Resting posterior versus frontal delta/theta EEG activity is associated with extraversion and the COMT VALMET polymorphism

Recent studies suggest that resting posterior versus frontal EEG delta/theta activity (delta/theta Pz–Fz) is both sensitive to pharmacological manipulations of neural dopamine and associated with the agency facet of extraversion (i.e., a motivational disposition comprising enthusiasm, energy, assertiveness, achievement striving and social dominance). These observations suggest that posterior versus frontal resting EEG delta/theta activity may represent a useful marker for investigating the molecular genetic basis of extraversion. The present study aimed to test the novel hypothesis of an association between delta/theta Pz–Fz and a functional polymorphism of the enzyme catechol-O-methyltransferase (COMT VAL¹⁵⁸MET) involved in dopamine catabolism. This was conducted in a large EEG data set from the Brain Resource International Database (BRID; resting EEG from N = 1093 healthy individuals, 382 of which also genotyped for COMT VAL¹⁵⁸MET). In summary, we (1) showed for the first time that the VAL allele is associated with increased delta/theta Pz–Fz; (2) replicated the association between extraversion and delta/theta Pz–Fz in a large, heterogeneous sample including both genders; and (3) documented that the VAL allele of the COMT VAL¹⁵⁸MET is associated with increased extraversion scores, as previously reported for an overlapping BRID sample. This coherent pattern of findings adds further support to the suggestion that the posterior–anterior distribution of resting EEG slow wave activity in the delta/theta range represents a useful tool for probing the dopaminergic basis of extraversion.     

Spontaneous and MNNG‐induced reversion of an EGFP construct in HeLa cells: An assay for observing mutations in living cells by fluorescent microscopy

A HeLa cell line stably expressing the enhanced green fluorescence protein (EGFP) gene, interrupted by the HBB IVS2‐654 intron, was studied without treatment and after treatment with a single standard dose of 15 μM of N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG). This assay was done in order to prove that such a construct can revert by a variety of mechanisms and that it produces a visible phenotype, i.e., green fluorescence. The system permits visual detection of living mutant cells among a background of non‐mutant cells and does not require a selective medium. The results show that the construct reverts by large deletions (–62, –100, and –162 bp), small insertions (+4 bp), small rearrangements (19 bp duplication), base substitutions at purines (G₆₅₂, G₆₅₃, A₆₅₅, G₅₇₉), and a pyrimidine (T₆₅₄) between nucleotide positions 579 and 837. Splice‐site mutations were recovered, and some of the mechanisms underlying these mutations are discussed. Because of the ease of detection of revertant cells under fluorescent light and the wide variety of mutations that can be recovered, further development of this system could make it a useful new mammalian cell mutagenicity assay. Hum Mutat 18:526–534, 2001. © 2001 Wiley‐Liss, Inc.     

Finite-element model of the human head: scalp potentials due to dipole sources

Three-dimensional finite-element models provide a method to study the relationship between human scalp potentials and neural current sources inside the brain. A new formulation of dipole-like current sources is developed here. Finiteelement analyses based on this formulation are carried out for both a threeconcentric-spheres model and a human-head model. Differences in calculated scalp potentials between these two models are studied in the context of the forward and inverse problems in EEG. The effects of the eye orbit structure on surface potential distribution are also studied.     

EEG versus MEG localization accuracy: Theory and experiment

Summary We first review the theoretical and computer modelling studies concerning localization accuracy of EEG and MEG, both separately and together; the source is here a dipole. The results show that, of the three causes of localization errors, noise and head modelling errors have about the same effect on EEG and MEG localization accuracies, while the results for measurement placement errors are inconclusive. Thus, these results to date show no significant superiority of MEG over EEG localization accuracy. Secondly, we review the experimental findings, where there are again localization accuracy studies of EEG and MEG both separately and together. The most significant EEG-only study was due to dipoles implanted in the heads of patients, and produced an average localization error of 20 mm. Various MEG-only studies gave an average error of 2–3 mm in saline spheres and 4–8 mm in saline-filled skulls. In the one study where EEG and MEG localization were directly compared in the same actual head, again using dipoles implanted in patients, the average EEG and MEG errors of localization were 10 and 8 mm respectively. The MEG error was later confirmed by a similar (but MEG-only) experiment in another study, using a more elaborate MEG system. In summary, both theory and experiment suggests that the MEG offers no significant advantage over the EEG in the task of localizing a dipole source. The main use of the MEG, therefore, should be based on the proven feature that the MEG signal from a radial source is highly suppressed, allowing it to complement the EEG in selecting between competing source configurations. A secondary useful feature is that it handles source modelling errors differently than does the EEG, allowing it to help clarify non-dipolar extended sources.This work was supported by grants RO1NS26433, RO1NS19558 and RO1NS22703 from the National Institutes of Health.     

Accurate Matching of electromagnetic dipole data with CT and MR images

Interpretation of EEG (electroencephalography) or MEG (magnetoencephalography) derived three-dimensional dipole localizations is hampered by poor visualization. This paper describes a method for combining dipole data with structural image data of the same patient. To ensure high precision this method utilizes external markers that are easy to apply. These markers can achieve subslice accuracy and can even be used to pinpoint reference points outside the scanned volume. Accurate matching is thus provided even in standard imaging protocols employing thick slices and/or large interslice gaps. The results of the matching method are presented in 2D and 3D visualizations. The hybrid images facilitate the interpretation of dipole localizations with respect to the patient's anatomy.     

The value of EEG-Mapping in focal cerebral lesions

Summary In 148 patients with focal cerebral lesions the findings of EEG mapping, routine EEG and CT were compared. Regarding etiology 43 patients suffered from completed stroke (CS), 43 patients from transient ischemic attack (TIA), 33 patients had an intracerebral hemorrhage (ICH) and 29 an hemispheric tumor. In 37 patients with CS (86%) and 27 patients with TIA (63%) the EEG mapping revealed focal changes, but only in 28 patients with CS (65%) and in 11 patients (26%) with TIA using routine EEG alone. Thus the EEG mapping showed focal abnormalities significantly more often. In the remaining patient groups no significant difference in the results of EEG mapping or routine EEG could be demonstrated. Focal abnormalities corresponding to focal lesions seen in CT were obtained by means of EEG mapping in 27 patients (90%) with CS and 10 patients (77%) with TIA, but only in 17 patients (57%) with CS and 4 patients (31%) with TIA using routine EEG and in that way the EEG mapping could indicate focal lesions in CT significantly more often than routine EEG. In the remaining patient groups no significant difference in the number of focal changes corresponding to lesions in CT could be seen.     

Wirkungen von Cyclandelat auf das ZNS — Eine doppelblinde,placebo-kontrollierte Studie an gesunden Probanden

Summary The effect of cyclandelate (Natil^®) on the CNS was tested in a double-blind, placebocontrolled pilot study on 48 healthy males using a single oral dosage of 1200 mg. The EEG was evaluated quantitatively by spectral analysis before and one hour as well as two and a half hours after drug or placebo administration under resting conditions and while performing a test of mental arithmetics. Under resting conditions the power in the alpha₂ frequency band of the signals from the frontal and central recordings was increased in the cyclandelate group in comparison to the placebo group. This effect was still observed two and a half hours after drug intake.Under the condition of mental arithmetics no drug related effect was observed in the EEG. The cyclandelate induced increase of spectral power in the alpha₂ frequency band under resting conditions demonstrates a general effect of cyclandelate on the CNS. The results are discussed with respect to the known age related decrease of spectral power in the alpha frequency band. The established effect of cyclandelate in young healthy subjects calls for a study with chronic treatment in elderly subjects or patients with cognitive deficits.

     

Statistically comparing EEG/MEG waveforms through successive significant univariate tests: How bad can it be?

When making statistical comparisons, the temporal dimension of the EEG signal introduces problems. Guthrie and Buchwald (1991) proposed a formally correct statistical approach that deals with these problems: comparing waveforms by counting the number of successive significant univariate tests and then contrasting this number to a well‐chosen critical value. However, in the literature, this method is often used inappropriately. Using real EEG data and Monte Carlo simulations, we examined the problems associated with the incorrect use of this approach under circumstances often encountered in the literature. Our results show inflated false‐positive or false‐negative rates depending on parameters of the data, including filtering. Our findings suggest that most applications of this method result in an inappropriate familywise error rate control. Solutions and alternative methods are discussed.     

Does response selection contribute to inhibition of return?

Inhibition of return (IOR) means delayed responses for targets at a cued compared to targets at an uncued location. It is assumed to reflect delayed reallocation of attention toward a previously attended location. Besides an attentional mechanism, IOR could also be due to a cue‐evoked inhibition to respond toward a cued target. In the present study, IOR with simple, compatible, and incompatible choice responses was compared and tracked by means of event‐related EEG activity. IOR was amplified with simple responses but did not differ between compatible and incompatible responses. Attention‐related ERP correlates were constant across cue target onset asynchronies as were, in part, behavioral effects. Early, rather sensory ERP components varied with time, reflecting sensory or attentional interaction of cue and target processing. None of these effects varied with response requirements, indicating that response selection does not contribute to IOR in manual choice response tasks.