Although depression is associated with more clinical pain complaints, psychophysical data sometimes point to hypoalgesic alterations. Studying the more reflex-like facial expression of pain in patients with depression may offer a new perspective. Facial and psychophysical responses to nonpainful and painful heat stimuli were studied in 23 patients with major depressive disorder (MDD) and 23 matched control participants. As psychophysical data, pain thresholds, tolerance thresholds, and self-report were assessed. Facial responses were videotaped and subjected offline to Facial Action Coding System analysis. One of the key facial responses of pain, which is a known facial signal of negative affect (contraction of the eyebrows), was significantly increased in MDD patients. Moreover, facial expressions and pain ratings were strongly correlated in MDD patients, whereas these 2 response systems were in line with established findings only weakly related in healthy participants. Pain psychophysics was unaltered in MDD patients compared with healthy control participants. In conclusion, the facial expression of pain in MDD patients indicates rather hyper- than hypoalgesia, with enhanced affective pain processing. Moreover, the linkage between subjective and facial responses was much stronger in MDD patients, which may be due to a reduced influence of social display rules, which normally complicate this relationship.

Perspective: The facial expression of pain in patients with depression indicates stronger affective pain processing and stronger association with self-report than in healthy individuals. (C) 2016 by the American Pain Society