Dipole Fitting Research Articles

P6-13 Ceftazidime induced non-convulsive status epilepticus in a uremic and stroke patient

Objective: To test the relative accuracy of two different strategies for source localization of interictal spikes. Methods: 20 patients with intractable epilepsy underwent surgery for epileptogenic focus resection. Digital EEG (21 channels 10 20 & T1T2) recorded before surgery was analyzed. Spikes were automatically searched and classified according to morphology and topography, visually screened and averaged. A dipole fitting method (BESA) and a distributed source model (eLORETA) for source localization of interictal spikes was applied to the same data. Results: Both BESA and eLORETA located sources only within the resected area (RA) in 12 patients. BESA located multiple sources, most of them inside RA with few outside RA in 2 patients and eLORETA in 4. Both methods found sources predominantly outside RA, with still some within RA in three patients. BESA showed sources only outside RA in 3 patients and eLORETA in only one. The two methods gave discordant results in 5 patients. The best match to the RA was found in patients with mesiotemporal lobe epilepsy. When analyzing the 37 independent spike clusters found across the 20 patients, BESA located the spike within RA in 22 (59.5%), in the close vicinity (same lobe) in 2, in contralateral homologous areas in 4, in another lobe but still near RA in another 5, and elsewhere in 4. Localization with eLORETA gave sources within RA in 25 cases (67%), in the same lobe in two, in contralateral homologous areas in 4, in another lobe near RA in 4 and elsewhere in 2. Discordances in localization between both methods were found for just 5 of the 37 spikes (p < 0.001). Conclusions: Both BESA and LORETA localized most interictal spikes within the resected area. Some localization discordance was found, and the best match with clinical resection decisions was achieved when using both methods together.

P6-10 Value of dipole analysis and eLORETA in the localization of EEG interictal spikes in epilepsy surgery patients

Objective: To test the relative accuracy of two different strategies for source localization of interictal spikes. Methods: 20 patients with intractable epilepsy underwent surgery for epileptogenic focus resection. Digital EEG (21 channels 10 20 & T1T2) recorded before surgery was analyzed. Spikes were automatically searched and classified according to morphology and topography, visually screened and averaged. A dipole fitting method (BESA) and a distributed source model (eLORETA) for source localization of interictal spikes was applied to the same data. Results: Both BESA and eLORETA located sources only within the resected area (RA) in 12 patients. BESA located multiple sources, most of them inside RA with few outside RA in 2 patients and eLORETA in 4. Both methods found sources predominantly outside RA, with still some within RA in three patients. BESA showed sources only outside RA in 3 patients and eLORETA in only one. The two methods gave discordant results in 5 patients. The best match to the RA was found in patients with mesiotemporal lobe epilepsy. When analyzing the 37 independent spike clusters found across the 20 patients, BESA located the spike within RA in 22 (59.5%), in the close vicinity (same lobe) in 2, in contralateral homologous areas in 4, in another lobe but still near RA in another 5, and elsewhere in 4. Localization with eLORETA gave sources within RA in 25 cases (67%), in the same lobe in two, in contralateral homologous areas in 4, in another lobe near RA in 4 and elsewhere in 2. Discordances in localization between both methods were found for just 5 of the 37 spikes (p < 0.001). Conclusions: Both BESA and LORETA localized most interictal spikes within the resected area. Some localization discordance was found, and the best match with clinical resection decisions was achieved when using both methods together.

Expiration: The moment we experience retronasal olfaction in flavor

Respiration is essential for smell perception. Previously we found that 8–12-Hz cortical rhythms were phase-locked to inspiration onset during the presentation of odor stimuli; this is referred to as inspiration phase-locked alpha band oscillation (I-α). Generators of I-α estimated with a dipole fitting model were found in the piriform, the entorhinal cortex (ENT), the amygdala (AMG), the hippocampus (HI) and the orbitofrontal cortex (OFC). Such olfactory perception is said to occur via the orthonasal olfaction route. Another route is the retronasal olfaction route. In this study, we investigated the link between respiration phase and retronasal olfactory perception. Electroencephalograph (EEG) and respiratory flows (separately measured with mouth and nose) were simultaneously recorded during stimulation of subjects’ tongues with liquids of chocolate, sucrose and water. The percentage of subjects correctly identifying the chocolate taste was higher when subjects were asked to breathe through the nose than when they were breathing through the mouth. In the averaged EEGs triggered by the onset of expiration measured from the flow through the nose, a 8–12-Hz oscillation was observed. Generators of this potential were found in the left ENT, HI, AMG and OFC in the order of milliseconds after expiration onset. Perception of retronasal olfaction is dependent on expiration, and combining retronasal olfactory information with gustatory information and somatosensation enable us to identify flavors when drinking and feeding.

EEG source analysis of epileptiform activity using a 1mm anisotropic hexahedra finite element head model

Event Abstract Back to Event EEG source analysis of epileptiform activity using a 1mm anisotropic hexahedra finite element head model Michael Rullmann1, Alfred Anwander1, Moritz Dannhauer1, Simon K. Warfield2, Frank H. Duffy3 and Carsten Wolters4* 1 Max Planck Institute for Human Cognitive and Brain Sciences, Germany 2 Harvard Medical School, Computational Radiology Laboratory, Children's Hospital, United States 3 Harvard Medical School, Department of Neurology, Children's Hospital, United States 4 Institute for Biomagnetism and Biosignalanalysis, Germany The major goal of the evaluation in presurgical epilepsy diagnosis for medically intractable patients is the precise reconstruction of the epileptogenic foci, preferably with non-invasive methods. We evaluated whether surface electroencephalography (EEG) source analysis based on a 1mm anisotropic finite element (FE) head model can provide additional guidance for presurgical epilepsy diagnosis and whether it is practically feasible in daily routine. A 1mm hexahedra FE volume conductor model of the patient's head with special focus on accurately modeling the compartments skull, cerebrospinal fluid (CSF) and the anisotropic conducting brain tissues was constructed using non-linearly co-registered T1-, T2- and diffusion-tensor- magnetic resonance imaging data. The electrodes of intra-cranial EEG (iEEG) measurements were extracted from a co-registered computed tomography image. Goal function scan (GFS), minimum norm least squares (MNLS), standardized low resolution electromagnetic tomography (sLORETA) and spatio-temporal current dipole modeling inverse methods were then applied to the peak of the averaged ictal discharges EEG data. MNLS and sLORETA pointed to a single center of activity. Moving and rotating single dipole fits resulted in an explained variance of more than 97%. The non-invasive EEG source analysis methods localized at the border of the lesion and at the border of the iEEG electrodes which mainly received ictal discharges. Source orientation was towards the epileptogenic tissue. For the reconstructed superficial source, brain conductivity anisotropy and the lesion conductivity had only a minor influence, whereas a correct modeling of the highly conducting CSF compartment and the anisotropic skull was found to be important. The proposed FE forward modeling approach strongly simplifies meshing and reduces run-time (37 Milliseconds for one forward computation in the model with 3.1 Million unknowns), corroborating the practical feasibility of the approach. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Epilepsy Citation: Rullmann M, Anwander A, Dannhauer M, Warfield SK, Duffy FH and Wolters C (2010). EEG source analysis of epileptiform activity using a 1mm anisotropic hexahedra finite element head model. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00306 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Apr 2010; Published Online: 05 Apr 2010. * Correspondence: Carsten Wolters, Institute for Biomagnetism and Biosignalanalysis, Munster, Germany, carsten.wolters@uni-muenster.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Michael Rullmann Alfred Anwander Moritz Dannhauer Simon K Warfield Frank H Duffy Carsten Wolters Google Michael Rullmann Alfred Anwander Moritz Dannhauer Simon K Warfield Frank H Duffy Carsten Wolters Google Scholar Michael Rullmann Alfred Anwander Moritz Dannhauer Simon K Warfield Frank H Duffy Carsten Wolters PubMed Michael Rullmann Alfred Anwander Moritz Dannhauer Simon K Warfield Frank H Duffy Carsten Wolters Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The Effect of Spatiotemporal Signal Space Separation (tSSS) on the Localization of Interictal Spikes

Event Abstract Back to Event The Effect of Spatiotemporal Signal Space Separation (tSSS) on the Localization of Interictal Spikes Michael Funke1* and Samu Taulu2 1 University of Utah, United States 2 Elekta Oy, Finland Introduction: An increasing number of patients with intractable epilepsy are being treated with the vagus nerve stimulator (VNS) while in pursuit of resective neurosurgery. In addition, significant artifact contamination can be caused due to prior craniotomies and dental work. Processing such artifact contaminated clinical data using tSSS seems a promising solution for interference removal. But can localization results obtained from tSSS processed data be trusted? In this study, we investigate the effect of the tSSS on the localization of interictal transients in uncontaminated data sets. Methods: MEG data from ten (10) clinical patients with intractable epilepsy were acquired with a 306-channel whole-head MEG system. Simultaneous EEG was recorded using a 60-channel electrode array. Sleep was induced by prior sleep deprivation. Approximately 60 minutes of continuous data were recorded. None of the patients demonstrated significant artifacts. The spatiotemporal signal space separation method (tSSS) [1], an extended version of the spatial SSS [2], was applied off-line to the raw data. For each patient data were and bandpass filtered 1-70 Hz and ten (10) interictal spikes were localized using all 102 magnetometers and 204 gradiometers. Localization results for a single dipole fit, Goodness of Fit (GOF) as well as the Confidence Volume were compared for raw data as well as the for tSSS processed data. Resuts: The localization results between raw data and tSSS processed data across subjects showed a difference of 1.69 mm (SD: 0.52 mm; range: 1.10 mm - 2.41 mm). The GOF differences across subjects improved on average by 12.59% (SD: 4.82%; range: 5.55% - 18.10%). The Confidence volume decreased by 0.02 mm³ (SD: 0.04 mm³; range: 0 mm³ - 0.08 mm³). Conclusions: Source localization of interictal spikes in tSSS filtered data changed the localization on average by less than 2 mm, compared to unfiltered data, while GOF of the fitted dipoles increased noticeably. The Confidence Volume decreased minimally. Overall, tSSS seems to have very little effect on the localization of interictal spikes but improves the GOF due to noise reduction, ergo increasing slightly the SNR of epileptiform transients.

Realistic models of spatially extended cortical activity in MEG

Event Abstract Back to Event Realistic models of spatially extended cortical activity in MEG Douglas Cheyne1*, Jason Lerch2, Ismail Mohamed3, Paul Ferrari4, Marc Lalancette5 and Elizabeth Pang5 1 University of Toronto, Program in Clinical and Experimental Therapeutics, Department of Clinical and Administrative Pharmacy, Canada 2 Hospital for Sick Children and Toronto Centre for Phenogenomics, Program in Neurosciences and Mental Health, Canada 3 Alberta Children's Hospital, Department of Pediatrics, Canada 4 Hospital for Sick Children, Program in Neurosciences and Mental Health, Canada 5 Hospital for Sick Children, Program in Neurosciences and Mental Health and Division of Neurology, Canada Magnetic fields detectable at the scalp surface are generated by large populations of synchronously active neurons. In particular, large amplitude epileptic discharges (spikes) may involve cortical areas up to several cm^2 [1] and it has been argued that localization methods based on point sources will result in erroneous localization for such large extended sources [2]. However, realistic models of sources in MEG must take into account attenuation of radially oriented currents and cancelling currents in sulcal walls [3]. We modeled extended cortical patches in the sensorimotor region using high-resolution cortical surface meshes derived from MRI [4] based on averaged motor fields in a healthy adult, and Rolandic interictal spikes in a 12-year old female patient, recorded with a 151-channel CTF MEG. Simulated cortical patches 14 to 2400 mm^2 in size with uniform current density (approx. 0.5 nAm/mm^2) were added to background brain activity and localized using a single dipole fit and event-related beamformer (ERB) [5]. Larger patches (> 6 cm^2) produced either very weak fields (due to cancellation), or dipolar fields with low error single dipole fits, but to regions of the patch rather than at greater depths, confirming that involvement of multiple gyri and sulci will appear as either attenuated or fragmented source patterns in MEG, rather than large uniform sources. Interestingly, ERB localization revealed both single and multiple peaks for the larger patches and was not completely suppressed due to correlated activity across the extended source. We conclude that use of physiologically realistic models is important for evaluating the effect of spatially extended brain activity on MEG localization methods.

Influence of homogenous and inhommogenous magnetic field disturbances on the localization uncertainty of a magnetic dipole fit

Event Abstract Back to Event Influence of homogenous and inhommogenous magnetic field disturbances on the localization uncertainty of a magnetic dipole fit Uwe Steinhoff1*, Frank Wiekhorst1, Daniel Baumgarten2, 3, Jens Haueisen2, 3 and Lutz Trahms1 1 Physikalisch-Technische Bundesanstalt, Germany 2 Ilmenau University of Technology, Germany 3 University Hospital Jena, Germany For relaxation measurements of magnetic nanoparticles in larger objects, the object has to be magnetized by a field of a few millitesla or more prior to the measurement. In order to avoid the exposure of SQUID sensors to such high fields, the magnetization usually is done outside the magnetically shielded room. After magnetization, the sample is rapidly transferred to the measurement position in the shielded room. Since the door has to be left open for this procedure, the magnetic noise level in the room is increased by external disturbances penetrating through the open door. Under these unfavorable shielding conditions in the Berlin magnetically shielded room BMSR-2, we identified a temporally slowly varying homogeneous magnetic field with an amplitude up to 15 pT and a vertical gradient of up to 20 pT/m pointing into the door direction as the main noise components. To study the influence of these noise contributions on the localization and quantification results of a non-linear magnetic dipole fit, we simulated a point-like source on a regular grid within a cylindrical measurement volume centred below our 304 channel vector magnetometer system. After adding the noise contributions with different SNRs, we localized the source using a non-linear Levenberg-Marquardt algorithm. Our results show that a homogenous offset noise leads to a radially symmetric moment underestimation for central sources together with a decreasing distance between fitted source position and sensors. For sources in exterior regions the moments are overestimated and the distance to the sensors and off the centre is increased. A gradient noise leads to a misfit in the moments according to the gradient plane direction and at the same time to an opposite in- or decreasing of the distances between the fitted sources and the sensors. From these results, the uncertainty distributions of position and magnetic moment for both types of noise contributions as a function of the SNR are deduced. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Nanoparticles, Biosusceptometry and Effects of Magnetic Fields Citation: Steinhoff U, Wiekhorst F, Baumgarten D, Haueisen J and Trahms L (2010). Influence of homogenous and inhommogenous magnetic field disturbances on the localization uncertainty of a magnetic dipole fit. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00407 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 09 Apr 2010; Published Online: 09 Apr 2010. * Correspondence: Uwe Steinhoff, Physikalisch-Technische Bundesanstalt, Berlin, Germany, uwe.steinhoff@ptb.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Uwe Steinhoff Frank Wiekhorst Daniel Baumgarten Jens Haueisen Lutz Trahms Google Uwe Steinhoff Frank Wiekhorst Daniel Baumgarten Jens Haueisen Lutz Trahms Google Scholar Uwe Steinhoff Frank Wiekhorst Daniel Baumgarten Jens Haueisen Lutz Trahms PubMed Uwe Steinhoff Frank Wiekhorst Daniel Baumgarten Jens Haueisen Lutz Trahms Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

EMPIRICAL MODE DECOMPOSITION METHOD FOR MEG PHANTOM DATA ANALYSIS

Magnetoencephalography (MEG) is a powerful and non-invasive technique for measuring human brain activity with a high temporal resolution. The motivation for studying MEG data analysis is to extract the essential features from real-world measured data and represent them corresponding to the human brain functions. This usually depends on how to reduce a high level noise from the measurement. In this paper, a novel multistage MEG data analysis method based on the empirical mode decomposition (EMD) and independent component analysis (ICA) approaches is proposed for the feature extraction. Moreover, EMD and ICA algorithms are investigated for analyzing the MEG single-trial data which is recorded from the experiment of phantom. The analyzed results are presented to illustrate the effectiveness and high performance both in high level noise reduction by EMD associated with ICA approach and source localization by equivalent current dipole fitting method.

Source Localization of EEG/MEG Data by Correlating Columns of ICA and Lead Field Matrices

Independent components analysis (ICA) has previously been used to denoise EEG/magnetoencephalography (MEG) signals before performing neural source localization. Source localization is then performed using a method such as beamforming or dipole fitting. Here we show how ICA can also be used as a source localization method, negating the need for beamforming and dipole fitting. This type of approach is valid whenever an estimate of the forward (mixing) model for all putative source locations is available, which includes EEG and MEG applications. The proposed method consists of estimating the forward model using the laws of physics, estimating a second forward model using ICA, and then correlating the columns of the matrices that represent the two forward models. We show that, when synthetic data are used, the proposed localization method produces a smaller localization error than several alternatives. We also show localization results for real auditory-evoked MEG data.

Alternative cerebral generators and circuitry pathways in alpha coma revealed by independent component analysis

This study investigates the generators of alpha coma activity and the probable cerebral pathways involved in alpha coma patients. This study uses independent component analysis (ICA) and dipole fitting algorithm to locate the cerebral generators in alpha coma and normal alpha rhythms. Distinct distributions of the source generators for alpha activity were noted in alpha coma. They were localized to the anterior neocortical and subcortical regions, which includes caudate nucleus, midbrain and hypothalamus. In addition, the two patients who survive long term have five independent components identified vs. the other five patients who demised only had one or two independent components. The findings showed that alpha activity could be generated using alternative generators and pathways. This is probably due to the disinhibition of the normally inhibited pathways in coma. The presence of less independent components is probably a marker of less preserved brain tissue and predicts worse outcome. This is the first known human study using the ICA method to localize the cerebral generators in alpha coma. It might provide a new dimension of interpreting clinical EEGs in patients with alpha coma. It also might have significant application in predicting the clinical outcomes.

Source localisation in concurrent EEG/fMRI: Applications at 7T

This paper investigates the application of source reconstruction methodologies to EEG data recorded in concurrent EEG/fMRI experiments at 7T. An EEG phantom containing a dipolar current source is described and used to investigate the accuracy of source localisation. Both dipole fitting and beamformer algorithms are shown to yield accurate locations for the dipole within the phantom. Source reconstruction methodologies are also shown to reduce significantly the level of interference in the recorded EEG, caused by the MR scanner. A comparison between beamformer and dipole fitting approaches is made and it is shown that, due to its adaptive weighting parameters, the beamformer provides better suppression of interference when compared to the dipole fit. In addition it is shown that, in the case of the beamformer, use of a high EEG channel density improves the level of interference reduction, and the ratio of measured signal to interference can be improved by a factor of ∼1.6 if the number of EEG electrodes is increased from 32 to 64. The interference reduction properties of source localisation are shown theoretically, in simulation, and in phantom data. Finally, in-vivo experiments conducted at 7T show that effects in the gamma band can be recorded using simultaneous EEG/fMRI. These results are achieved by application of beamformer methodology to 64 channel EEG data.

Magnetic nanoparticle imaging by means of minimum norm estimates from remanence measurements

In magnetic nanoparticle imaging, magnetic nanoparticles are coated and functionalized to bind to specific targets. After measuring their magnetic relaxation or remanence, their distribution can be determined by means of inverse methods. The reconstruction algorithm presented in this paper includes first a dipole fit using a Levenberg-Marquardt optimizer to determine the reconstruction plane. Secondly, a minimum norm estimate is obtained on a regular grid placed in that plane. Computer simulations involving different parameter sets and conditions show that the used approach allows for the reconstruction of distributed sources, although the reconstructed shapes are distorted by blurring effects. The reconstruction quality depends on the signal-to-noise ratio of the measurements and decreases with larger sensor-source distances and higher grid spacings. In phantom measurements, the magnetic remanence of nanoparticle columns with clinical relevant sizes is determined with two common measurement systems. The reconstructions from these measurements indicate that the approach is applicable for clinical measurements. Our results provide parameter sets for successful application of minimum norm approaches to Magnetic Nanoparticle Imaging.

EEG source analysis of epileptiform activity using a 1 mm anisotropic hexahedra finite element head model

The major goal of the evaluation in presurgical epilepsy diagnosis for medically intractable patients is the precise reconstruction of the epileptogenic foci, preferably with non-invasive methods. This paper evaluates whether surface electroencephalography (EEG) source analysis based on a 1 mm anisotropic finite element (FE) head model can provide additional guidance for presurgical epilepsy diagnosis and whether it is practically feasible in daily routine. A 1 mm hexahedra FE volume conductor model of the patient's head with special focus on accurately modeling the compartments skull, cerebrospinal fluid (CSF) and the anisotropic conducting brain tissues was constructed using non-linearly co-registered T1-, T2- and diffusion-tensor-magnetic resonance imaging data. The electrodes of intra-cranial EEG (iEEG) measurements were extracted from a co-registered computed tomography image. Goal function scan (GFS), minimum norm least squares (MNLS), standardized low resolution electromagnetic tomography (sLORETA) and spatio-temporal current dipole modeling inverse methods were then applied to the peak of the averaged ictal discharges EEG data. MNLS and sLORETA pointed to a single center of activity. Moving and rotating single dipole fits resulted in an explained variance of more than 97%. The non-invasive EEG source analysis methods localized at the border of the lesion and at the border of the iEEG electrodes which mainly received ictal discharges. Source orientation was towards the epileptogenic tissue. For the reconstructed superficial source, brain conductivity anisotropy and the lesion conductivity had only a minor influence, whereas a correct modeling of the highly conducting CSF compartment and the anisotropic skull was found to be important. The proposed FE forward modeling approach strongly simplifies meshing and reduces run-time (37 ms for one forward computation in the model with 3.1 million unknowns), corroborating the practical feasibility of the approach.

Two-component model for the axial form factor of the nucleon

The axial form factor of the nucleon is studied in a two-component model consisting of a three-quark intrinsic structure surrounded by a meson cloud. The experimental data in the space-like region are well reproduced with a minimal number of parameters. The results are similar to those obtained from a dipole fit for $0l{Q}^{2}l1 {\mathrm{GeV}}^{2}$, but outside this region there are important deviations from the dipole parametrization. Finally, the theoretical formula for the axial form factor is extrapolated by analytic continuation to the time-like region, thus providing the first predictions in this kinematical region which is of interest for present and future colliders.

Magnetic Response of Clustered UXO Targets

The objective of many recent UXO surveys has been described as “wide-area assessment” with the purpose of obtaining better definition of a known problem area. The targets of interest are clusters of ordnance, fragments and debris which are all indicators of greater contamination, higher risk of UXO hazard and higher remediation or construction costs. This is a different problem from the detection and discrimination of individual anomalies. This paper provides a definition of a “cluster” based on the amount of overlap between individual dipole signatures. In total field surveys, magnetic anomalies overlap significantly and show an increased amplitude response once the individual sources are spaced closer than 0.5 times the sensor height. When this condition is extended over a large area, such as the center of a target site, the result can be comparable to a horizontal sheet of dipoles. The equations to simulate a horizontal sheet are derived, and from these the relative density of targets may be calculated from the measured data by assuming a nominal target moment. Two field tests support both the qualitative and quantitative predictions. Extending this concept to field practice, we examine some of the implications for standard operational procedures. For example, if we accept that QA/QC metrics should represent the targets of interest, then we should require wide-area assessment surveys to create impractically large grids of surface frag. Likewise, for detection of clusters the concepts of detection probability and search radius based on single items are irrelevant. Discrimination techniques that rely on dipole fitting will be extremely inaccurate. Instead, QA parameters and models suitable for horizontal sheets will have to be derived.

A distributed spatio-temporal EEG/MEG inverse solver

We propose a novel ℓ1ℓ2-norm inverse solver for estimating the sources of EEG/MEG signals. Based on the standard ℓ1-norm inverse solvers, this sparse distributed inverse solver integrates the ℓ1-norm spatial model with a temporal model of the source signals in order to avoid unstable activation patterns and “spiky” reconstructed signals often produced by the currently used sparse solvers. The joint spatio-temporal model leads to a cost function with an ℓ1ℓ2-norm regularizer whose minimization can be reduced to a convex second-order cone programming (SOCP) problem and efficiently solved using the interior-point method. The efficient computation of the SOCP problem allows us to implement permutation tests for estimating statistical significance of the inverse solution. Validation with simulated and human MEG data shows that the proposed solver yields source time course estimates qualitatively similar to those obtained through dipole fitting, but without the need to specify the number of dipole sources in advance. Furthermore, the ℓ1ℓ2-norm solver achieves fewer false positives and a better representation of the source locations than the conventional ℓ2 minimum-norm estimates.

Temperature influence on the energy of nonspecific and specific interactions taking place between 4-aminophthalimide (4-AP) and homogeneous solvents

Temperature induced spectral shifts of the 4-aminophthalimide (4-AP) emission spectra have been measured and compared to the predictions of the McRae solvent induced shift theory (J. Phys. Chem., 1957, 61, 562-572). Three moderately polar chloroalkanes selected as nonspecifically interacting media, and six hydrogen accepting or/and electron pair donating solvents have been used as the media in which the temperature influence on 4-AP-solvent interactions has been studied in the range of 180-320 K. Using the ab initio determined 4-AP ground state dipole moment and fitting appropriate expression originating from the mentioned theory to the shifts found in the chloroalkanes it has been possible to estimate the 4-AP excited state dipole moment, the probe excited state Onsager radius and its gas phase emission spectrum position. Using these values the thermochromic shifts of 4-AP emission spectra in hydrogen bond forming solvents have been predicted and compared to the experimental one. Temperature has been found to have different impact on the changes, upon excitation of the probe, in the mean values of the energies of different hydrogen bonds formed by 4-AP with solvents molecules.

Predicting Reaching Targets from Human EEG

Extracting reach information from brain signals is of great interest to the fields of brain-computer interfaces (BCIs) and human motor control. To date, most work in this area has focused on invasive intracranial recordings; however, successful decoding of reach targets from noninvasive electroencephalogram (EEG) signals would be of great interest. In this article, we show that EEG signals contain sufficient information to decode target location during a reach (Experiment 1) and during the planning period before a reach (Experiment 2). We discuss the application of independent component analysis and dipole fitting for removing movement artifacts. With this technique we get similar classification accuracy for classifying EEG signals during a reach (Experiment 1) and during the planning period before a reach (Experiment 2). To the best of our knowledge, this is the first demonstration of decoding (planned) reach targets from EEG. These results lay the foundation for future EEG-based BCIs based on decoding of planned reaches.

An automatic procedure for the analysis of electric and magnetic mismatch negativity based on anatomical brain mapping

Data processing techniques in electroencephalography (EEG) and magnetoencephalography (MEG) need user interactions. However, particularly in clinical applications, fast and objective data processing is important. Here we present an observer-independent method for EEG and MEG analysis of mismatch negativity (MMN) that allows reliable estimation of source activity based on objective anatomical references. The procedure integrates several steps including artifact rejection, source estimation and statistical analysis. It enables the evaluation of source activity in a fully automatic and unsupervised manner. To test its feasibility we obtained EEG and MEG responses in an auditory oddball paradigm in 12 healthy volunteers. The automatized method of EEG and MEG data analysis estimated source activity. The automatically detected MMN was closely comparable with the results obtained by a user-controlled method based on the dipole fitting. The presented workflow can be performed easily, rapidly, and reliably. This development may open new fields in research and clinical applications of source-based EEG and MEG.

Abnormal oscillatory brain dynamics in schizophrenia: a sign of deviant communication in neural network?

BackgroundSlow waves in the delta (0.5–4 Hz) frequency range are indications of normal activity in sleep. In neurological disorders, focal electric and magnetic slow wave activity is generated in the vicinity of structural brain lesions. Initial studies, including our own, suggest that the distribution of the focal concentration of generators of slow waves (dipole density in the delta frequency band) also distinguishes patients with psychiatric disorders such as schizophrenia, affective disorders, and posttraumatic stress disorder.MethodsThe present study examined the distribution of focal slow wave activity (ASWA: abnormal slow wave activity) in116 healthy subjects, 76 inpatients with schizophrenic or schizoaffective diagnoses and 42 inpatients with affective (ICD-10: F3) or neurotic/reactive (F4) diagnoses using a newly refined measure of dipole density. Based on 5-min resting magnetoencephalogram (MEG), sources of activity in the 1–4 Hz frequency band were determined by equivalent dipole fitting in anatomically defined cortical regions.ResultsCompared to healthy subjects the schizophrenia sample was characterized by significantly more intense slow wave activity, with maxima in frontal and central areas. In contrast, affective disorder patients exhibited less slow wave generators mainly in frontal and central regions when compared to healthy subjects and schizophrenia patients. In both samples, frontal ASWA were related to affective symptoms.ConclusionIn schizophrenic patients, the regions of ASWA correspond to those identified for gray matter loss. This suggests that ASWA might be evaluated as a measure of altered neuronal network architecture and communication, which may mediate psychopathological signs.