Abstract
The prefrontal cortex plays a key role in emotional state. Electroencephalography (EEG) studies have reported relationships between frontal asymmetry in the alpha band, emotional state, and emotion-related motivation. The current study investigated whether the positive or negative valence of emotional stimulation or the behavioral intention to either facilitate or suppress one’s facial expression in response to these stimuli is reflected in relevant changes in frontal EEG asymmetry. EEG was recorded while participants either produced a facial expression that was in accord with positive or negative feelings corresponding to image stimuli, or suppressed their facial expressions. The laterality index of frontal alpha power indicated greater relative right frontal activity while participants suppressed facial expression compared with facilitating facial expression during emotional stimulation. However, there was no difference in frontal asymmetry between the presentation of image stimuli showing facial expressions corresponding to positive vs. negative emotions. These results suggested that frontal asymmetry was related to the control of facial emotional expressions rather than the perception of positive vs. negative emotions. Moreover, microstate analysis revealed that the appearance rate of microstate class B with polarity in the left frontal area increased during the suppression of facial expressions. The present results suggested that frontal asymmetry reflects the control of facial emotional expressions, which supports the motivational direction model.
Highlights
In recent years, with technological progress in machine learning and measurement instruments, new techniques for estimating emotion have been developed
Based on the two models discussed above, we sought to test the following two hypotheses: (1) if PFC asymmetry reflects the perception of positive and negative emotional states, based on the affective valence model, relatively greater activity of the left compared with right PFC would be expected following stimulation with positive compared with negative images; and (2) if PFC asymmetry reflects the control of facial emotional expressions of facilitation and suppression, based on the motivational direction model, relatively greater activity of right than left PFC would be expected following emotional stimulation with instructions to suppress emotional expressions, regardless of the valence of the emotional stimuli
Post hoc testing revealed that the scores for negative images were significantly higher than those for positive (p < 0.05) or neutral (p < 0.001) images
Summary
With technological progress in machine learning and measurement instruments, new techniques for estimating emotion have been developed. Psychophysiological studies estimating emotion are employed in various fields, such as neuromarketing and the development of communication tools for people with physical disabilities. To examine the neural mechanisms of emotion, brain function imaging devices such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) have been widely used to measure whole brain activity. Electroencephalography (EEG) has been used in psychophysiological studies because EEG measurement involves a relatively small burden for participants. EEG has high temporal resolution and, with the development of analytical technology, is capable of examining cortical neuronal networks. The relationship between frontal EEG asymmetry and emotional state has been investigated for a relatively long time
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