Consciousness and arousal effects on emotional face processing as revealed by brain oscillations : a gamma band analysis

It remains an open question whether it is possible to assign a single brain operation or psychological function for facial emotion decoding to a certain type of oscillatory activity. Gamma band activity (GBA) offers an adequate tool for studying cortical activation patterns during emotional face information processing. In the present study brain oscillations were analyzed in response to facial expression of emotions. Specifically, GBA modulation was measured when twenty subjects looked at emotional (angry, fearful, happy, and sad faces) or neutral faces in two different conditions: supraliminal (10 ms) vs subliminal (150 ms) stimulation (100 target-mask pairs for each condition). The results showed that both consciousness and significance of the stimulus in terms of arousal can modulate the power synchronization (ERD decrease) during 150-350 time range: an early oscillatory event showed its peak at about 200 ms post-stimulus. GBA was enhanced by supraliminal more than subliminal elaboration, as well as more by high arousal (anger and fear) than low arousal (happiness and sadness) emotions. Finally a left-posterior dominance for conscious elaboration was found, whereas right hemisphere was discriminant in emotional processing of face in comparison with neutral face.