Recent studies have suggested an information-processing bias in social phobia (SP). Little is known about the electrophysiological correlates of anxiety in SP. The aim of the present study was to investigate the quantitative electroencephalogram (EEG) in 25 drug-free patients with SP as compared with age- and sex-matched normal controls and to correlate anxiety and depressive symptoms with EEG data. EEG was recorded under vigilance-controlled and resting conditions. The Spielberger State and Trait Anxiety Scale (STAI) and the Beck Depression Inventory (BDI) were administered to assess anxiety and depression levels. Multivariate analysis of variance revealed significant differences between patients and controls, specifically frontopolarly and right centrally. Statistical analysis demonstrated a decrease in absolute and relative delta, theta power, alpha-adjacent slow-beta and fast beta power and an increase in absolute and relative intermediate beta power, as well as an acceleration of the total centroid and a slowing in beta centroid and its variability. Trait anxiety and depression scores correlated positively with the dominant alpha frequency and the alpha centroid, and negatively with absolute theta and slow alpha power as well as with the centroid of the delta/theta frequency band. In conclusion, EEG mapping in patients with SP revealed significant differences from normal controls suggesting a hyperarousal as a pathogenetic factor of anxiety.
Various studies have demonstrated that clinically defined psychiatric populations show electrophysiological patterns that differ statistically both from each other and from normal controls John et al., 1988, John et al., 1994 and Saletu et al., 1987.
Applying standardized recording and analytic procedures, distinct differences were described between psychiatric populations and normal controls in standardized electroencephalogram (EEG) descriptors, such as absolute and relative power as well as the centroid of delta/theta, alpha and beta activity Herman et al., 1989, Saletu et al., 1990 and Saletu et al., 1996.
In social phobia (SP), only a few investigations have been carried out with EEG mapping (Davidson et al., 2000). While speaking in public, social phobics showed a marked increase in right-sided activation in the anterior temporal prefrontal scalp regions. Generalized anxiety disorder (GAD) patients showed an increase in total power, absolute delta/theta and alpha power and relative alpha power and a decrease in relative beta power, neurophysiologically reflecting hypervigilance (Saletu-Zyhlarz et al., 1997). These changes partly correspond to those observed in another anxiety disorder, agoraphobia (with and without panic disorder), which, however, in contrast to GAD, also exhibited an augmentation of beta activity and an acceleration of the delta/theta and alpha centroids (Saletu, 2002).
During hypnotically induced anxiety and relaxation, normal brain electric activity revealed the strongest difference between EEG source gravity center locations during the two emotional states in the excitatory beta-2 EEG frequency band (18.5–21 Hz). Post-hoc tests showed that the sources were located more to the right during anxiety than during relaxation. Studies using various analytic approaches of brain electric measurements repeatedly suggested that positive emotions are implemented by more left-hemispheric activation, whereas negative emotions involve more right-hemispheric activation (Isotani et al., 2001).
A large number of publications has reported on correlations between EEG frequency bands and behavioural measurements. Slow frequencies are known to be associated with behavioural inhibitory functions during sleep, brain lesion, general anaesthesia and intoxication. Frequencies in the high theta and alpha bands are related to attentional states, automated routine behaviour, and cognitive and memory performance—alpha reduction occurs during activation (interruption for resting) of the recorded brain area. Faster EEG wave frequencies (beta bands, gamma band), reflecting neuronal synchronizations at higher frequencies, are associated with activation/excitation, increased vigilance, perceptual and emotional information processing, and effects of psychostimulants Itil, 1983, Ray and Cole, 1985 and Lopes da Silva, 1991. Frontal theta activity are correlated with anxiety levels (Mizuki et al., 1992). High state anxiety is associated with reduced frontal theta (Nakashima and Sato, 1992).
Thus, the aim of the present study was to investigate differences between SP patients and normal controls in EEG mapping, and to relate EEG findings to anxiety and depression levels. We wanted to specify the beta EEG frequencies; we hypothesized significant differences in beta-power between SP patients and healthy controls (HC).
