Dirk Hagemann

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.

Individual differences in anterior EEG asymmetry: methodological problems and solutions

In the last two decades, a substantive body of empirical work investigated the association between individual differences of electroencephalogram (EEG) alpha asymmetry and affective/motivational dispositions. Recent work indicated that several methodological problems persist in this field. The present paper reviews these problems with a focus on the reliability and validity of measures of anterior resting EEG asymmetry, which serve as a proxy for trait-like asymmetries of cortical activity. These issues include the treatment of ocular and muscle artifacts, the choice of the EEG reference, the use of current source density (CSD) measures, the state-trait nature of resting asymmetry, and the treatment of state-like fluctuations of the measures. In addition, the statistical problem of inflated type-I error due to multiple testing is also considered and different approaches to counteract this problem are suggested.

Frequency-encoding Thr17 phospholamban phosphorylation is independent of Ser16 phosphorylation in cardiac myocytes.

Both Ser16 and Thr17 of phospholamban (PLB) are phosphorylated, respectively, by cAMP-dependent protein kinase (PKA) and Ca2+/calmodulin-dependent protein kinase II (CaMKII). PLB phosphorylation relieves cardiac sarcoplasmic reticulum Ca2+ pump from inhibition by PLB. Previous studies have suggested that phosphorylation of Ser16 by PKA is a prerequisite for Thr17 phosphorylation by CaMKII and is essential to the relaxant effect of β-adrenergic stimulation. To determine the role of Thr17 PLB phosphorylation, we investigated the dual-site phosphorylation of PLB in isolated adult rat cardiac myocytes in response to β1-adrenergic stimulation or electrical field stimulation (0.1–3 Hz) or both. A β1-adrenergic agonist, norepinephrine (10−9–10−6 m), in the presence of an α1-adrenergic antagonist, prazosin (10−6 m), selectively increases the PKA-dependent phosphorylation of PLB at Ser16in quiescent myocytes. In contrast, electrical pacing induces an opposite phosphorylation pattern, selectively enhancing the CaMKII-mediated Thr17 PLB phosphorylation in a frequency-dependent manner. When combined, electric stimulation (2 Hz) and β1-adrenergic stimulation lead to dual phosphorylation of PLB and exert a synergistic effect on phosphorylation of Thr17 but not Ser16. Frequency-dependent Thr17 phosphorylation is closely correlated with a decrease in 50% relaxation time (t 50) of cell contraction, which is independent of, but additive to, the relaxant effect of Ser16phosphorylation, resulting in hastened contractile relaxation at high stimulation frequencies. Thus, we conclude that in intact cardiac myocytes, phosphorylation of PLB at Thr17 occurs in the absence of prior Ser16 phosphorylation, and that frequencydependent Thr17 PLB phosphorylation may provide an intrinsic mechanism for cardiac myocytes to adapt to a sudden change of heart rate.

Central and autonomic nervous system integration in emotion.

Emotions involve physiological responses that are regulated by the brain. The present paper reviews the empirical literature on central nervous system (CNS) and autonomic nervous system (ANS) concomitants of emotional states, with a focus on studies that simultaneously assessed CNS and ANS activity. The reviewed data support two primary conclusions: (1) numerous cortical and subcortical regions show co-occurring activity with ANS responses in emotion, and (2) there may be reversed asymmetries on cortical and subcortical levels with respect to CNS/ANS interrelations. These observations are interpreted in terms of a model of neurovisceral integration in emotion, and directions for future research are presented.

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.

Dual site phospholamban phosphorylation and its physiological relevance in the heart

Phospholamban (PLB) plays a primary role in regulating cardiac sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity. Dephosphorylated PLB suppresses the SR Ca(2+) pump activity, whereas phosphorylation of PLB leads to deinhibition. A widely accepted sequential model of dual site PLB phosphorylation states that PKA-dependent phosphorylation of Ser(16) is obligatory to phosphorylation of Thr(17) by Ca(2+)/calmodulin-dependent kinase II, and mainly accounts for beta-adrenergic receptor mediated cardiac relaxation. However, emerging evidence supports independent phosphorylation of Ser(16) and Thr(17) and their independent contributions to cardiac relaxation. Furthermore, concurrent activation of PKA and CaMKII signaling pathways exhibits a robust synergistic effect on phosphorylation of Thr(17), but not of Ser(16). Thus, the synergistic interaction may masquerade as a sequential phosphorylation of Ser(16) and Thr(17) under certain circumstances. Further studies are required to determine the exact process of dual site PLB phosphorylation and its functional roles in healthy and diseased hearts.

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.