Processing emotions in children with Moebius syndrome. A behavioral and thermal imaging study

According to the “facial feedback hypothesis”, the proprioceptive feedback from facial muscles while mimicking face movements is crucial in regulating emotional experience. Facial mimicry, intended as a spontaneous reaction of individuals when observing emotional faces, plays a key role in understanding others’ facial expression of emotions. Studies on facial expression processing and emotion understanding have revealed that the neuronal bases of facial mimicry are underpinned by a mirror mechanism, named “mirror neuron system” (MNS), which is active during both observation and imitation of facial expressions. The emotion recognition process is therefore based on the activation in the observer of a neural motor representation similar to that present in the observed one. In addition to this, a tight connection between motor and autonomic responses has been proposed. Neuroimaging studies, in fact, showed that the observation and first-person experience of an emotional state involve a more widespread network composed of the anterior insula, the anterior cingulate cortex and the amygdala, whose functions are strictly associated with the processing of the emotional valence of stimuli and to visceromotor responses to emotions. Individuals with deficits in the motor programs involved in expressing emotions could therefore be impaired in the face-based recognition process or, according to simulation theories, in responding to emotional stimuli through the activation of similar somatomotor and visceromotor responses. In this regard, Moebius syndrome (MBS) patients represent an optimal model to test this hypothesis. MBS is a rare congenital neurological disorder affecting the VI and VII cranial nerves, resulting in facial paralysis. MBS patients are therefore unable to perform any sort of facial movement, or, depending on the severity of the damage, have extensive deficits in the motor control of facial muscles. The aim of this doctoral thesis was to investigate emotional processing in MBS children. Physiological measurements were performed by means of a functional infrared thermal imaging (fIRT), a dynamic, contactless, non-invasive method that allows to map bodies’ skin temperature distribution in order to quantify autonomic nervous system (ANS) responses to emotional stimuli. The first study highlighted that MBS children (mean age = 5.5) display lower scores of emotion recognition and exhibit a weaker thermal response to emotional (video cartoon) stimuli than healthy children of comparable age. The second study showed that children with MBS (mean age = 9.0) do not show differences in response times on emotion recognition, however they perform a higher number of errors in labelling the facial expressions than age and gender matched controls. The third study confirmed that MBS children (mean age = 8.7) have difficulties in categorizing emotions presented as dynamic facial expressions, and revealed that, unlike controls, they are characterized by a lower thermal response to emotional faces than to neutral faces. Overall, these findings support embodied simulation theories, according to which the motor control of the facial musculature and the facial peripheral feedback are critical for emotional expression recognition. In addition, impairments of facial movements can attenuate the intensity of emotional experience both when stimuli represent a more general emotional context, as the one depicted by animated video cartoons, and when a more specific type of stimuli (i.e. faces displaying different emotions) is presented. The differences in thermal responses between MBS patients and controls are probably ascribed to a differential and diminished activation of the autonomic responses associated to emotions.