The Experts below are selected from a list of 3879 Experts worldwide ranked by ideXlab platform
Arden V. Nelson - One of the best experts on this subject based on the ideXlab platform.
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A visual study of Surface potentials and Laplacians due to distributed neocortical sources: computer simulations and evoked potentials.
Brain topography, 1991Co-Authors: Paul L. Nunez, Kenneth L. Pilgreen, Andrew F. Westdorp, S.k. Law, Arden V. NelsonAbstract:A "picture book" of Surface potentials, Laplacians, and magnetic fields due to distributed, neocortical sources is presented. The mathematically simulated data is based on 4200 current sources at the macrocolumn scale. Estimated Scalp Surface maps are based on the three-concentic spheres model of the head. Emphasis is placed on the effects of sampling with a limited number of electrodes, the choice of reference electrode, and the use of the spline Laplacian to improve spatial resolution. The spline Laplacian is applied to median and ulnar nerve somatosensory evoked potentials and to auditory evoked potentials including P300. Substantial improvement in spatial resolution over conventional methods is obtained. The implementation of practical high resolution EEG systems based on the spline Laplacian is considered.
Craig E. Tenke - One of the best experts on this subject based on the ideXlab platform.
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issues and considerations for using the Scalp Surface laplacian in eeg erp research a tutorial review
International Journal of Psychophysiology, 2015Co-Authors: Jürgen Kayser, Craig E. TenkeAbstract:Despite the recognition that the Surface Laplacian may counteract adverse effects of volume conduction and recording reference for Surface potential data, electrophysiology as a discipline has been reluctant to embrace this approach for data analysis. The reasons for such hesitation are manifold but often involve unfamiliarity with the nature of the underlying transformation, as well as intimidation by a perceived mathematical complexity, and concerns of signal loss, dense electrode array requirements, or susceptibility to noise. We revisit the pitfalls arising from volume conduction and the mandated arbitrary choice of EEG reference, describe the basic principle of the Surface Laplacian transform in an intuitive fashion, and exemplify the differences between common reference schemes (nose, linked mastoids, average) and the Surface Laplacian for frequently-measured EEG spectra (theta, alpha) and standard event-related potential (ERP) components, such as N1 or P3. We specifically review common reservations against the universal use of the Surface Laplacian, which can be effectively addressed by employing spherical spline interpolations with an appropriate selection of the spline flexibility parameter and regularization constant. We argue from a pragmatic perspective that not only are these reservations unfounded but that the continued predominant use of Surface potentials poses a considerable impediment on the progress of EEG and ERP research.
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Issues and considerations for using the Scalp Surface Laplacian in EEG/ERP research: A tutorial review.
International journal of psychophysiology : official journal of the International Organization of Psychophysiology, 2015Co-Authors: Jürgen Kayser, Craig E. TenkeAbstract:Despite the recognition that the Surface Laplacian may counteract adverse effects of volume conduction and recording reference for Surface potential data, electrophysiology as a discipline has been reluctant to embrace this approach for data analysis. The reasons for such hesitation are manifold but often involve unfamiliarity with the nature of the underlying transformation, as well as intimidation by a perceived mathematical complexity, and concerns of signal loss, dense electrode array requirements, or susceptibility to noise. We revisit the pitfalls arising from volume conduction and the mandated arbitrary choice of EEG reference, describe the basic principle of the Surface Laplacian transform in an intuitive fashion, and exemplify the differences between common reference schemes (nose, linked mastoids, average) and the Surface Laplacian for frequently-measured EEG spectra (theta, alpha) and standard event-related potential (ERP) components, such as N1 or P3. We specifically review common reservations against the universal use of the Surface Laplacian, which can be effectively addressed by employing spherical spline interpolations with an appropriate selection of the spline flexibility parameter and regularization constant. We argue from a pragmatic perspective that not only are these reservations unfounded but that the continued predominant use of Surface potentials poses a considerable impediment on the progress of EEG and ERP research.
Lionel Breton - One of the best experts on this subject based on the ideXlab platform.
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Exploration of Scalp Surface lipids reveals squalene peroxide as a potential actor in dandruff condition
Archives of Dermatological Research, 2016Co-Authors: Roland Jourdain, Alain Moga, Philippe Vingler, Charles El Rawadi, Florence Pouradier, Luc Souverain, Philippe Bastien, Nicolas Amalric, Lionel BretonAbstract:Dandruff is a common but complex disorder with three major contributing factors: (1) individual predisposition, (2) Scalp sebum and (3) Malassezia yeast colonization. To obtain further insights into the role of sebum in dandruff biogenesis, we analyzed Scalp lipid species in a cohort of ten dandruff-free (control) and ten dandruff-afflicted volunteers by gas chromatography coupled to mass spectrometry. Lipid peroxidation levels and biochemical markers of oxidative stress were also assessed. Squalene, a major sebum component, was significantly more peroxidized in dandruff-affected Scalps, resulting in significantly higher ratios of squalene monohydroperoxide (SQOOH)/squalene. This was observed when comparing dandruff-affected zones of dandruff subjects to both their non-affected zones and control subjects. In addition, other biomarkers such as malondialdehyde indicated that oxidative stress levels were raised on dandruff Scalps. Surprisingly, differences regarding either free or bound fatty acids were fairly rare and minor. Certain novel findings, especially squalene peroxidation levels, were then confirmed in a validation cohort of 24 dandruff-affected subjects, by comparing dandruff-affected and non-dandruff zones from the same individuals. As SQOOH can induce both keratinocyte inflammatory responses and hyperproliferation in vitro, we hypothesized that increased SQOOH could be considered as a new etiological dandruff factor via its ability to impair Scalp barrier function. Our results also indicated that Malassezia could be a major source of squalene peroxidation on the Scalp.
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dandruff is associated with disequilibrium in the proportion of the major bacterial and fungal populations colonizing the Scalp
PLOS ONE, 2013Co-Authors: Cecile Clavaud, Roland Jourdain, Charles El Rawadi, Florence Pouradier, Avner Barhen, Magali Tichit, Christiane Bouchier, Jacques Guillot, Florence Menardszczebara, Lionel BretonAbstract:The bacterial and fungal communities associated with dandruff were investigated using culture-independent methodologies in the French subjects. The major bacterial and fungal species inhabiting the Scalp subject’s were identified by cloning and sequencing of the conserved ribosomal unit regions (16S for bacterial and 28S-ITS for fungal) and were further quantified by quantitative PCR. The two main bacterial species found on the Scalp Surface were Propionibacterium acnes and Staphylococcus epidermidis, while Malassezia restricta was the main fungal inhabitant. Dandruff was correlated with a higher incidence of M. restricta and S. epidermidis and a lower incidence of P. acnes compared to the control population (p<0.05). These results suggested for the first time using molecular methods, that dandruff is linked to the balance between bacteria and fungi of the host Scalp Surface.
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Dandruff Is Associated with Disequilibrium in the Proportion of the Major Bacterial and Fungal Populations Colonizing the Scalp
PLoS ONE, 2013Co-Authors: Cecile Clavaud, Roland Jourdain, Charles El Rawadi, Florence Pouradier, Magali Tichit, Christiane Bouchier, Jacques Guillot, Avner Bar-hen, Florence Ménard-szczebara, Lionel BretonAbstract:The bacterial and fungal communities associated with dandruff were investigated using culture-independent methodologies in the French subjects. The major bacterial and fungal species inhabiting the Scalp subject's were identified by cloning and sequencing of the conserved ribosomal unit regions (16S for bacterial and 28S-ITS for fungal) and were further quantified by quantitative PCR. The two main bacterial species found on the Scalp Surface were Propionibacterium acnes and Staphylococcus epidermidis, while Malassezia restricta was the main fungal inhabitant. Dandruff was correlated with a higher incidence of M. restricta and S. epidermidis and a lower incidence of P. acnes compared to the control population (p
Bruce Tromberg - One of the best experts on this subject based on the ideXlab platform.
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an indwelling brachytherapy balloon catheter potential use as an intracranial light applicator for photodynamic therapy
Journal of Neuro-oncology, 1999Co-Authors: Henry Hirschberg, Knut Lote, Tuan Pham, Steen J Madsen, Bruce TrombergAbstract:An indwelling balloon applicator developed for postoperative intracavity afterloading brachytherapy was evaluated for photodynamic therapy (PDT). Following tumor resection, the applicator is positioned in the center of the resultant cavity and the balloon is inflated with a scattering solution. The liquid-filled balloon stabilizes the resection cavity ensuring a constant and simple geometric shape during treatment. The catheter is brought out through the skin and adjusted so that 1–2 cm projects above the Scalp Surface.
Paul L. Nunez - One of the best experts on this subject based on the ideXlab platform.
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A visual study of Surface potentials and Laplacians due to distributed neocortical sources: computer simulations and evoked potentials.
Brain topography, 1991Co-Authors: Paul L. Nunez, Kenneth L. Pilgreen, Andrew F. Westdorp, S.k. Law, Arden V. NelsonAbstract:A "picture book" of Surface potentials, Laplacians, and magnetic fields due to distributed, neocortical sources is presented. The mathematically simulated data is based on 4200 current sources at the macrocolumn scale. Estimated Scalp Surface maps are based on the three-concentic spheres model of the head. Emphasis is placed on the effects of sampling with a limited number of electrodes, the choice of reference electrode, and the use of the spline Laplacian to improve spatial resolution. The spline Laplacian is applied to median and ulnar nerve somatosensory evoked potentials and to auditory evoked potentials including P300. Substantial improvement in spatial resolution over conventional methods is obtained. The implementation of practical high resolution EEG systems based on the spline Laplacian is considered.
