequency limits of the frequency-dependent conductivity, respectively. Carrier dynamics determines the conductivity between these limits. Typically, the conductivity rises monotonically with increasing frequency. By contrast, when pathology examinations found exceptionally disorganized excised tissue, the conductivity falls with increasing frequency as it approaches its high-frequency limit. To analyze these measurements, excised tissues are modeled as mixtures of "normal" tissue within which sodium cations can diffuse and "abnormal" tissue within which sodium cations are trapped. The decrease in the conductivity with increasing frequency indicates the predominance of trapping. The high-frequency conductivity decreases as the rate with which carriers are liberated from traps decreases. A relatively low conductivity results when most sodium cations remain trapped in "abnormal" brain tissue, while few move within "normal" brain tissue. Thus, the high densities of sodium nuclei observed by 23Na-MRI in epilepsy patients' lesions are consistent with the low densities of diffusing sodium cations inferred from conductivity measurements of excised lesions.
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Affiliation(s)
- David Emin
- Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA
| | - Aria Fallah
- Departments of Neurosurgery and Pediatrics, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Noriko Salamon
- Department of Radiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - William Yong
- Department of Pathology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Andrew Frew
- Human Brain Mapping Center, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Gary Mathern
- Departments of Neurosurgery and Pediatrics, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
| | - Massoud Akhtari
- Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
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Carvallo A, Modolo J, Benquet P, Lagarde S, Bartolomei F, Wendling F. Biophysical Modeling for Brain Tissue Conductivity Estimation Using SEEG Electrodes. IEEE Trans Biomed Eng 2019; 66:1695-1704. [DOI: 10.1109/tbme.2018.2877931] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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