Effects of cavities on EEG dipole localization and their relations with surface electrode positions

Effects of cavities in the human head on EEG dipole localization have been investigated by computer simulation. The human head is represented by a homogeneous spherical conductor including an eccentric spherical cavity which approximates effects of actual cavities inside the head. The homogeneous sphere model is used for assessing the effects caused by neglecting the cavity in the volume conductor model in the inverse dipole fitting procedure. Four electrode configurations have been examined to investigate their relation to the EEG inverse dipole solution. After examination of 2520 dipoles in the brain, the effects of cavities in the human head are found to be negligible when the dipole is located in the cortex or in the subcortex. When the dipole is located in the brain stem, the EEG inverse dipole solution is strongly affected by the cavity and is sensitive to the electrode configuration on the scalp. The EEG inverse dipole solution in the deep brain is sensitive to inhomogeneity in the lower part of the head when a single positive or negative potential pole is observed by the electrodes on the scalp, and at the same time is sensitive to the extent of the scalp covered by the electrodes. In conclusion, the electrodes should cover as much of the upper scalp as possible for deep source localization.     

Effects of attachment position and shoulder orientation during calibration on the accuracy of the acromial tracker

The acromial tracker is used to measure scapular rotations during dynamic movements. The method has low accuracy in high elevations and is sensitive to its attachment location on the acromion. The aim of this study was to investigate the effect of the attachment position and shoulder orientation during calibration on the tracker accuracy. The tracker was attached to one of three positions: near the anterior edge of the acromion process, just above the acromial angle and the meeting point between the acromion and the scapular spine. The scapula locator was used to track the scapula during bilateral abduction simultaneously. The locator was used to calibrate the tracker at: no abduction, 30°, 60°, 90° and 120° humerothoracic abduction. ANOVA tests compared RMS errors for different attachment positions and calibration angles. The results showed that attaching the device at the meeting point between the acromion and the scapular spine gave the smallest errors and it was best to calibrate the device at 60° for elevations ≤90°, at 120° for elevations >90° and at 90°or 120° for the full range of abduction. The accuracy of the tracker is significantly improved if attached appropriately and calibrated for the range of movement being measured.     

Application of boundary element method for more accurate localization of EEG dipole sources

The proposed modification of boundary element method (BEM) makes it possible to solve direct EEG problem taking into account individual head geometry. This modification decreases computational cost thus enabling practical usage of BEM for localization of EEG dipole sources. The method developed was applied for error estimation of dipole localization using spherical approximation with the aid of BESA software. It was shown that the localization error of BESA for real head geometry could reach 2 cm.     

Blind source separation,wavelet denoising and discriminant analysis for EEG artefacts and noise cancelling

This paper proposes an automatic method for artefact removal and noise elimination from scalp electroencephalogram recordings (EEG). The method is based on blind source separation (BSS) and supervised classification and proposes a combination of classical and news features and classes to improve artefact elimination (ocular, high frequency muscle and ECG artefacts). The role of a supplementary step of wavelet denoising (WD) is explored and the interactions between BSS, denoising and classification are analyzed. The results are validated on simulated signals by quantitative evaluation criteria and on real EEG by medical expertise. The proposed methodology successfully rejected a good percentage of artefacts and noise, while preserving almost all the cerebral activity. The “denoised artefact-free” EEG presents a very good improvement compared with recorded raw EEG: 96% of the EEGs are easier to interpret.     

Resting-state EEG source localization and functional connectivity in schizophrenia-like psychosis of epilepsy

Background

It is unclear whether, like in schizophrenia, psychosis-related disruption in connectivity between certain regions, as an index of intrinsic functional disintegration, occurs in schizophrenia-like psychosis of epilepsy (SLPE). In this study, we sought to determine abnormal patterns of resting-state EEG oscillations and functional connectivity in patients with SLPE, compared with nonpsychotic epilepsy patients, and to assess correlations with psychopathological deficits.

Methodology/Principal Findings

Resting EEG was recorded in 21 patients with focal epilepsy and SLPE and in 21 clinically-matched non-psychotic epilepsy controls. Source current density and functional connectivity were determined using eLORETA software. For connectivity analysis, a novel nonlinear connectivity measure called “lagged phase synchronization” was used. We found increased theta oscillations in regions involved in the default mode network (DMN), namely the medial and lateral parietal cortex bilaterally in the psychotic patients relative to their nonpsychotic counterparts. In addition, patients with psychosis had increased beta temporo-prefrontal connectivity in the hemisphere with predominant seizure focus. This functional connectivity in temporo-prefrontal circuits correlated with positive symptoms. Additionally, there was increased interhemispheric phase synchronization between the auditory cortex of the affected temporal lobe and the Broca''s area correlating with auditory hallucination scores.

Conclusions/Significance

In addition to dysfunction of parietal regions that are part of the DMN, resting-state disrupted connectivity of the medial temporal cortex with prefrontal areas that are either involved in the DMN or implicated in psychopathological dysfunction may be critical to schizophrenia-like psychosis, especially in individuals with temporal lobe epilepsy. This suggests that DMN deficits might be a core neurobiological feature of the disorder, and that abnormalities in theta oscillations and beta phase synchronization represent the underlying neural activity.     

EEG source localization: comparative study of classical and neural network methods.

We address the problem of estimating biopotential sources within the brain, based on EEG signals observed on the scalp. This problem, known as the inverse problem of electrophysiology, has no closed-form solution, and requires iterative techniques such as the Levenberg-Marquardt (LM) algorithm. Considering the nonlinear nature of the inverse problem, and the low signal to noise ratio inherent in EEG signals, a backpropagation neural network (BPN) has been recently proposed as a solution. The technique has not been properly compared with classical techniques such as the LM method, or with more recent neural network techniques such as the Radial Basis Function (RBF) network. In this paper, we provide improved strategies based on BPN and consider RBF networks in solving the inverse problem. We compare the performances of BPN, RBF and a hybrid technique with that of the classical LM method.     

The effects of orientation, temperature, and displacement magnitude changes on the sonometrics system accuracy

The accuracy and reliability of a sonomicrometry system (Sonometrics Corporation, Ontario, Canada) was evaluated for its potential use in measuring 3-D in vivo joint kinematics. Distances between different sets of piezoelectric crystals were measured through a salt solution using ultrasound technology. We evaluated crystal-to-crystal distance under simulated in vivo conditions of changing crystal orientation and displacement magnitude. Crystal-to-crystal distance was also evaluated under changing solution temperature, since the crystals may be used at different temperatures. The 2 mm round and peg crystals were accurate to within 0.5mm for 0 through 180 degrees rotations, but the 2mm round suture loop crystals were only reliable at 0 degrees rotation. The speed of sound through a salt solution (and hence the distance between crystals) versus temperature was fit using a second order polynomial, C=1421.1+3.9808T-3.09x10(-2)T2, with an R2 value of 0.9998. The translational error was less than 0.072 mm for crystal displacements of 0.012, 0.2, 1.0, and 5.0 mm. The system was also accurate under dynamic conditions with translational errors that were less than 0.045 mm under 0.65 Hz motion. These results suggest that the Sonometrics crystals possess attributes (translational accuracy and rotational independence) that could provide the basis for a system capable of measuring joint kinematics.     

Effects of genotype, light regime, explant position and orientation on direct somatic embryogenesis from leaf explants of Phalaenopsis orchids

The influence of light regime, explant position and orientation on direct embryo formation from leaf explants of two Phalaenopsis, P. amabilis and P. Nebula, were investigated to optimize the protocol for regenerating of this orchid. When explants were cultured in light, direct embryogenesis was retarded in both species. Embryos showed whitish to pale green in color and larger size than those cultured in darkness. Furthermore, light regime induced explant browning, embryo necrosis and eventually low plantlet conversion rate. Sixty days of culture in darkness is the most suitable duration for direct embryo induction. Explant orientation also significantly affected direct embryo formation, and explants placed adaxial-side-up on culture medium had higher embryogenic response than abaxial-side-up orientation. In both species, the cut end had highest embryogenic competence than other parts of the explant. Moreover, when the leaf explant was cut transversely into two segments, the leaf basal segment had higher embryogenic competence than the leaf tip segment.     

Single molecule fluorescence image patterns linked to dipole orientation and axial position: application to myosin cross-bridges in muscle fibers

Background

Photoactivatable fluorescent probes developed specifically for single molecule detection extend advantages of single molecule imaging to high probe density regions of cells and tissues. They perform in the native biomolecule environment and have been used to detect both probe position and orientation.

Methods and Findings

Fluorescence emission from a single photoactivated probe captured in an oil immersion, high numerical aperture objective, produces a spatial pattern on the detector that is a linear combination of 6 independent and distinct spatial basis patterns with weighting coefficients specifying emission dipole orientation. Basis patterns are tabulated for single photoactivated probes labeling myosin cross-bridges in a permeabilized muscle fiber undergoing total internal reflection illumination. Emitter proximity to the glass/aqueous interface at the coverslip implies the dipole near-field and dipole power normalization are significant affecters of the basis patterns. Other characteristics of the basis patterns are contributed by field polarization rotation with transmission through the microscope optics and refraction by the filter set. Pattern recognition utilized the generalized linear model, maximum likelihood fitting, for Poisson distributed uncertainties. This fitting method is more appropriate for treating low signal level photon counting data than χ² minimization.

Conclusions

Results indicate that emission dipole orientation is measurable from the intensity image except for the ambiguity under dipole inversion. The advantage over an alternative method comparing two measured polarized emission intensities using an analyzing polarizer is that information in the intensity spatial distribution provides more constraints on fitted parameters and a single image provides all the information needed. Axial distance dependence in the emission pattern is also exploited to measure relative probe position near focus. Single molecule images from axial scanning fitted simultaneously boost orientation and axial resolution in simulation.     

Effect of the orientation of dipole fragments of the phospholipid molecule on the bilayer structure

By the method of minimization of phospholipid bilayers free energy it was shown that at a decrease of inclination angle of dipole fragments of phospholipid molecules to the bilayer surface there take place: a) an increase of bilayer density, b) a decrease of bilayer thickness caused by a decrease of dipole repulsive forces, c) an increase of the number of molecules in the bilayer due to hydrophobization of the latter. The existence of upper and lower critical angles of dipoles inclination to the bilayer surface were found: theta upcrit, theta lowcrit, if theta greater than or equal to the layers must be destroyed, and if theta less than or equal to theta lowcrit, transition of bilayers to the crystalline state must take place.     

Investigations on spectra and orientation of dipole moments of uracil and thymine by electrochromism

The direction of the ground stale dipole moment with respect to the transition moment to the lowest excited singlet state as well as the dipole moment in this excited state could be determined from the influence of an electric field on the light absorption of uracil and thymine in solution. By making use of results on the orientation of the transition moment in the molecular framework, the orientation of the ground-and excited-state dipole moments can also be fixed and compared with theoretical predictions. The agreement is fair. The measurements show that in both compounds a weak band is hidden under the longest-wavelength absorption band.     

Topography, independent component analysis and dipole source analysis of movement related potentials

The objective of this study was to test, in single subjects, the hypothesis that the signs of voluntary movement-related neural activity would first appear in the prefrontal region, then move to both the medial frontal and posterior parietal regions, progress to the medial primary motor area, lateralize to the contralateral primary motor area and finally involve the cerebellum (where feedback-initiated error signals are computed). Six subjects performed voluntary finger movements while DC coupled EEG was recorded from 64 scalp electrodes. Event-related potentials (ERPs) averaged on the movements were analysed both before and after independent component analysis (ICA) combined with dipole source analysis (DSA) of the independent components. Both a simple topographic analysis of undecomposed ERPs and the ICA/DSA analysis suggested that the original hypothesis was inadequate. The major departure from its predictions was that, while activity over many brain regions did appear at the expected times, it also appeared at unexpected times. Overall, the results suggest that the neuroscientific ‘standard model’, in which neural activity occurs sequentially in a series of discrete local areas each specialized for a particular function, may reflect the true situation less well than models in which large areas of brain shift simultaneously into and out of common activity states. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Maurer's clefts-restricted localization, orientation and export of a Plasmodium falciparum RIFIN

RIFINs are clonally variant antigens expressed in Plasmodium falciparum. Transfection and the green fluorescence protein (GFP) tagged either internally or C-terminally to the 3D7 PFI0050c RIFIN gene product were used to investigate protein localization, orientation and trafficking. Green fluorescence pattern emerging from live transfectant parasites expressing each of the RIFIN-GFP chimera was different. The internally GFP-tagged protein was exported to Maurer's clefts (MC) in the erythrocyte cytosol, whereas the C-terminally GFP-tagged full-length RIFIN chimera was not trafficked out of the parasite. Interestingly, when some RIFIN-specific C-terminal amino acid sequences were removed, the resulting truncated molecule reached the MC. Using anti-RIFIN and anti-GFP antibodies to probe both live and fixed transfectants, staining was confined to MC and was not detected on the erythrocyte surface, a location previously suggested for this protein family. From selective permeabilization experiments, the highly variable portion of the RIFIN-GFP-insertion chimera appeared to be exposed to the erythrocyte cytosol, presumably anchored in the MC membrane via the two transmembrane domains. Trafficking of both chimeras in young ring stages was sensitive to Brefeldin A (BFA), although older rings showed differential sensitivity to BFA.     

Influence of head models on EEG simulations and inverse source localizations

Background  

The structure of the anatomical surfaces, e.g., CSF and gray and white matter, could severely influence the flow of volume currents in a head model. This, in turn, will also influence the scalp potentials and the inverse source localizations. This was examined in detail with four different human head models.     

脑电磁场及脑内源定位的研究进展

本文从物理学的电磁场理论阐述脑电磁场的产生原理;从源的等效偶极子定位和皮层成像方法两个方面回顾了脑内源定位的研究进展;作为脑电的基础性研究,它对临床医学的发展具有积极的推动作用。     

Effects of ambient noise on detectability and localization of avian songs and tones by observers in grasslands

Probability of detection and accuracy of distance estimates in aural avian surveys may be affected by the presence of anthropogenic noise, and this may lead to inaccurate evaluations of the effects of noisy infrastructure on wildlife. We used arrays of speakers broadcasting recordings of grassland bird songs and pure tones to assess the probability of detection, and localization accuracy, by observers at sites with and without noisy oil and gas infrastructure in south‐central Alberta from 2012 to 2014. Probability of detection varied with species and with speaker distance from transect line, but there were few effects of noisy infrastructure. Accuracy of distance estimates for songs and tones decreased as distance to observer increased, and distance estimation error was higher for tones at sites with infrastructure noise. Our results suggest that quiet to moderately loud anthropogenic noise may not mask detection of bird songs; however, errors in distance estimates during aural surveys may lead to inaccurate estimates of avian densities calculated using distance sampling. We recommend caution when applying distance sampling if most birds are unseen, and where ambient noise varies among treatments.