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.

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 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.

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.

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