Ewald Naumann

The quest for the EEG reference revisited: A glance from brain asymmetry research

Recent findings suggested that the choice of the EEG reference might be a critical issue for the study of anterior asymmetry in the alpha band. The present paper investigates the validity of different reference schemes for the measurement of alpha asymmetry. A 32-channel resting EEG was recorded with a common vertex reference (Cz), and transformed into computer-averaged ears (A1 + A2), average reference (AR), and current source density derivations. A correlation analysis of an alpha asymmetry measure between all derivation schemes indicated a poor convergent validity for anterior sites but an excellent convergent validity for posterior sites. Further analyses suggested the presence of substantial alpha activity at the various reference sites (Cz, A1 + A2, AR), which might be similar in magnitude to anterior but smaller than posterior alpha. These findings suggest that the validity of a reference scheme is a function of the signal-to-noise ratio of the electrical activities at target and reference sites. The limitations of each reference scheme for the measurement of anterior alpha asymmetry are discussed.

Does resting electroencephalograph asymmetry reflect a trait? an application of latent state-trait theory.

Recent research on brain asymmetry and emotion treated measures of resting electroencephalograph (EEG) asymmetry as genuine trait variables, but inconsistency in reported findings and modest retest correlations of baseline asymmetry are not consistent with this practice. The present study examined the alternative hypothesis that resting EEG asymmetry represents a superimposition of a traitlike activation asymmetry with substantial state-dependent fluctuations. Resting EEG was collected from 59 participants on 4 occasions of measurement, and data were analyzed in terms of latent state-trait theory. For most scalp regions, about 60% of the variance of the asymmetry measure was due to individual differences on a temporally stable latent trait, and 40% of the variance was due to occasion-specific fluctuations, but measurement errors were negligible. Further analyses indicated that these fluctuations might be efficiently reduced by aggregation across several occasions.

On the selective relation of frontal cortical asymmetry and anger-out versus anger-control.

The model of anterior asymmetry and emotion proposes an asymmetric representation of approach and withdrawal systems in the left and right anterior brain regions. Within this framework, 3 different concepts have been related to anterior asymmetry: affective valence, motivational direction, and behavioral activation. The aim of the present study was an empirical investigation into the relation between anterior cortical activity and questionnaire measures related to the 3 dimensions positive versus negative affect, approach versus withdrawal motivation, and behavioral activation versus inhibition. Subjects with relative greater left than right frontal cortical activity showed higher anger-out scores and lower anger-control scores. These results support the hypothesis that motivational direction is related to frontal asymmetry (approach-left and withdrawal-right). Furthermore, subjects with greater bilateral (left and right) frontal cortical activity showed higher behavioral activation scores. This finding might suggest that behavioral activation is related to approach and withdrawal motivation.

The effects of ocular artifacts on (lateralized) broadband power in the EEG

OBJECTIVE Empirical evidence suggests that blinks and eye movements do not generate substantial activity outside the delta and theta range, and that the propagation of ocular activity to the EEG is rather symmetrical. These observations suggest that an alteration of the alpha and beta asymmetry of the EEG due to ocular artifacts is not likely to occur. The aim of the present study is to examine the effects of ocular artifacts on broadband EEG parameters. METHODS EEG and EOG were recorded from 31 participants in a resting condition with eyes open and closed, allowing for spontaneous ocular activity. General effects of ocular artifacts were examined with mean comparisons, and differential effects were examined with correlation analysis of data portions that were selected for a presence or absence of artifacts. RESULTS At single sites, blinks and eye movements exerted substantial general effects on the whole EEG spectrum, but there were no substantial differential effects of artifacts in the alpha and beta bands, except at the frontopolar sites. The distorting effects of ocular artifacts were smaller in magnitude for asymmetry than for single site measures. CONCLUSIONS The control of ocular artifacts may be dispensable for correlation analyses of alpha or beta band parameters.

The assessment of affective reactivity using films : Validity, reliability and sex differences

Abstract Researchers interested in individual differences of brain asymmetry and affective reactivity have recently used film clips to elicit emotions and provided some standardisation data of emotion ratings for English-speaking samples. The aim of the present study was to examine whether (1) a set of films which already proved to elicit different emotions in English-speaking samples would demonstrate a similar capacity to induce emotions in a German sample and (2) to explore the validity, reliability and sex differences of aggregated indices of affective reactivity. Based on two film sets which have been examined by other investigators in the field, we formed a set of 13 emotion-eliciting films and presented the films along with emotion rating scales to university students. Our findings indicate that most films had the capacity to elicit specific discrete target emotions and the emotions elicited by the negative clips were more distinct than the emotions due to the positive clips. The factor structure of the emotion rating scales indicated that a distinct positive and negative dimension was extracted. The indices of positive and negative affective reactivity demonstrated good reliability and internal consistency. Women reported on greater levels of affective reactivity than men, both for positive and negative affective reactivity.

The relation of cortical activity and BIS/BAS on the trait level.

The behavioral activation system (BAS) and the behavioral inhibition system (BIS) have been proposed to be related to anterior asymmetry in the BIS/BAS model of anterior asymmetry. As an alternative, it may be suggested that behavioral activation comprises approach and withdrawal motivation and that the BAS is related to bilateral frontal trait activity. The aim of the present study was an empirical investigation on the relation between cortical trait activity, BIS and BAS. Data of 59 subjects on four occasions were analyzed. On each occasion, cortical activity was evaluated with resting EEG, and the BIS and BAS strength was assessed with questionnaires. Subjects with greater bilateral frontal cortical activity showed higher BAS scores. The latter result may suggest that behavioral activation comprises approach and withdrawal motivation.

EEG asymmetry, dispositional mood and personality

Abstract Recent studies have demonstrated that dispositional positive affect (PA) and negative affect (NA) can be predicted by resting electroencephalographic (EEG) asymmetry in anterior brain regions. The aim of the present study was a conceptual replication of these results. An extensive literature review suggested that asymmetry might also be related to personality and we investigated the possibility to extend the association between asymmetry and dispositional mood to personality traits. Resting EEG of 36 subjects was recorded and questionnaires were administered to assess PA, NA, extraversion (E) and neuroticism (N). Subjects who scored high on NA had greater relative left-sided cortical activation than subjects scoring low on NA, which was due to greater absolute activation of the left anterior temporal site in high NA scorers. There were no associations between asymmetry and PA. A functional neuroanatomical model is presented which suggests that greater tonical activation of the left temporal cortex increases the susceptibility to experience negative emotions.

Resting cerebral blood flow, attention, and aging.

Aging is accompanied by a decline of fluid cognitive functions, e.g., a slowing of information processing, working memory, and division of attention. This is at least partly due to structural and functional changes in the aging brain. Although a decrement of resting cerebral blood flow (CBF) has been positively associated with cognitive functions in patients with brain diseases, studies with healthy participants have revealed inconsistent results. Therefore, we investigated the relation between resting cerebral blood flow and cognitive functions (tonic and phasic alertness, selective and divided attention) in two samples of healthy young and older participants. We found higher resting CBF and better cognitive performances in the young than in the older sample. In addition, resting CBF was inversely correlated with selective attention in the young and with tonic alertness in the elderly participants. This finding is discussed with regard to the neural efficiency hypothesis of human intelligence.

Stability of heart rate variability indices reflecting parasympathetic activity

Heart rate variability (HRV) is a measure of autonomic influences on heart rate that has frequently been used as a transsituationally consistent biomarker for cardiovascular health and emotional or cognitive functions. The psychometric properties of HRV however remain unclear. In the present study, we examined the reliability and temporal stability of parasympathetic HRV measures and estimated the portion of variance explained by transsituationally consistent trait variance and by effects of the situation and person-situation interaction with structural equation modeling. The results show good reliability of indices reflecting central parasympathetic control over heart rate and that about 40% of the variance of a single HRV measurement can be explained by effects of the situation and person-situation interaction. An aggregation across at least two measurements may be recommended when using HRV as a transsituationally consistent biomarker or trait.

The scalp topography of P300 in the visual and auditory modalities: a comparison of three normalization methods and the control of statistical type II error

This study was designed to replicate recent findings suggesting that the P3 component of the event-related potential is dependent on the modality of the eliciting stimulus. When assessing this research hypothesis two methodological problems are of special interest: first, the amplitudes have to be normalized, due to problems with the model of the analysis of variance; second, special care has to be taken regarding the beta error, which is the probability of falsely accepting the null hypothesis of a statistical test. A possible modality independence is associated with the acceptance of a null hypothesis. The first problem was assessed by using different normalization procedures and comparing their results. The second was solved by controlling the beta error. Results for P3 amplitudes from two sessions in which 61 subjects performed in each session an auditory and a visual oddball task (EEG measured at 11 locations) showed no influence of modality on the P3 elicited by the rare, task relevant, stimulus. Influences of modality were observed for the P3 elicited by the frequent stimulus. As it is quite unlikely that P3 generating sources are strongly active during the processing of the frequent stimulus, this effect is possibly due to a component overlap from the vertex potential.