Spatio-temporal source localization and Granger causality in ictal source analysis

We have proposed a new ictal source analysis approach by combining a spatio-temporal source localization approach, and causal interaction estimation technique. The FINE approach is used to identify neural electrical sources from spatio-temporal scalp-EEGs. The Granger causality estimation uses source waveforms estimated by FINE to characterize the causal interaction between the neural electrical sources in order to distinguish primary sources, which initiate ictal events, from secondary sources, which are caused by propagation. In the present study, we applied the proposed analysis approach to an epilepsy patient with symptomatic MRI lesions. It is found that the primary ictal source is within the visible lesion, which gave the consistent presurgical evaluation as MRI for this patient.

Orientational distributions and nematic order of rodlike magnetic nanoparticles in dispersions

Using small-angle neutron scattering (SANS), we have investigated the orientational order of iron nanoparticles dispersed in cyclohexanone. The particles have rodlike shape and size distributions with an average length of 200 nm and an average diameter of 25 nm. SANS shows an anisotropy, which is a measure of orientational order, in magnetic dispersions with a volume fraction of 3.2% and 3.9% iron particles in shear flow and/or magnetic field. The scattering anisotropy can be fitted by a model assuming an Onsager distribution of the orientation of the particles in shear flow. The orientational distribution of particles oriented by a magnetic field can be described by a different model assuming the Maier-Saupe orientational distribution for uniaxial ferromagnetic particles. The orientational distribution parameter m for the Maier-Saupe distribution or alpha for the Onsager distribution and the orientational order parameter S have been determined at shear rates gamma[over ] of to 0-4000 s(-1) and in magnetic fields of 0-18 mT. The S values indicate that the particles start to orient either in a shear flow of 100 s(-1) or in a magnetic field of 6 mT. Applying only shear results in an orientational order, with the dispersion returning to the disordered state when the shear rate is decreased to zero. In sharp contrast, application of magnetic fields greater than 6 mT results in orientational order in the field-increasing cycle, and two-thirds of the orientational order remains when the field is decreased to zero. This shows that the order in a magnetic field is different from the order in a shear flow, the action of magnetizing the particles along a certain direction is irreversible, and the orientational order parameter exhibits hysteresis.

A neural network model for monotone linear asymmetric variational inequalities

Linear variational inequality is a uniform approach for some important problems in optimization and equilibrium problems. In this paper, we give a neural-network model for solving asymmetric linear variational inequalities. The model is based on a simple projection and contraction method. Computer simulation is performed for linear programming (LP) and linear complementarity problems (LCP). The test results for LP problem demonstrate that our model converges significantly faster than the three existing neural-network models examined in a recent comparative study paper.

Analysis of single nucleotide polymorphisms in the melanocortin-4 receptor promoter in infantile spasms

OBJECTIVES

Infantile spasms is a severe epileptic encephalopathy of infancy. ACTH that ameliorates infantile spasms might act through activating the central melanocortin-4 receptor (MC4R) to suppress excessive production of corticotrophin-releasing hormone (CRH). This study aimed to elucidate an association between the genetic variants of the MC4R gene and infantile spasms.

METHODS

The study population comprised 96 patients with infantile spasms and 118 controls. All subjects were screened for variations in the promoter and coding region of the MC4R gene using a direct sequencing method. ATCH responses in patients carrying different genotypes were also assessed.

RESULTS

The distributions of genotypes and alleles of rs11872992 in the MC4R promoter were significantly different between cases and controls. The frequencies of heterozygous carriers (TC genotype) were significantly lower in cases (10%) than in controls (27%) (p=0.003). The distributions of rs11872992 TC and CC genotypes were significantly different between ACTH responders and non-responders (OR, 0.14; 95% C.I, 0.03-0.69; p=0.007). The T-allele carriers (83.3%) had a higher responsiveness to ACTH than non-carriers (41.7%).

CONCLUSIONS

The present study shows that genetic variants in the MC4R promoter are associated with the development of infantile spasms. The rs11872992 polymorphism influences ACTH treatment responses in patients with infantile spasms.

Imaging functional brain connectivity patterns from high-resolution EEG and fMRI via graph theory

We describe a set of computational tools able to estimate cortical activity and connectivity from high-resolution EEG and fMRI recordings in humans. These methods comprise the estimation of cortical activity using realistic geometry head volume conductor models and distributed cortical source models, followed by the evaluation of cortical connectivity between regions of interest coincident with the Brodmann areas via the use of Partial Directed Coherence. Connectivity patterns estimated on the cortical surface in different frequency bands are then imaged and interpreted with measures based on graph theory. These computational tools were applied on a set of EEG and fMRI data from a Stroop task to demonstrate the potential of the proposed approach. The present findings suggest that the methodology is able to identify differences in functional connectivity patterns elicited by different experimental tasks or conditions.

Three-dimensional ventricular activation imaging by means of equivalent current source modeling and estimation

This paper presents a novel electrocardiographic inverse approach for imaging the 3-D ventricular activation sequence based on the modeling and estimation of the equivalent current density throughout the entire myocardial volume. The spatio-temporal coherence of the ventricular excitation process is utilized to derive the activation time from the estimated time course of the equivalent current density. At each time instant during the period of ventricular activation, the distributed equivalent current density is noninvasively estimated from body surface potential maps (BSPM) using a weighted minimum norm approach with a spatio-temporal regularization strategy based on the singular value decomposition of the BSPMs. The activation time at any given location within the ventricular myocardium is determined as the time point with the maximum local current density estimate. Computer simulation has been performed to evaluate the capability of this approach to image the 3-D ventricular activation sequence initiated from a single pacing site in a physiologically realistic cellular automaton heart model. The simulation results demonstrate that the simulated "true" activation sequence can be accurately reconstructed with an average correlation coefficient of 0.90, relative error of 0.19, and the origin of ventricular excitation can be localized with an average localization error of 5.5 mm for 12 different pacing sites distributed throughout the ventricles.

Menstrual-like changes in mice are provoked through the pharmacologic withdrawal of progesterone using mifepristone following induction of decidualization

BACKGROUND

Cyclic shedding of the endometrium is unique to menstruating species, and mouse menstruation models by physiologic progesterone withdrawal have been previously reported. Since progesterone action ablated pharmacologically may provide more insight into the mechanism of action, a mouse menstruation model using mifepristone was established.

METHODS

Mifepristone was administered following oil-induced decidualization in ovarectomized mice primed with hormones. Morphology, hormone levels, leukocytes and apoptosis were evaluated over a period of 48 h after treatment. Vaginal smears were used to monitor bleedings.

RESULTS

Mifepristone induced menstrual-like changes. Tissue breakdown was drastic by 16 h, and the decidual zone was shed by 24 h while the mice bled. The endometrium regenerated from 24 h onwards and became completely restored by 48 h. These results are consistent with previous reports. However, although progesterone levels remained constant, estradiol levels increased after the treatment. The CD45(+) cells showed two peaks of increase at 16 h (breakdown phase) and 32 h (regeneration phase) (Leukocyte levels also increased in the unstimulated horns, but no breakdown changes occurred there). Moreover, apoptosis drastically increased by 16 h concurrent with tissue destruction. These results differed from those of the physiologic withdrawal models.

CONCLUSIONS

The pharmacologic withdrawal of progesterone by mifepristone successfully provoked a menstrual-like process in mice after artificial decidualization.

Evidence of structural defect enhanced room-temperature ferromagnetism in Co-doped ZnO

We report experimentally that room-temperature ferromagnetism of Co-doped ZnO is strongly correlated with structural defects, and that carriers involved in carrier-mediated exchange are by nature by-products of the creation of the defects. On the other hand, the carrier concentration has pronounced influences on the absorption edge in optical transmission spectra of epitaxial Co:ZnO films, in which both a blue-shift and a red-shift are observed. Furthermore, high-temperature annealing results in evolution of the local Co structure from Co(2+) replacing Zn(2+) to a Co(3)O(4)-based phase, which most likely accounts for the transition from ferromagnetism to paramagnetism in the Co:ZnO films.

Improved estimation of human cortical activity and connectivity with the multimodal integration of neuroelectric and hemodynamic data

In the last decade, the possibility to noninvasively estimate cortical activity and connectivity has been highlighted by the application of the techniques known as high resolution EEG. These techniques include a subject's multi-compartment head model (scalp, skull, dura mater, cortex) constructed from individual magnetic resonance images, multi-dipole source model, and regularized linear inverse source estimates of cortical current density. More recently, it has proved as the use of information from the hemodynamic responses of the cortical areas as revealed by block-designed (strength of activated voxels) fMRI improves dramatically the estimates of cortical activity and connectivity. Here, we present some applications of such estimation in two set of high resolution EEG and fMRI data, related to the motor (finger tapping) and cognitive (Stroop) tasks. We observed that the proposed technology was able to unveil the direction of the information flow between the cortical regions of interest.

Motion analysis of right ventricular wall based on an electromechanical biventricular model

Based on our previously developed electrical heart model, an electromechanical biventricular model, which couples the electrical property and mechanical property of the heart, was constructed and the right ventricular wall motion and deformation was simulated using this model. The model was developed on the basis of composite material theory and finite element method. The excitation propagation was simulated by electrical heart model, and the resultant active forces were used to study the ventricular wall motion during systole. The simulation results show that: (1) The right ventricular free wall moves towards the septum, and at the same time, the base and middle of free wall move towards the apex, which reduce the volume of right ventricle; (2) The minimum principle strain (E3) is largest at the apex, then at the middle of free wall, and its direction is in the approximate direction of epicardial muscle fibers. These results are in good accordance with solutions obtained from MR tagging images. It suggests that such electromechanical biventricular model can be used to assess the mechanical function of two ventricles.

Time-varying cortical connectivity by high resolution EEG and directed transfer function: simulations and application to finger tapping data

The problem of the definition and evaluation of brain connectivity has become a central one in neuroscience during the latest years, as a way to understand the organization and interaction of cortical areas during the execution of cognitive or motor tasks. The method of the directed transfer function (DTF) is a frequency-domain approach to this problem, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. So far, all the connectivity estimations performed on cerebral electromagnetic signals were computed between signals gathered from the electric or magnetic sensors. However, the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites. In this paper we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. As main contributions of this work, we present the results of a wide simulation study, aiming to evaluate performances of DTF application on this kind of data, and a statistical analysis (via the ANOVA, analysis of variance) of the results obtained for different levels of signal to noise ratio and temporal length, as they have been systematically imposed on simulated signals. Finally, we provide an application to the estimation of cortical connectivity from high resolution EEG recordings related to finger tapping movements.

Motor imagery classification by means of source analysis methods

We report our investigation of classification of imagined left and right hand movements by applying source analysis methods. Independent component analysis (ICA) is used as a spatio-temporal filter, then equivalent dipole analysis and cortical current density imaging methods are applied to reconstruct equivalent sources, to aid classification of motor imagery tasks in a human subject. The classification was considered correct if the equivalent source was found over the motor cortex in the corresponding hemisphere. A classification rate of about 80% was achieved in the human subject studied using both the equivalent dipole analysis and the cortical current density imaging analysis.

Enhancement of classification accuracy of a time-frequency approach for an EEG-based brain-computer interface

OBJECTIVES

The aim of this paper is to develop a new algorithm to enhance the performance of EEG-based brain-computer interface (BCI).

METHODS

We improved our time-frequency approach of classification of motor imagery (MI) tasks for BCI applications. The approach consists of Laplacian filtering, band-pass filtering and classification by correlation of time-frequency-spatial patterns.

RESULTS AND CONCLUSIONS

Through off-line analysis of data collected during a "cursor control" experiment, we evaluated the capability of our new method to reveal major features of the EEG control for enhancement of MI classification accuracy. The pilot results in a human subject are promising, with an accuracy rate of 96.1%.

Wnt signaling in stem cells and lung cancer

The Wnt signal transduction pathway plays important roles during embryo development, regulating cell proliferation and survival of immature cells. However, its improper function can lead to harmful consequences for humans, such as aberrant cell proliferation and, therefore, cancer. Increasing evidence suggests that stem cells may be the source of mutant cells that cause cancers to develop and proliferate. Wnt signaling has been shown to promote self-renewal in both gut epithelial and hematopoietic stem cells (HSCs) and to trigger critical pathways in carcinogenesis. Although the function of stem cells in solid tumor development is unclear, the Wnt pathway's role in determining the fate and self-renewal potential of cancer stem cells suggests a critical role in carcinogenesis. The development of new inhibitors, such as antibodies or small molecules, to inhibit this pathway may be of great therapeutic utility against cancer.

Enhancement of Classification Accuracy of a Time-frequency Approach for an EEG-based Brain-computer Interface

Objectives : The aim of this paper is to develop a new algorithm to enhance the performance of EEG-based brain-computer interface (BCI).

Methods : We improved our time-frequency approach of classification of motor imagery (MI) tasks for BCI applications. The approach consists of Laplacian filtering, band-pass filtering and classification by correlation of time-frequency-spatial patterns.

Results and Conclusions : Through off-line analysis of data collected during a “cursor control" experiment, we evaluated the capability of our new method to reveal major features of the EEG control for enhancement of MI classification accuracy. The pilot results in a human subject are promising, with an accuracy rate of 96.1%.

Cortical dipole imaging of movement-related potentials by means of parametric inverse filters incorporating with signal and noise covariance

OBJECTIVE

The objective of this study is to explore suitable spatial filters for inverse estimation of cortical equivalent dipole layer imaging from the scalp electroencephalogram. We utilize cortical dipole source imaging to locate the possible generators of scalp-measured movement-related potentials (MRPs) in human.

METHODS

The effects of incorporating signal and noise covariance into inverse procedures were examined by computer simulations and experimental study. The parametric projection filter (PPF) and parametric Weiner filter (PWF) were applied to an inhomogeneous three-sphere head model under various noise conditions.

RESULTS

The present simulation results suggest that the PWF incorporating signal information provides better cortical dipole layer imaging results than the PPF and Tikhonov regularization under the condition of moderate and high correlation between signal and noise distributions. On the other hand, the PPF has better performance than other inverse filters under the condition of low correlation between signal and noise distributions. The proposed methods were applied to self-paced MRPs in order to identify the anatomic substrate locations of neural generators. The dipole layer distributions estimated by means of PPF are well-localized as compared with blurred scalp potential maps and dipole layer distribution estimated by Tikhonov regularization. The proposed methods demonstrated that the contralateral premotor cortex was preponderantly activated in relation to movement performance.

CONCLUSIONS

In cortical dipole source imaging, the PWF has better performance especially when the correlation between the signal and noise is high. The proposed inverse method was applicable to human experiments of MRPs if the signal and noise covariances were obtained.

Genome-wide scan for type 1 diabetic nephropathy in the Finnish population reveals suggestive linkage to a single locus on chromosome 3q

Diabetic nephropathy (DN) is the primary cause of morbidity and mortality in patients with type 1 as well as type 2 diabetes, and accounts for 40% of end-stage renal disease in the Western world. Familial clustering of DN suggests importance of genetic factors in the development of the disease. In the present study, we performed a two-stage genome-wide scan to search for chromosomal loci containing susceptibility genes for nephropathy in patients with type 1 diabetes. In total, 83 discordant sib pairs (DSPs), sibs concordant for type 1 diabetes but discordant for nephropathy, were collected from Finland, a homogeneous population with one of the highest incidences of type 1 diabetes. To map loci for DN, we applied DSP analysis to detect linkage. In the initial scan, 73 DSPs were typed using 900 markers with an average intermarker distance of approximately 4 cM. Multipoint DSP analysis identified five chromosome regions (3q, 4p, 9q, 16q, and 22p) with maximum logarithm of odds (LOD) score (MLS) >or=1.0 (corresponding to a nominal P-value <or=0.015). In the second stage, additional 43 markers flanking these five loci were genotyped in all 83 DSPs. Using simulations, we determined the empirical threshold with LOD score of 1.76 and 3.12 for suggestive and significant linkage, respectively. No locus reached the genome-wide significance of 5%. However, one locus on 3q reached suggestive linkage with MLS of 2.67 (P=4.4 x 10(-4)). These results, together with data from others, suggest that the locus on 3q most likely has a susceptibility gene for DN.

Three-Dimensional Microchannels in Biodegradable Polymeric Films for Control Orientation and Phenotype of Vascular Smooth Muscle Cells

The poor mechanical strength and vasoactivity of current small-diameter tissue engineered blood vessels (TEBVs) remain unsolved problems. Given the plasticity of smooth muscle cells (SMCs), 1 of the main limitations of current scaffolding techniques is the difficulty in controlling SMC phenotype shifts in vitro. A synthetic phenotype allows the cells to rapidly proliferate and produce extracellular matrix (ECM), whereas a shift to contractile phenotype with organized ECM ultimately provides a functional blood vessel. In this study, 3D deep (65 microm) and wide microchannels separated by high-aspect ratio (8) microwalls were successfully ultraviolet (UV) microembossed using a liquid UV polymerizable biodegradable macromer (poly(epsilon-caprolactone-r-L-lactide-r-glycolide) diacrylate) and the in vitro guidance effects of varying channel width (40-160 microm) on SMCs were verified. The results show that SMCs cultured in the wider microchannels (80-160 microm wide) switch from fibroblast morphology and random orientation to spindle-shaped morphology, and align along the direction of the microchannel nearing confluence achieved with similar cell density to unpatterned film. Further, an enhanced expression of smooth muscle alpha-actin of SMCs grown on micropatterns was found nearing confluence, which demonstrates a phenotype shift to a more contractile phenotype. These films are flexible and can be folded into tubular and lamellar structures for tissue engineering of small-diameter TEBVs as well as other organs such as esophagus or intestine. These results suggest that these micropatterned synthetic biodegradable scaffolds may be useful for guiding SMCs to grow into functional, small-diameter vascular grafts.

Effect of an increase in coronary perfusion on transmural ventricular repolarization

The effect of increased coronary flow on transmural ventricular repolarization was investigated in six pentobabital-anesthetized sheep. Fresh blood at 10 ml/min was injected into the left circumflex coronary artery (LCX) in addition to the normal coronary flow. Unipolar electrocardiograms were simultaneously registered from epicardium, mid-myocardium and endocardium with fine plunge needles. Activation-recovery interval (ARI) was measured from the unipolar electrocardiograms and was used for estimating the ventricular repolarization duration. It was found that intracoronary blood injection (n=3) prolonged ARI in the epicardium, mid-myocardium and endocardium by an average of 34 +/- 16, 28 +/- 18 and 25 +/- 13 ms, respectively (p<0.01). Pretreatment with nitro-L-arginine (n=3), a nitric synthase inhibitor, diminished the flow-induced ARI prolongation across the ventricular wall. In conclusion, an increase in coronary flow lengthens the duration of transmural ventricular repolarization. These effects appear to be mediated by nitric oxide from the coronary endothelium.

An osteopontin splice variant induces anchorage independence in human breast cancer cells

In malignant tumors, metastasis genes are typically deregulated by aberrant expression or splicing. Osteopontin is expressed at high levels by various cancers and contributes importantly to their invasive potential. In contrast, osteopontin derived from host cells induces cellular immunity and could bolster antitumor protection by cytotoxic T lymphocytes. Here we show that breast cancer cells express multiple splice variants of osteopontin. According to RT-PCR analysis of human breast tissue specimens, the splice variant osteopontin-c is a highly specific marker for transformed cells, which is not expressed in their surrounding normal tissue. The full-length form of osteopontin aggregates in the presence of physiologic amounts of calcium and, in this state, leads to enhanced cell adhesion. Ostensibly, this effect is inhibitory for tumor cell dissemination. The shortest splice variant, osteopontin-c, does not aggregate in the presence of calcium and enhances clone formation in soft agar. According to microarray analysis, osteopontin-c induces the expression of oxidoreductases, consistent with protection from anoikis during anchorage-independent growth. These studies define a third functional domain of osteopontin, beside the C-terminal CD44-binding site and the central integrin-binding site. They also provide evidence for a bifunctional character of osteopontin, with the soluble form supporting invasiveness and the aggregated form promoting adhesion.

Viruses, endoplasmic reticulum stress, and interferon responses

Viral infection induces endoplasmic reticulum (ER) stress and interferon responses. While viral double-stranded RNA intermediates trigger interferon responses, viral polypeptides synthesized during infection stimulate ER stress. Among the interferon-regulated gene products, the double-stranded RNA-dependent protein kinase (PKR) plays a key role in limiting viral replication. Thus, to establish productive infection, viruses have evolved mechanisms to overcome the deleterious effects of PKR. It has become clear that ER stress causes translational attenuation and transcriptional upregulation of genes encoding proteins that facilitate folding or degradation of proteins. Notably, prolonged ER stress triggers apoptosis. Therefore, viruses are confronted with the consequences of ER stress. Emerging evidence suggests that viruses not only interfere with the interferon system involving PKR but also manipulate the programs emanating from the ER in a complex way, which may facilitate viral replication or pathogenesis. This review highlights recent progress in these areas.

Imaging 3-dimensional cardiac electrical activity from intra-cavity potentials

We propose a novel approach to image 3- dimensional (3-D) cardiac electrical activity from intra-cavity electrical potentials. The 3-D cardiac electrical activity is estimated by minimizing the difference between the recorded and model-generated intra-cavity potential distributions. The feasibility of the proposed concept is tested by a computer simulation.

Ectopic galanin expression and normal galanin receptor 2 and galanin receptor 3 mRNA levels in the forebrain of galanin transgenic mice

The functional interactions of the neuropeptide galanin (GAL) occur through its binding to three G protein-coupled receptor subtypes: galanin receptor (GALR) 1, GALR2 and GALR3. Previously, we demonstrated that GALR1 mRNA expression was increased in the CA1 region of the hippocampus and discrete hypothalamic nuclei in galanin transgenic (GAL-tg) mice. This observation suggested a compensatory adjustment in cognate receptors in the face of chronic GAL exposure. To evaluate the molecular alterations to GALR2 and GALR3 in the forebrain of GAL overexpressing mice, we performed complementary quantitative, real-time PCR (qPCR), in situ hybridization, and immunohistochemistry in select forebrain regions of GAL-tg mice to characterize the neuronal distribution and magnitude of GAL mRNA and peptide expression and the consequences of genetically manipulating the neuropeptide GAL on the expression of GALR2 and GALR3 receptors. We found that GAL-tg mice displayed dramatic increases in GAL mRNA and peptide in the frontal cortex, posterior cortex, hippocampus, septal diagonal band complex, amygdala, piriform cortex, and olfactory bulb. Moreover, there was evidence for ectopic neuronal GAL expression in forebrain limbic regions that mediate cognitive and affective behaviors, including the piriform and entorhinal cortex and amygdala. Interestingly, regional qPCR analysis failed to reveal any changes in GALR2 or GALR3 expression in the GAL-tg mice, suggesting that, contrary to GALR1, these receptor genes are not under ligand-mediated regulatory control. The GAL-tg mouse model may provide a useful tool for the investigation of GAL ligand-receptor relationships and their role in normal cognitive and affective functions as well as in the onset of neurological disease.

Estimation of in vivo human brain-to-skull conductivity ratio from simultaneous extra- and intra-cranial electrical potential recordings

OBJECTIVE

The present study aims to accurately estimate the in vivo brain-to-skull conductivity ratio by means of cortical imaging technique. Simultaneous extra- and intra-cranial potential recordings induced by subdural current stimulation were analyzed to get the estimation.

METHODS

The effective brain-to-skull conductivity ratio was estimated in vivo for 5 epilepsy patients. The estimation was performed using multi-channel simultaneously recorded scalp and cortical electrical potentials during subdural electrical stimulation. The cortical imaging technique was used to compute the inverse cortical potential distribution from the scalp recorded potentials using a 3-shell head volume conductor model. The brain-to-skull conductivity ratio, which leads to the most consistent cortical potential estimates with respect to the direct intra-cranial measurements, is considered to be the effective brain-to-skull conductivity ratio.

RESULTS

The present estimation provided consistent results in 5 human subjects studied. The in vivo effective brain-to-skull conductivity ratio ranged from 18 to 34 in the 5 epilepsy patients.

CONCLUSIONS

The effective brain-to-skull conductivity ratio can be estimated from simultaneous intra- and extra-cranial potential recordings and the averaged value/standard deviation is 25+/-7.

SIGNIFICANCE

The present results provide important experimental data on the brain-to-skull conductivity ratio, which is of significance for accurate brain source localization using piece-wise homogeneous head models.

Estimation of the cortical functional connectivity with the multimodal integration of high-resolution EEG and fMRI data by directed transfer function

Nowadays, several types of brain imaging device are available to provide images of the functional activity of the cerebral cortex based on hemodynamic, metabolic, or electromagnetic measurements. However, static images of brain regions activated during particular tasks do not convey the information of how these regions communicate with each other. In this study, advanced methods for the estimation of cortical connectivity from combined high-resolution electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data are presented. These methods include a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from individual magnetic resonance images, multidipole source model, and regularized linear inverse source estimates of cortical current density. Determination of the priors in the resolution of the linear inverse problem was performed with the use of information from the hemodynamic responses of the cortical areas as revealed by block-designed (strength of activated voxels) fMRI. We estimate functional cortical connectivity by computing the directed transfer function (DTF) on the estimated cortical current density waveforms in regions of interest (ROIs) on the modeled cortical mantle. The proposed method was able to unveil the direction of the information flow between the cortical regions of interest, as it is directional in nature. Furthermore, this method allows to detect changes in the time course of information flow between cortical regions in different frequency bands. The reliability of these techniques was further demonstrated by elaboration of high-resolution EEG and fMRI signals collected during visually triggered finger movements in four healthy subjects. Connectivity patterns estimated for this task reveal an involvement of right parietal and bilateral premotor and prefrontal cortical areas. This cortical region involvement resembles that revealed in previous studies where visually triggered finger movements were analyzed with the use of separate EEG or fMRI measurements.

Assessing cortical functional connectivity by linear inverse estimation and directed transfer function: simulations and application to real data

OBJECTIVE

To test a technique called Directed Transfer Function (DTF) for the estimation of human cortical connectivity, by means of simulation study and human study, using high resolution EEG recordings related to finger movements.

METHODS

The method of the Directed Transfer Function (DTF) is a frequency-domain approach, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. Since the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites, we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. The simulation study was followed by an analysis of variance (ANOVA) of the results obtained for different levels of Signal to Noise Ratio (SNR) and temporal length, as they have been systematically imposed on simulated signals. The whole methodology was then applied to high resolution EEG data recorded during a visually paced finger movement.

RESULTS

The statistical analysis performed returns that during simulations, DTF is able to estimate correctly the imposed connectivity patterns under reasonable operative conditions, i.e. when data exhibit a SNR of at least 3 and a length of at least 75 s of non-consecutive recordings at 64 Hz of sampling rate, equivalent, more generally, to 4800 data samples.

CONCLUSIONS

Functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in any practical EEG recordings, by combining high resolution EEG techniques, linear inverse estimation and the DTF method.

SIGNIFICANCE

The estimation of cortical connectivity can be performed not only with hemodynamic measurements, by using functional MRI recordings, but also with modern EEG recordings treated with advanced computational techniques.

Evaluation of mollusks as biomonitors to investigate heavy metal contaminations along the Chinese Bohai Sea

Two gastropod species (Rapana venosa and Neverita didyma) and three bivalve species (Mytilus edulis, Crassostrea talienwhanensis and Ruditapes philippinarum) were collected from eight sites along the coastline of the Chinese Bohai Sea for the investigation of heavy metal contaminations. Cd, Co, Cu, Ni, Pb and Zn were analyzed by using pressure nebulization-inductively coupled plasma-mass spectrometer. Two certified reference materials Dogfish mussel (DORM-2) and Mussel (GBW 08571) were used to validate the methods and the obtained results proved to be in good agreement with the certified values. The results of the present study showed that Crassostrea talienwhanensis possessed a much greater ability for bioaccumulation of Cu and Zn than did the other species. Rapana venosa manifested the most bioaccumulation capacity of Cd. Among the five species, the Ruditapes philippinarum possessed the highest content of Ni. Furthermore, Cd, Cu and Zn contents in some gastropods and oysters samples exceeded the maximum permissible levels established by WHO. Due to their special bioaccumulation capacity of Cd and Ni, Rapana venosa and Ruditapes philippinarum had the potential of being used as biomonitors to control the aquatic contaminations of heavy metals.

Characterisation of Fasciola species from Mainland China by ITS-2 ribosomal DNA sequence

Isolates of Fasciola (Platyhelminthes: Trematoda: Digenea) from different host species and geographical locations in Mainland China were characterised genetically. The second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA (rDNA) was amplified from individual trematodes by polymerase chain reaction (PCR), and the representative amplicons were cloned and sequenced. The length of the ITS-2 sequences was 361-362bp for all Chinese Fasciola specimens sequenced. While there was no variation in length or composition of the ITS-2 sequences among multiple specimens from France, Sichuan and Guangxi, sequence difference of 1.7% (6/362) was detected between specimens from France and Sichuan, and those from Guangxi. Based on ITS-2 sequence data, it was concluded that the Fasciola from Sichuan represented Fasciola hepatica, the one from Guangxi represented Fasciola gigantica and the one from sheep from Heilongjiang may represent an "intermediate genotype", as its ITS-2 sequences were unique in that two different ITS-2 sequences exist in the rDNA array within a single Fasciola worm. One of the sequences is identical to that of F. hepatica, and the other is almost identical to that of F. gigantica in that nucleotides at five of the six polymorphic positions represent F. gigantica. This microheterogeneity is possibly due to sequence polymorphism among copies of the ITS-2 array within the same worm. Based on the sequence differences, a PCR-linked restriction fragment length polymorphism (PCR-RFLP) assay was established for the unequivocal delineation of the Fasciola spp. from Mainland China using restriction endonuclease Hsp92II or RcaI. This assay should provide a valuable tool for the molecular identification and for studying the ecology and population genetic structures of Fasciola spp. from Mainland China and elsewhere.

Non-invasive estimation of myocardial infarction by means of a heart-model-based imaging approach: A simulation study

In the study, a new myocardial infarction (MI) estimation method was developed for estimating MI in the three-dimensional myocardium by means of a heart-model-based inverse approach. The site and size of MI are estimated from body surface electrocardiograms by minimising multiple objective functions of the measured body surface potential maps (BSPMs) and the heart-model-generated BSPMs. Computer simulations were conducted to evaluate the performance of the developed method, using a single-site MI and dual-site MI protocols. The simulation results show that, for the single-site MI, the averaged spatial distance (SD) between the weighting centres of the 'true' and estimated MIs, and the averaged relative error (RE) between the numbers of the 'true' and estimated infarcted units are 3.0 +/- 0.6/3.6 +/- 0.6 mm and 0.11 +/- 0.02/0.14 +/- 0.02, respectively, when 5 microV/10 microV Gaussian white noise was added to the body surface potentials. For the dual-site MI, the averaged SD between the weighting centres of the 'true' and estimated MIs, and the averaged RE between the numbers of the 'true' and estimated infarcted units are 3.8 +/- 0.7/3.9 +/- 0.7mm and 0.12 +/- 0.02/0.14 +/- 0.03, respectively, when 5 microV/10 microV Gaussian white noise was added to the body surface potentials. The simulation results suggest the feasibility of applying the heart-model-based imaging approach to the estimation of myocardial infarction from body surface potentials.

Cortical potential imaging of brain electrical activity by means of parametric projection filter

OBJECTIVES

The objective of this study was to explore suitable spatial filters for inverse estimation of cortical potentials from the scalp electroencephalogram. The effect of incorporating noise covariance into inverse procedures was examined by computer simulations and tested in human experiment.

METHODS

The parametric projection filter, which allows inverse estimation with the presence of information on the noise, was applied to an inhomogeneous three-concentric-sphere model under various noise conditions in order to estimate the cortical potentials from the scalp potentials. The method for determining the optimum regularization parameter, which can be applied for parametric inverse techniques, is also discussed.

RESULTS

Human visual evoked potential experiment was carried out to examine the performance of the proposed restoration method. The parametric projection filter gave more localized inverse solution of cortical potential distribution than the truncated SVD and Tikhonov regularization.

CONCLUSION

The present simulation results suggest that incorporation of information on the noise covariance allows better estimation of cortical potentials, than inverse solutions without knowledge about the noise covariance, when the correlation between the signal and noise is low.

High-resolution EEG: cortical potential imaging of interictal spikes

BACKGROUND

It is of clinical importance to localize pathologic brain tissue in epilepsy. Noninvasive localization of cortical areas associated with interictal epileptiform spikes may provide important information to facilitate presurgical planning for intractable epilepsy patients.

METHODS

A cortical potential imaging (CPI) technique was used to deconvolve the smeared scalp potentials into the cortical potentials. A 3-spheres inhomogeneous head model was used to approximately represent the head volume conductor. Five pediatric epilepsy patients were studied. The estimated cortical potential distributions of interictal spikes were compared with the subsequent surgical resections of these same patients.

RESULTS

The areas of negativity in the reconstructed cortical potentials of interictal spikes in 5 patients were consistent with the areas of surgical resections for these patients.

CONCLUSIONS

The CPI technique may become a useful alternative for noninvasive mapping of cortical regions displaying epileptiform activity from scalp electroencephalogram recordings.