## Appendix B Facial Emotion Recognition  
[PERSON], an American anthropologist and psychologist known for his research on non-verbal communication, described six basic emotions expressed through the face. These six emotions--sad, happy, disgust, anger, fear, and surprised--are independent of gender, age, and culture and are very important for the so-called facial reflex in non-verbal communication [104]. In addition to correlating with alexithymia, facial emotion recognition (FER) is impaired in people with chronic facial pain, somatoform disorders, and low back pain [12; 58; 59; 105]. The FER examination works through special visual programs in which people see a series of pictures of faces with the described emotional expressions. They then must accurately name the emotion shown at a given time.  
Psychiatric disorders or impairments with a psychiatric background have already been extensively investigated for possible abnormalities in facial emotion recognition. Studies on anorexia nervosa, depression, somatoform disorders, substance abuse, anxiety, and panic disorders, as well as studies on the autism spectrum, show tendencies towards abnormalities, but reliable and reproducible data are lacking [58; 60; 61; 106; 107; 108]. Studies do support the hypothesis that alexithymia may be responsible for the deficits in FER that occur in some clinical disorders. However, the literature also shows that impairments in processing FER that occur in association with high levels of alexithymia may be partly due to depression and anxiety. Furthermore, behavioral and neuroimaging studies suggest that alexithymia is already associated with processing deficits at the perceptual level. More specifically, FER processing may be particularly impaired in the context of severe alexithymia when test images are presented very briefly and/or when images are of poor quality. Downgraded semantic representations of emotional concepts could also be responsible for the deficits in processing FER in severe alexithymia [74].  
In the spectrum of neurological diseases such as stroke, Parkinson's disease, and other neurodegenerative diseases, studies on FER also show trends towards impairment, which could justify both screenings for and treatment of these deficits [51; 62; 75; 109]. Facial emotion recognition has not yet been studied in the context of chronic migraine. However, the work of [PERSON] et al. (2015) showed poorer performance in patients with episodic migraine in both face recognition and visuospatial perception. The authors attributed these results to functional differences in the brains of those affected or to genetic changes [110].  
In a functional magnetic resonance imaging (fMRI) study, subjects suffering from episodic migraine showed increased neural activation, primarily in response to fearful faces compared to neutral faces in the right-middle frontal gyrus and frontal area compared to healthy controls. In addition, higher migraine attack frequency was found to be associated with increased activation, primarily in the right primary somatosensory cortex (corresponding to the facial area) for fearful expressions and in the right dorsal striatal regions for happy faces. In both analyses, activation differences remained significant, even after controlling for anxiety and depressive symptoms. These results suggest that an enhanced response to emotional stimuli may explain the migraine-triggering effect of psychosocial stressors, which gradually leads to an enhanced somatosensory response to emotional stimuli and, thus, contributes to the progression or chronification of migraine [111].