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PubMed2006

Tri-polar concentric ring electrode development for laplacian electroencephalography.

Brain activity generates electrical potentials that are spatio-temporal in nature. Electroencephalography (EEG) is the least costly and most widely used noninvasive technique for diagnosing many brain problems. It has high temporal resolution, but lacks high spatial resolution. In an attempt to increase the spatial selectivity, researchers introduced a bipolar electrode configuration utilizing a five-point finite difference method (FPM) and others applied a quasi-bipolar (tri-polar with two elements shorted) concentric electrode configuration. To further increase the spatial resolution, the authors report on a tri-polar concentric electrode configuration for approximating the analytical Laplacian based on a nine-point finite difference method (NPM). For direct comparison, the FPM, quasi-bipolar method (a hybrid NPM), and NPM were calculated over a 400 x 400 mesh with 1/400 spacing using a computer model. A closed-form analytical computer model was also developed to evaluate and compare the properties of concentric bipolar, quasi-bipolar, and tri-polar electrode configurations, and the results were verified with tank experiments. The tri-polar configuration and the NPM were found to have significantly improved accuracy in Laplacian estimation and localization. Movement-related potential (MRP) signals were recorded from the left prefrontal lobes on the scalp of human subjects while they performed fast repetitive movements. Disc, bipolar, quasi-bipolar, and tri-polar electrodes were used. MRP signals were plotted for all four electrode configurations. The signal-to-noise ratio and spatial selectivity of the MRP signals acquired with the tri-polar electrode configuration were significantly better than the other configurations.

Adult↗
PubMed2006

Estimating parametric line-source models with electroencephalography.

We develop three parametric models for electroencephalography (EEG) to estimate current sources that are spatially distributed on a line. We assume a realistic head model and solve the EEG forward problem using the boundary element method (BEM). We present the models with increasing degrees of freedom, provide the forward solutions, and derive the maximum-likelihood estimates as well as Cramér-Rao bounds of the unknown source parameters. A series of experiments are conducted to evaluate the applicability of the proposed models. We use numerical examples to demonstrate the usefulness of our line-source models in estimating extended sources. We also apply our models to the real EEG data of N20 response that is known to have an extended source. We observe that the line-source models explain the N20 measurements better than the dipole model.

Action Potentials↗
PubMed2006

Parametric surface-source modeling and estimation with electroencephalography.

Electroencephalography (EEG) is an important tool for studying the brain functions and is becoming popular in clinical practice. In this paper, we develop four parametric EEG models to estimate current sources that are spatially distributed on a surface. Our models approximate the source shape and extent explicitly and can be applied to localize extended sources which are often encountered, e.g., in epilepsy diagnosis. We assume a realistic head model and solve the EEG forward problem using the boundary element method. We present the source models with increasing degrees of freedom, provide the forward solutions, and derive the maximum-likelihood estimates as well as Cramér-Rao bounds of the unknown source parameters. In order to evaluate the applicability of the proposed models, we first compare their estimation performances with the dipole model's using several known source distributions. We then discuss the conditions under which we can distinguish between the proposed extended sources and the focal dipole using the generalized likelihood ratio test. We also apply our models to the electric measurements obtained from a phantom body in which an extended electric source is imbedded. We observe that the proposed model can capture the source extent information satisfactorily and the localization accuracy is better than the dipole model.

Action Potentials↗
PubMed2005

Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography.

PURPOSE: Objectively to evaluate whether independent spike detection by human interpreters is clinically valid in magnetoencephalography (MEG) and to characterize detection differences between MEG and scalp electroencephalography (EEG). METHODS: We simultaneously recorded scalp EEG and MEG data from 43 patients with intractable focal epilepsy. Raw EEG and MEG waveforms were reviewed independently by two experienced epileptologists, one for EEG and one for MEG, blinded to the other modality and to the clinical information. The number and localization of spikes detected by EEG and/or MEG were compared in relation to clinical diagnosis based on postoperative seizure freedom. RESULTS: Interictal spikes were captured in both EEG and MEG in 31, in MEG alone in eight, in EEG alone in one, and in neither modality in three patients. The number of detections ranged widely with no statistical difference between modalities. A median of 25.7% of total spikes was detectable by both modalities. Spike localization was similarly consistent with the epilepsy diagnosis in 85.2% (EEG) and 78.1% (MEG) of the patients. Inaccurate localization occurred only in those cases with very few spikes detected, especially when the detections were in one modality alone. CONCLUSIONS: Interictal epileptiform discharges are easily perceived in MEG. Independent spike identification in MEG can provide clinical results comparable, but not superior, to EEG. Many spikes were seen in only one modality or the other; therefore the use of both EEG and MEG may provide additional information.

Adolescent↗
PubMed1998

Topographic mapping of electroencephalography coherence in hypnagogic state.

The present study examined the topographic characteristics of hypnagogic electroencephalography (EEG), using topographic mapping of EEG power and coherence corresponding to nine EEG stages (Hori's hypnagogic EEG stages). EEG stages 1 and 2, the EEG stages 3-8, and the EEG stage 9 each correspond with standard sleep stage W, 1 and 2, respectively. The dominant topographic components of delta and theta activities increased clearly from the vertex sharp-wave stage (the EEG stages 6 and 7) in the anterior-central areas. The dominant topographic component of alpha 3 activities increased clearly from the EEG stage 9 in the anterior-central areas. The dominant topographic component of sigma activities increased clearly from the EEG stage 8 in the central-parietal area. These results suggested basic sleep process might start before the onset of sleep stage 2 or of the manually scored spindles.

Adult↗
PubMed1997

The concurrent recording of electroencephalography and impedance cardiography: effects on EEG.

Three experiments were performed testing the effects of a variety of impedance cardiograph electrode types and recording arrangements on recorded electroencephalography (EEG) using either a monopolar single-ear reference or a physically linked ears reference. EEG was recorded either alone or concurrently with an impedance cardiograph. When the cardiograph was recorded using a spot electrode for the top current-inducing electrode, there was an overall decrease in power density of the EEG, and this effect was dependent on the location of the recording electrode. This effect was diminished when the top cardiograph spot electrode was replaced by a mylar-coated neck band electrode and EEG was recorded using a monopolar, single-ear reference. However, there tended to be an overall increase in log power density of the EEG in each frequency band below 60 Hz when less technologically advanced EEG amplifiers were used. This effect was diminished if the EEG was recorded using a physically linked ears reference. Recommendations for the concurrent recording of EEG and impedance cardiography are discussed.

Adolescent↗
PubMed2006

Quantitative electroencephalography values of neonates during and after venoarterial extracorporeal membrane oxygenation and permanent ligation of right common carotid artery.

Venoarterial extracorporeal membrane oxygenation (ECMO) in neonates commonly needs neck vessel cannulation leading to ligation of right common carotid artery (RCCA) in some cases. Quantitative electroencephalography (EEG) measurements provide reproducible data of cerebral function. The aim of this case-control study was to test whether ligation of the RCCA results in EEG changes after ECMO weaning. Ten mechanically ventilated neonates not treated with ECMO were eligible as control patients. Seven ECMO patients receiving similar sedoanalgesia were investigated during and after ECMO and RCCA ligation. Dominant frequency, absolute alpha, theta, delta, and total powers of right and left frontocentral and temporooccipital derivations were calculated. Dominant frequency did not differ among groups. Power was found to be significantly decreased in all frequency bands during ECMO. After weaning from ECMO, EEG differences between the ECMO and control groups disappeared in spite of permanent RCCA ligation. It is concluded that ligation of the RCCA per se does not result in quantitative EEG changes.

Carotid Artery, Common↗
PubMed1979

Recording small sharp spikes with depth electroencephalography.

Two patients with intractable seizures and focal temporal sharp waves also had small sharp spikes as incidental findings in their scalp electroencephalograms. Depth electroencephalography verified the intracerebral origin of the small sharp spikes and differentiated them from the more significant epileptiform abnormalities.

Adolescent↗
PubMed2003

Relationship of the model for end-stage liver disease (MELD) scale to hepatic encephalopathy, as defined by electroencephalography and neuropsychometric testing, and ascites.

OBJECTIVE: It has recently been suggested that the Model for End-Stage Liver Disease (MELD) is a better and a more objective predictor of mortality in patients with end-stage liver disease. The aim of our study was to determine the relationship of the MELD score to hepatic encephalopathy (HE), as determined by electroencephalography (EEG) and clinical and neuropsychometric examination, and ascites. METHODS: A total of 66 patients underwent EEG, a neuropsychometric screening by Mini-Mental State Examination, Trails Making Tests, Rey-Osterreith Complex Figure, and Hopkins Verbal Learning Tests, and a clinical assessment for HE. The MELD score was calculated as previously described by using serum creatinine, bilirubin, and international normalized ratio. Subclinical HE was diagnosed if clinical examination did not detect HE but neuropsychometric tests and EEG were abnormal. RESULTS: Sixteen patients had no HE, 28 had subclinical HE, and 22 had clinical HE. Age, sex, race, and cause of liver disease were similar in all three groups. Child-Turcotte-Pugh score was significantly higher in patients with clinical HE compared with the other two groups. There was only a modest correlation (r = 0.5) between Child-Turcotte-Pugh and the MELD scores. The distribution and mean MELD scores were similar in patients with or without HE as determined by clinical or neuropsychometric examination and EEG. Approximately 90% of patients with clinical HE or abnormal EEG and neuropsychometric tests had a MELD score less than 25. Similarly, the MELD score was not affected by the severity of ascites. CONCLUSION: The MELD score does not correlate well with severity of HE or ascites. Patients with HE and ascites might not receive liver transplantation in a timely manner if MELD scores were to be used exclusively for organ allocation.

Adult↗
PubMed1994

Quantitative electroencephalography in idiopathic normal pressure hydrocephalus: relationship to CSF outflow resistance and the CSF tap-test.

Quantitative electroencephalography from the occipito-parietal region, gait, and psychometric tests were performed in patients with idiopathic normal pressure hydrocephalus (NPH) before and after drainage of 40 ml CSF. The results were compared to those in demented controls. The EEG results were also analyzed with respect to possible correlations with clinical, CSF dynamics, and psychometric variables. Significant differences between NPH patients and demented controls were not found neither in baseline EEG variables nor regarding the CSF tap-test-related change in EEG. The EEG-response to the CSF tap-test did not often exceed the day-to-day test-retest variability. In NPH patients, EEG slowing (relative delta and theta power) correlated significantly with CSF outflow-resistance (p < 0.002). Relative theta power correlated with the Thurstone's Identical Forms test (p < 0.05). Significant correlations between EEG and Bingley's Memory Test were found for the control group but not among NPH patients (p < 0.05). Thus, EEG band-power variables seem to reflect some of the pathophysiology involved in idiopathic normal pressure hydrocephalus, particularly increased resistance to CSF outflow. The practical value of the presently applied EEG method in NPH-diagnosis and prognostic evaluation seems to be limited, however.

Adult↗
PubMed1996

Use of electroencephalography to detect Alzheimer's disease in Down's syndrome.

We studied the role of electroencephalography (EEG) in the diagnosis of Alzheimer-type dementia in patients with Down's syndrome. 197 patients with Down's syndrome were monitored for 5 to 8 years. Aspects of cognitive functioning were assessed twice yearly. EEGs were scored in a blind fashion, and changes in the EEG were compared to changes in cognitive functioning. When possible, a neuropathological post-mortem examination was performed. Cognitive functioning was drastically reduced in 29 patients. The dominant occipital rhythm became slower at the onset of the cognitive deterioration, and eventually disappeared. In 11 of these patients neuropathological examination showed a severe form of Alzheimer's disease. Changes in the frequency of the dominant occipital rhythm could distinguish between Alzheimer's disease or other causes as underlying the cognitive decline. Slowing of the dominant occipital rhythm seems to be related to Alzheimer's disease in patients with Down's syndrome, and the frequency of the dominant occipital activity decreases at the onset of cognitive deterioration. The EEG is thus an important tool in the clinical diagnosis of Alzheimer-type dementia in patients with Down's syndrome.

Adult↗
PubMed1990

The effects of total sleep deprivation and subsequent treatment with clomipramine on depressive symptoms and sleep electroencephalography in patients with a major depressive disorder.

In the present study patients with a major depressive disorder were first subjected to total sleep deprivation (TSD) and then treated with clomipramine. Sleep electroencephalography (EEG) was registered prior to and after TSD, during the 2 initial nights of antidepressive treatment and after 19 days. A negative correlation between response to TSD and clomipramine was found. TSD did not differentially influence the sleep EEG (responders vs nonresponders): responders tended, however, to show a more classical depressive sleep pattern prior to TSD. Clomipramine profoundly suppressed rapid eye movement (REM) sleep; the amount of initial REM sleep reduction, however, did not correlate significantly with therapy response after 3 weeks of treatment.

Adolescent↗
PubMed1993

Cardiovascular response and seizure duration as determined by electroencephalography during unilateral electroconvulsive therapy.

The effect of pulse unilateral electroconvulsive therapy (ECT) on heart rate, blood pressure and the product of heart rate and systolic blood pressure, an index of myocardial oxygen consumption, was studied during 48 ECT sessions in 7 patients with major depression. Intra-individually, hyperventilation-induced hypocapnia compared with normocapnia markedly augmented the ECT-induced increase in heart rate (47% vs 28%) and the product of heart rate and systolic blood pressure (82% vs 60%). Over all ECT seizures, the maximum and increase in heart rate and the product of heart rate and systolic blood pressure were significantly correlated with seizure duration as determined by electroencephalography. However, significant correlations were only present for the seizures during hypocapnia and not during normocapnia. Combining measures of magnitude and length of ECT-induced tachycardia to motor responses may increase the potential for clinical seizure evaluation.

Adult↗
PubMed1994

Electroencephalography, computed tomography and violence ratings of male patients in a maximum-security mental hospital.

A retrospective study of brain investigations of 372 male patients in a maximum-security mental hospital patients is described. All computed tomography (CT) scan and electroencephalography (EEG) reports were collected and rated blind; patients were subsequently divided into 3 groups according to the violence rating of their pre-admission offending behaviour. The 3 groups were similar in their mean age, psychiatric diagnosis, Wechsler Adult Intelligence Scale score and proportions of patients investigated with EEG and CT. In the most violent group, 20% had focal temporal electrical abnormalities on EEG (slowing and/or sharp waves) and 41% had structural abnormalities localised to temporal lobe on CT (dilated temporal horn and/or reduced size of temporal lobe). The corresponding figures for the least violent group are 2.4% and 6.7% respectively. These results suggest that high violence rating scores are associated with temporal lobe abnormalities on CT and abnormal temporal electrical discharges on EEG.

Adult↗
PubMed1996

Subacute sclerosing panencephalitis and acquired immunodeficiency syndrome: role of electroencephalography and magnetic resonance imaging.

Subacute sclerosing panencephalitis (SSPE) had largely disappeared from the United States because of nearly universal measles vaccination, but it has reemerged in children infected with human immunodeficiency virus (HIV). Two children with SSPE are described. The first was HIV positive and presented with seizures and encephalopathy at the age of 21 months. The second developed myoclonus and dementia at age 4 years; she was not infected with HIV, but her mother had acquired immunodeficiency syndrome. Magnetic resonance imaging findings were nonspecific and could have been compatible with HIV encephalopathy. Electroencephalography was characteristic of SSPE, showing high-voltage, periodic slow-wave complexes and background slowing. The diagnosis of SSPE was confirmed by brain biopsy or high measles antibody titers in the cerebrospinal fluid.

AIDS Dementia Complex↗
PubMed2006

Contributions of principal neocortical neurons to magnetoencephalography and electroencephalography signals.

A realistically shaped three-dimensional single-neuron model was constructed for each of four principal cell types in the neocortex in order to infer their contributions to magnetoencephalography (MEG) and electroencephalography (EEG) signals. For each cell, the soma was stimulated and the resulting intracellular current was used to compute the current dipole Q for the whole cell or separately for the apical and basal dendrites. The magnitude of Q is proportional to the magnetic field and electrical potential far from the neuron. A train of spikes and depolarization shift in an intracellular burst discharge were seen as spikes and an envelope in Q for the layer V and layer II/III pyramidal cells. The stellate cells lacked the envelope. As expected, the pyramidal cells produced a stronger Q than the stellate cells. The spikes produced by the layer V pyramidal cells (n = 4) varied between -0.78 and 2.97 pA m with the majority of the cells showing a current toward the pia (defined as positive). The basal dendrites, however, produced considerable spike currents. The magnitude and direction of dipole moment are in agreement with the distribution of the dendrites. The spikes in Q for the layer V pyramidal cells were produced by the transient sodium conductance and potassium conductance of delayed rectifier type; the conductances distributed along the dendrites were capable of generating spike propagation, which was seen in Q as the tail of a triphasic wave lasting several milliseconds. The envelope was similar in magnitude (-0.41 to -0.90 pA m) across the four layer V pyramidal cells. The spike and envelope for the layer II/III pyramidal cell were 0.47 and -0.29 pA m, respectively; these values agreed well with empirical and theoretical estimates for guinea pig CA3 pyramidal cells. Spikes were stronger for the layer IV spiny stellate (0.27 pA m) than the layer III aspiny stellate cell (0.06 pA m) along their best orientations. The spikes may thus be stronger than has been previously thought. The Q for a population of stellate cells may be weaker than a linear sum of their individual Q values due to their variable dendritic geometry. The burst discharge by pyramidal cells may be detectable with MEG and EEG when 10 000-50 000 cells are synchronously active.

Action Potentials↗
PubMed2000

Lead-field bases for electroencephalography source imaging.

In recent years, significant progress has been made in the area of electroencephalography (EEG) source imaging. Source localization on simple spherical models has become increasingly efficient, with consistently reported accuracy of within 5 mm. In contrast, source localization on realistic head models remains slow, with subcentimeter accuracy being the exception rather than the norm. A primary reason for this discrepancy is that most source imaging techniques are based on lead fields. While the lead field for simplified geometries can be easily computed analytically, an efficient method for computing realistic domain lead fields has, until now, remained elusive. In this paper, we propose two efficient methods for computing realistic EEG lead-field bases: the first is element oriented and the second is node oriented. We compare these two bases, discuss how they can be used to apply recent source imaging methods to realistic models, and report timings for constructing the bases.

Biomedical Engineering↗
PubMed2000

Temporally unconstrained space-time treatment of linear formulations of the inverse problem of electroencephalography.

This paper provides an optimal mechanism for the introduction of temporal constraints into linear imaging formulations of the inverse electroencephalography problem. The method is based on derivation of a "virtual-SVD," an extension of generalized singular value decomposition to the setting of random matrices. Surprisingly, the formalism is superior, in principle, to standard regularization methods even in the absence of known temporal constraints. Investigation of this basic temporally unconstrained setting was undertaken to illustrate the application of the method, and as a necessary first step in its systematic evaluation. Although abstract simulations demonstrate superior accuracy for the virtual-SVD method as compared with standard methods, investigation of a particular realistic simulation involving spatiotemporally distributed temporal lobe interictal spikes indicates that significant improvement in solution estimate quality under temporally unconstrained conditions may be limited to a very narrow range of the signal-to-noise ratio (particularly in the context of a markedly row-deficient transfer matrix). These results underline the prospective importance of investigation of the efficacy and feasibility of application of temporal constraints (such as those resulting from knowledge of the general time series format of epilepsy associated wave forms, evoked potentials, etc.) within the derived formalism.

Biomedical Engineering↗