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  • 1
    ISSN: 1469-8986
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Various studies have indicated an impairment of sensory signal processing in schizophrenic patients. Anatomical and functional imaging studies have indicated morphological and metabolic abnormalities in the thalamus in schizophrenia. Other results give evidence for an additional role of cortical dysfunction in sensory processing in schizophrenia. Advanced analysis of human median nerve somatosensory evoked potentials (SEPs) reveals a brief oscillatory burst of low-amplitude and high-frequency activity (∼600 Hz), the so-called high frequency oscillations (HFOs). The present study explores the behavior of HFOs in a cohort of schizophrenic patients in comparison to a group of controls. HFOs in the group of patients appeared with a delayed latency. In the low-frequency part of the SEPs an increase in amplitude was found. These results are interpreted to reflect a lack of somatosensory inhibition in the somatosensory pathway, either at a thalamic or a cortical level.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-6792
    Keywords: Head modelling ; Source localization ; Early SEPs, 3D-MR-tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Source localizations of early somatosensory evoked potentials and electrical potentials produced by dipoles in the region of the central sulcus were computed using realistically shaped boundary-element head models (BEM) and compared to localizations obtained using 3-shell spherical models. Realistically shaped 3-shell boundary-element-models were constructed on the basis of the individual anatomy obtained from 3D-MR-tomography in 6 subjects. Spherical head models were fitted to the actual locations of the electrodes and to the surface of the heads, respectively. Source locations calculated within the spherical head models differed by an average of 4 mm (range: 2 to 7 mm) with respect to the 3-shell BEM, taking into account the limited accuracy of this model. This mislocation was most prominently due to deeper source locations predicted using a spherical head model and caused by incorrect modelling of the geometry of the heads, although sources were located in a favourable region of the heads.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-6792
    Keywords: Source localization ; Current density reconstruction ; Boundary-element-method ; Finite-element-method ; Temporal lobe epilepsy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract During the last decade multiple work has been done to determine the sources of epileptiform activity by means of dipole source localization based on recordings of the magnetoencephalogram (MEG) or the electroencephalogram (EEG). The actual available advanced volume conductor models and the multiple source reconstruction by regularization may give new impulse to EEG based source analyses in epilepsy patients. This study demonstrates the principal properties of these techniques. We applied two different EEG source reconstruction techniques within different volume conductor models to localize induced spike activity in a selected patient suffering from medically intractable temporal lobe epilepsy: 1) single moving dipole solution in a 3-shell spherical model versus individual head models (boundary-element-model, BEM, and finite-element-model, FEM); 2) a regularization technique for current density reconstructions using both BEM and FEM. When compared to findings of invasive recordings no adequate source locations were derived from the moving dipole solution in both the 3-shell head model and BEM. In contrast, a high congruence of source reconstruction and invasive determination of the focus was obtained using the regularization techniques in both BEM and FEM, indicating the high spatial accuracy of this technique in individual head models.
    Type of Medium: Electronic Resource
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