Temporal dissociation in the brain processing of pain and anger faces with different intensities of emotional expression.

Facial expression is one of the most relevant nonverbal behaviors in the communication of pain. However, little is known about brain processing of pain expressions in comparison with other affective facial expressions. The present experiment aimed to examine the effects of pain expression intensity on affective ratings and brain dynamics by recording electroencephalography (EEG) from 20 female healthy volunteers 18-24 years of age. Participants were asked to rate the affective characteristics of 144 stimuli depicting facial expressions of pain and anger with 3 level of intensities (high, mild, and low), as well as neutral faces. Results indicated that pain faces were judged as more unpleasant and arousing than anger and neutral faces for all intensity levels. EEG results further showed that facial expressions of pain elicited more enhanced amplitudes of the visual evoked potentials than anger and neutral faces in the latency between 350 and 550 milliseconds after stimulus onset; whereas anger faces elicited greater P200 amplitudes than pain and neutral faces. In addition, more increased theta activity in the latency of 200 to 400 milliseconds after stimulus onset was observed to high-intense as compared with low-intense facial expressions. These findings indicate that brain activity elicited by affective faces is modulated by the intensity of facial expressions and suggest the involvement of different brain mechanisms during the processing and recognition of facial expressions of pain and anger in healthy volunteers.