Spatio-temporal EEG source localization using simulated annealing

The estimation of multiple dipole parameters in spatio-temporal source modeling (STSM) of electroencephalographic (EEG) data is a difficult nonlinear optimization problem due to multiple local minima in the cost function. A straightforward iterative optimization approach to such a problem is very susceptible to being trapped in a local minimum, thereby resulting in incorrect estimates of the dipole parameters. In this paper, we present and evaluate a more robust optimization approach based on the simulated annealing algorithm. The complexity of this approach for the STSM problem was reduced by separating the dipole parameters into linear (moment) and nonlinear (location) components. The effectiveness of the proposed method and its superiority over the traditional nonlinear simplex technique in escaping local minima were tested and demonstrated through computer simulations. The annealing algorithm and its implementation for multidipole estimation are also discussed. We found the simulated annealing approach to be 7-31% more effective than the simplex method at converging to the true global minimum for a number of different kinds of three-dipole problems simulated in this work. In addition, the computational cost of the proposed approach was only marginally higher than its simplex counterpart. The annealing method also yielded similar solutions irrespective of the initial guesses used. The proposed simulated annealing method is an attractive alternative to the simplex method that is currently more common in dipole estimation applications.     

Recursive MUSIC: a framework for EEG and MEG source localization

The multiple signal classification (MUSIC) algorithm can be used to locate multiple asynchronous dipolar sources from electroencephalography (EEG) and magnetoencephalography (MEG) data. The algorithm scans a single-dipole model through a three-dimensional (3-D) head volume and computes projections onto an estimated signal subspace. To locate the sources, the user must search the head volume for multiple local peaks in the projection metric. This task is time consuming and subjective. Here, we describe an extension of this approach which we refer to as recursive MUSIC (R-MUSIC). This new procedure automatically extracts the locations of the sources through a recursive use of subspace projections. The new method is also able to locate synchronous sources through the use of a spatio-temporal independent topographies (IT) model. This model defines a source as one or more nonrotating dipoles with a single time course. Within this framework, we are able to locate fixed, rotating, and synchronous dipoles. The recursive subspace projection procedure that we introduce here uses the metric of canonical or subspace correlations as a multidimensional form of correlation analysis between the model subspace and the data subspace. By recursively computing subspace correlations, we build up a model for the sources which account for a given set of data. We demonstrate here how R-MUSIC can easily extract multiple asynchronous dipolar sources that are difficult to find using the original MUSIC scan. We then demonstrate R-MUSIC applied to the more general IT model and show results for combinations of fixed, rotating, and synchronous dipoles.     

Computational aspects of finite element modeling in EEG source localization

A comparison is made of two different implementations of the finite element method (FEM) for calculating the potential due to dipole sources in electroencephalography (EEG). In one formulation (the direct method) the total potential is the unknown that is solved for and the dipole source is directly incorporated into the model. In the second formulation (the subtraction method) the unknown is the difference between the total potential and the potential due to the same dipole in an infinite region of homogeneous conductivity, corresponding to the region where the dipole is located. Both methods have the same FEM system matrix. However, the subtraction method requires an additional calculation of flux integrations along the edges of the elements in the computation of the right-hand side (RHS) vector. It is shown that the subtraction method is usually more accurate in the forward modeling, provided the flux integrations are computed accurately. Errors in calculating the flux integrations may result in large errors in the forward solution due to the ill-conditioned nature of the FEM system matrix caused by the Neumann boundary condition. To minimize the errors, closed-form expressions for the flux integrations are used for both linear and quadratic triangular elements. It is also found that FEM forward modeling errors may cause false extrema in the least-square objective function obtained from the boundary potential, near boundaries between media of differing conductivity. Multiple initial guesses help eliminate the possibility of the solution getting trapped in these false extrema.     

Spatio-temporal multiple source localization by wavelet-type decomposition of evoked potentials

Scalp recording of electrical events allows evaluation of human cerebral function, but contributions of the specific brain structures generating the recorded activity are ambiguous. This problem is ill-posed and cannot be solved without auxiliary physiological knowledge about the spatio-temporal characteristics of the generators' activity. In our source localization by model-based wavelet-type decomposition, scalp recorded signals are decomposed into a combination of wavelets, each of which may describe the coherent activity of a population of neurons. We chose the Hermite functions (derived from the Gaussian function to form mono-, bi- and triphasic wave forms) as the mathematical model to describe the temporal pattern of mass neural activity. For each wavelet we solve the inverse problem for two symmetrically positioned and oriented dipoles, one of which attains zero magnitude when a single source is more suitable. We use the wavelet to model the temporal activity pattern of the symmetrical dipoles. By this we reduce the dimension of inverse problem and find a plausible solution. Once the number and the initial parameters of the sources are given, we can apply multiple source localization to correct the solution for generators with overlapping activities. Application of the procedure to subcortical and cortical components of somatosensory evoked potentials demonstrates its feasibility.     

MEG and EEG topography of frontal midline theta rhythm and source localization

PURPOSE: We studied a case of corneal ulceration in utero from lower eyelid entropion. METHODS: A 3-week-old male infant was referred for examination of a left corneal ulcer that was present at birth and unresponsive to antibiotics. RESULTS: Examination disclosed a lower eyelid entropion that was treated surgically by a nonincisional method, leaving a central leukoma after re-epithelialization. CONCLUSION: Congenital lower eyelid entropion should be included in the differential diagnosis of congenital corneal opacities.     

An efficient algorithm for computing multishell spherical volume conductor models in EEG dipole source localization

Computationally localizing electrical current sources of the electroencephalographic signal requires a volume conductor model which relates theoretical scalp potentials to the dipolar source located within the modeled brain. The commonly used multishell spherical model provides this source-potential relationship using a sum of infinite series whose computation is difficult. This paper provides a closed-form approximation to this sum based on an optimal fitting to the weights of the Legendre polynomials. The second-order (third-order) approximation algorithm, implemented by a provided C-routine, requires only 100 (140) floating point operations to compute a single scalp potential in response to an arbitrary current dipole located within a four-shell spherical volume conductor model. This cost of computation represents only 6.3% (8.9%) of that required by the direct method. The relative mean square error, measured by using 20,000 random dipoles distributed within the modeled brain, in only 0.29% (0.066%).     

Aberrant transients in the EEG of epileptic rats: a spectral analytical approach

Aberrant transients in the cortical electroencephalogram of rats of the epileptic WAG/Rij strain were studied by means of spectral analysis. The EEG of rats of this strain contains, besides normal sleep spindles, high-voltage spiky phenomena, epileptic spike-wave discharges, and deviant intermediate stage. Spectral analysis of these transient phenomena shows that some features, like their peak frequency, are alike, but that they differ in other spectral characteristics, as in the first harmonic of the peak frequency and in the domain of the high frequencies. The results provide arguments for the view that spike-wave discharges might be considered as unique aberrant phenomena, presumably related but dissimilar to the high-voltage spiky phenomena and intermediate stage. Next to this, spectral analysis was used to study the intraphenomenal dynamics of spike-wave discharges. The peak frequency was found to decrease monotonously from about 10 Hz at the beginning of the spike-wave discharge to about 8 Hz at the end. Other spike-wave discharge frequency bands showed an intraphenomenal increase followed by a decrease. These time-variant EEG dynamics in spike-wave discharges might correlate with the cognitive disturbances during absence seizures in man.     

Dipole source localization of ictal epileptiform activity

Dipole source localization of ictal epileptiform activity recorded by scalp EEG was performed in patients prior to surgical treatment. The dipole tracing method combined with the scalp-skull-brain head model was used to locate epileptogenic foci. A digital EEG system was used for data collection. The accuracy of dipole source localization was evaluated by comparing the focus location with that obtained by chronic subdural electrocorticography. In a case of frontal lobe epilepsy with epileptogenic focus in the frontoparietal convexity, the results of dipole source localization agreed well with those obtained with chronic subdural electrocorticography. In a case of lateral temporal lobe epilepsy, the results of dipole source localization were consistent with those obtained with chronic subdural electrocorticography, but a small localization error was observed. The clinical usefulness of and suggestions for improving this method are discussed.     

Activity in posterior parietal cortex following somatosensory stimulation in man: magnetoencephalographic study using spatio-temporal source analysis

The cyclin-dependent kinase (Cdk) inhibitor p21Waf1/Cip1/Sdi1, important for p53 tumor suppressor-dependent cell growth control in humans and other organisms, mediates G1/S-phase arrest through inhibition of cyclin-dependent kinases (Cdks). The enzymatic activity of these kinases is essential for progress through the cell division cycle and one level of cell cycle regulation is exerted through inhibition of Cdks by a family of small proteins, including p21. Cdk inhibition requires a sequence of approximately 60 amino acids within the p21 NH2-terminus. Using proteolytic mapping, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, HPLC and size-exclusion chromatography, we show that p21, active as a Cdk inhibitor, exists in an extended, non-globular conformation in the absence of its biological target and that p21 lacks the hallmarks of stable secondary and tertiary structure. We have developed an efficient approach to obtain detailed proteolytic maps that takes advantage of the high accuracy and sensitivity of MALDI mass spectrometry. Our method allows a proteolytic map to be obtained from a single mass spectrum for fragments produced from a single proteolytic reaction.     

An interdisciplinary team approach to implementing the ketogenic diet for the treatment of seizures

Vascular endothelial cell growth factor (VEGF) plays a pivotal role in the regulation of angiogenesis by binding to its cognate receptor molecule type II (VEGFr-II, KDR). VEGFr-II is an endothelial cell-specific transmembrane tyrosine kinase important for vascular endothelial cell development and differentiation during embryogenesis, angiogenic processes under physiological conditions, and various diseases. An increasing number of reports indicate that VEGF/VEGFr-II also play a fundamental role for tumor angiogenesis. We present the generation and in vitro characterization of the monoclonal antibodies 2-7-9 and 2-10-1. Both antibodies are highly specific for VEGFr-II as demonstrated by Western blotting and immunoprecipitation. MAbs 2-10-1 and 2-7-9 bind to a disulphide bridge-stabilized epitope within domains 6 and 7 of the human VEGFr-II with an affinity of 8 and 80 nM, respectively. Furthermore, the antibodies are suitable for immunohistochemistry and ELISA techniques. Because both antibodies recognize their epitope on living cells, they also have the potential for drug targeting and diagnostic purposes.     

Seizure detection of newborn EEG using a model-based approach

Seizures are often the first sign of neurological disease or dysfunction in the newborn. However, their clinical manifestation is often subtle, which tends to hinder their diagnosis at the earliest possible time. This represents an undesirable situation since the failure to quickly and accurately diagnose seizure can lead to longer-term brain injury or even death. In this paper we consider the problem of automatic seizure detection in the neonate based on electroencephalogram (EEG) data. We propose a new approach based on a model for the generation of the EEG, which is derived from the histology and biophysics of a localized portion of the brain. We show that by using this approach, good detection performance of electrographic seizure is possible. The model for seizure is first presented along with an estimator for the model parameters. Then we present a seizure-detection scheme based on the model parameter estimates. This scheme is compared with the quadratic detection filter (QDF), and is shown to give superior performance over the latter. This is due to the ability of the model-based detector to account for the variability (nonstationarity) of the EEG by adjusting its parameters appropriately.     

Analysis and description of the EEG by decomposition into simple elements with the aid of a micro-computer

20 patients and normal volunteers submitting to a right side heart catheterization have been subjected to hemodynamic tests before and after rapid i.v. injection of synthetic thyrotrophin releasing factor (TRF, Ro 08-6270). 10 persons among a first group were fully informed about the test, i.e. the exact time of injection, 10 others among a second group were not. A statistically significant rise of the arterial blood pressure and heart rate at an average 1-min interval after injection could be demonstrated. After 5 min the effect had completely vanished. The mean pulmonary arterial pressure like other hemodynamic parameters, the blood sugar and cholesterol did not change. A placebo-like effect could not be shown among a third group receiving only the added solvent. Because of the short interval after which the effect occurred, a determinant role of the hypothalamic-pituitary-thyroid feed back is very unlikely. A direct stimulus of TRF to smooth muscle cells of arterial walls responsible for vascular resistance in systemic vessels may be suggested as a hypothesis.     

Approximating dipoles from human EEG activity: the effect of dipole source configuration on dipolarity using single dipole models

Long-term daily administration of oral bisphosphonates has been effective in the treatment of postmenopausal osteoporosis, but the duration, mode and cost of the therapy may sometimes affect patient compliance. In Italy, the bisphosphonate clodronate is also available via the intramuscular (i.m.) route of administration, and the present study was performed to test its efficacy in postmenopausal osteoporosis. Ninety osteoporotic postmenopausal women were enrolled in a randomized, controlled 3 year study. The diet of all patients was adjusted to provide 1200-1300 mg of calcium daily, eventually by administration of supplements. Patients were randomly assigned to no therapy (30 patients) or to receive clodronate 100 mg i.m. either every 2 weeks (30 patients) or 1 week (30 patients). The i.m. injection caused substantial pain at the site of injection, which led to treatment withdrawal in almost 50% of the patients receiving weekly dosing. In control patients, a progressive, slow decline in spine and femoral bone mineral density (BMD), which became statistically significant at the end of the second year of observation, was observed. In the patients given weekly i.m. clodronate, spinal BMD rose by 3.8% (+/-7.3 SD) within 6 months. A slight, nonsignificant increase was observed thereafter, such that, at the completion of 3 years of observation, the mean gain was 4.5% (+/-6.3). In the patients treated with injections of 100 mg of clodronate every two weeks the increase in BMD was somewhat lower and slower, becoming significant only at month 24 (2.9+/-4.6%). In none of the two active groups was the femoral neck BMD changed significantly during the 3 years of the study. A significant increase in trochanter and Ward's triangle BMD was observed at month 12 only in the patients on the highest dose of clodronate. In both groups treated, the hip BMD changes were significantly different from those observed in control patients. The biochemical markers of bone turnover were suppressed in both clodronate groups. These results indicate that intermittent i.m. clodronate administration can provide clinically relevant benefits to skeletal bone density in osteoporotic postmenopausal women, but the in situ pain may limit its extensive use.     

A practical approach to implementing theraplay for children with autism spectrum disorder.

Theraplay is a counseling approach that uses elements of play therapy to help children build better attachment relationships with others through attachment-based play. This article describes a practical approach for implementing Group Theraplay with children with Autism Spectrum Disorder (ASD), particularly those that are mainstreamed in a kindergarten classroom setting. The approach uses resources that are already in place in schools today, such as mental health professionals (e.g., school counselor, social worker, etc.) and teachers. Foundational Theraplay assumptions, therapeutic goals, empirical support, and implementation guidelines are provided. Comparative effectiveness research examining the use of Group Theraplay with this population in this setting versus the use of alternative therapeutic approaches is needed. To help guide future research in this needed area of outcomes investigation, several assessment instruments appropriate for clinical research use with this population are suggested. Ethical and cultural implications pertinent to the application of Group Theraplay for children with ASD also are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A model of visual spatio-temporal memory: the icon revisited

With a minimal set of assumptions resulting from considerations about the perception of temporal structure, we argue for the existence of a spatio-temporal memory established by the mapping of time into simultaneous physical properties. The important point of this model is the distinction between external, physical time and the internal representation of time. An immediate consequence of such a structure is the emergence of properties usually associated with the concept of iconic memory or informational persistence. Some of these properties may hence be regarded as epiphenomena produced by the testing of a spatio-temporal system with tachistoscopic spatial stimuli. The model can explain properties of the immediate memory span, the lack of effect of exposure duration on tachistoscopic report, the partial-report superiority, the decay of iconic memory, and effects of a backward mask. It does not only avoid the incompatibility problems of the frozen-image concept in dynamic vision, but also provides an adequate basis for the processing of time-varying scenes.