Congenital facial palsy and emotion processing: The case of Moebius syndrome

According to the Darwinian perspective, facial expressions of emotions evolved to quickly communicate emotional states and would serve adaptive functions that promote social interactions. Embodied cognition theories suggest that we understand others' emotions by reproducing the perceived expression in our own facial musculature (facial mimicry) and the mere observation of a facial expression can evoke the corresponding emotion in the perceivers. Consequently, the inability to form facial expressions would affect the experience of emotional understanding. In this review, we aimed at providing account on the link between the lack of emotion production and the mechanisms of emotion processing. We address this issue by taking into account Moebius syndrome, a rare neurological disorder that primarily affects the muscles controlling facial expressions. Individuals with Moebius syndrome are born with facial paralysis and inability to form facial expressions. This makes them the ideal population to study whether facial mimicry is necessary for emotion understanding. Here, we discuss behavioral ambiguous/mixed results on emotion recognition deficits in Moebius syndrome suggesting the need to investigate further aspects of emotional processing such as the physiological responses associated with the emotional experience during developmental age. (A) Facial imitation therapy ‐ sinergistic activity therapy (FIT‐SAT) treatment. Each session starts with a video‐clip in which an actor remains still for 3 seconds and vocal instruction are given to the patients. Then the actor performs a smile either unilaterally (left or right side) or bilaterally. The patients are instructed to observe the video‐clip and simultaneously imitate the actor's smile. While they are smiling, the patients simultaneously clench their fist. Patients start the daily treatment with three sets of five repetitions. Progressively, further repetitions are gradually included until the patient is able to perform at least 10 successive repetitions and to maintain the smile posture for at least 3 seconds. (B) FIT combined action observation with the direct effects of action execution suggesting that the activation of motor areas by action observation becomes reinforced by the concomitant active execution of the observed actions; SAT refers to the synergistic activity of hand closing while smiling should facilitate the activation of the cortical areas connected to the mouth. The hand contraction facilitates