Anxiety and oscillatory responses to emotional facial expressions.

In the last decade, event-related potential and functional magnetic resonance imaging studies were very useful in temporal and spatial localization of brain processes involved in the recognition of emotional facial expressions. However, frequency characteristics of the underlying processes have been less studied. Besides, most of the studies did not take into account personality-related individual differences. In this study, effects of explicit and implicit anxiety on the oscillatory dynamics of cortical responses elicited by presentation of angry, neutral, and happy faces were investigated using time-frequency decomposition by means of wavelet transform. Both explicit and implicit anxiety were associated with higher alpha band desynchronization, which was most pronounced during presentation of angry faces. Within theta and delta bands, effects appeared to be opposite for explicit and implicit anxiety measures. In implicitly anxious subjects, frontal delta and theta synchronization upon the presentation of angry and happy (but not neutral) faces was found to be higher than in low anxiety ones, whereas explicit anxiety was associated with a lower theta band synchronization. The results are discussed in terms of conscious and controlled vs. unconscious and intuitive information processing associated with explicit and implicit personality measures.

Impulsivity, anxiety, and individual differences in evoked and induced brain oscillations.

There is much evidence to confirm the view that slow waves of delta and theta ranges are linked to activation whereas alpha oscillations are somehow related to inhibition processes. In the domain of individual differences, impulsive behavior is frequently associated with increased spectral power of slow oscillations whereas Behavioral Inhibition (BI) may be associated with higher reactivity within alpha band. Here it is hypothesized that Impulsivity would predispose to higher responding in low frequencies whereas BI would predispose to higher responding within alpha band. In a sample of 51 subjects, evoked and induced responses to auditory stimuli were studied in two experimental sessions: 1) in a simple discrimination task and 2) in a stop-signal task in which subjects had to be ready to withdraw the prepared motor response. Impulsive subjects showed higher baseline delta, theta and alpha power and higher magnitude of induced responses in low frequencies. They also showed lower phase-locking in low frequencies to auditory stimuli and higher phase-locking to the overt behavioral response onset. High BI scorers showed higher baseline alpha power and higher desynchronization in this frequency band in response to stimuli. The reported findings appear to support the idea that low frequency oscillations are associated with behavioral approach and alpha with behavioral inhibition tendencies but these associations are only valid for induced responses to stimuli.

A failure to stop and attention fluctuations: an evoked oscillations study of the stop-signal paradigm.

OBJECTIVE: It is not always clear whether inhibition or attention deficit underlies a failure to stop a prepared motor response. One possible way to approach this question is to resort to measures of evoked oscillations since functional correlates of different frequency oscillations are relatively well understood. METHODS: The present study examined event-related oscillations during a stop-signal task in non-clinical adults. In 25% of trials of an auditory discrimination tasks subjects had to refrain from a prepared motor response. RESULTS: In successful stop trials, the Go N2 peaked later and the Stop N2 peaked earlier than in failed stop trials. Relative to successful, failed stop trials were associated with a larger N1-N2 and Go P3, and a smaller Stop P3 in the central and posterior cortical regions. The latter effect was exclusively determined by evoked delta oscillations, whereas all other frequency bands contributed to enhanced responses in failed comparative to successful stop trials. CONCLUSIONS: The sum of presented evidence seems to show that success or failure to stop mostly depends on how the subject prepares for the Go and Stop stimuli in advance. If attention is more directed towards the Stop signal, the stopping succeeds, otherwise it fails. SIGNIFICANCE: These data may contribute to understanding the cognitive basis of successful and unsuccessful stopping performance.

Alpha synchronization and anxiety: implications for inhibition vs. alertness hypotheses.

Although there is much evidence that alpha oscillations are linked with processes of perception, attention and semantic memory, their functional significance remains uncertain. Synchronization in the alpha frequency range is taken to be a marker of cognitive inactivity, active inhibition of sensory information, or a means of inhibition of non-task relevant cortical areas. Here we propose an alternative interpretation which posits that higher alpha power during reference interval signifies higher readiness of alpha system to information processing. Predictions derived from the inhibition and alertness hypotheses were tested during presentation of acoustic stimuli (tone 1000 Hz) and neutral words to 30 males (18-25 years) with different levels of trait anxiety. On the whole, predictions derived from the inhibition theory were not confirmed and findings more corresponded to the alertness hypothesis. High-anxiety subjects showed higher alpha power during reference interval simultaneously with higher magnitude of event-related desynchronization and higher amplitude of phase-locked alpha responses. These findings are discussed in terms of functional significance of alpha band synchronization and desynchronization.

Anxiety and synchrony of alpha oscillations.

The associations between state anxiety and individually adjusted alpha sub-bands mean spectral power and coherence measures registered in resting condition and during experimental settings were investigated in 30 males aged 18-25 years. Averaged across all cortical sites, spectral power was treated as a complex measure dependent on both the number of active alpha oscillators and the degree of their synchrony. Averaged across all electrode pairs, squared coherence was treated as a global measure of alpha synchrony. The relationship between state anxiety and baseline alpha power was mostly mediated by alpha synchrony. During transition through experimental settings, the dynamics of alpha2 and alpha3 power was mostly accounted for by changes of these sub-bands' synchrony. The synchrony-independent power component demonstrated linear trends implying that, during the experiment, the number of active alpha oscillators linearly decreased in subjects with low state anxiety and linearly increased in subjects with high state anxiety. These findings are discussed in terms of alpha synchronization as an active process, allowing dynamic regulation of alpha system preparedness for processing of external stimuli.

Uncertainty, anxiety, and brain oscillations.

Influence of anxious expectation on spectral power and delta-gamma coupling was studied in 39 subjects (27 females) aged 19-30 years who also filled out the State Trait Anxiety Inventory. The situation of uncertainty was associated with general increase in spectral power of all EEG bands, which was particularly pronounced in high-trait anxiety subjects. In low-trait anxiety subjects, association between delta and gamma power significantly increased when they had to expect bad news but did not change when they expected good news. In high-trait anxiety subjects, this association tended to increase in both cases. Higher baseline delta power predicted higher gamma power in the situation where a bad news was expected. These findings are discussed in terms of Gray and McNaughton's theory of anxiety and evolutionary interpretation linking delta oscillations with reward motivation. Increase of delta-gamma coupling in anxiogenic situation is interpreted to reflect higher cortical arousal, which appears in a frustrating situation in subjects with higher activity of "motivational" delta system.

Alpha oscillations as a correlate of trait anxiety.

The associations among psychometric measures of anxiety and depression and individually adjusted electroencephalogram (EEG) spectral power measures registered in resting condition and during experimental settings were investigated in 30 males aged 18-25 years. During all stages of registration, Taylor Manifest Anxiety and Spielberger state anxiety (SA) and trait anxiety (TA) scores were positively related to alpha and negatively to delta relative power with these relations being independent of cortical site. Within-subject estimate of the strength of reciprocal relationship between alpha and delta oscillations (alpha-delta anticorrelation, or ADA) was positively related to trait anxiety and depression. Three minutes after an alarming event (unexpected loud sound), a further increase of alpha power was observed. In low-anxiety subjects, this increase was mostly associated with fast alpha (alpha 3), whereas in high-anxiety ones, it was mainly linked to slow alpha (alpha 2). SA mediated relationship between TA and EEG power, while ADA and alpha band reactivity showed trait-like features being associated with TA even after accounting for SA. These findings are interpreted as an indication of higher vigilance and higher reactivity of alpha system in anxious individuals.