The mirror neuron network (MNN) has been proposed as a neural substrate of action understanding. Electroencephalography (EEG) mu suppression has commonly been studied as an index of MNN activity during execution and observation of hand and finger movements. However, in order to establish its role in higher order processes, such as recognizing and sharing emotions, more research using social emotional stimuli is needed. The current study aims to contribute to our understanding of the sensitivity of mu suppression to facial expressions. Modulation of the mu and occipital alpha (8–13 Hz) rhythms was calculated in 22 participants while they observed dynamic video stimuli, including emotional (happy and sad) and neutral (mouth opening) facial expressions, and non-biological stimulus (kaleidoscope pattern). Across the four types of stimuli, only the neutral face was associated with a significantly stronger mu suppression than the non-biological stimulus. Occipital alpha suppression was significantly greater in the non-biological stimulus than all the face conditions. Source estimation standardized low resolution electromagnetic tomography (sLORETA) analysis comparing the neural sources of mu/alpha modulation between neutral face and non-biological stimulus showed more suppression in the central regions, including the supplementary motor and somatosensory areas, than the more posterior regions. EEG and source estimation results may indicate that reduced availability of emotional information in the neutral face condition requires more sensorimotor engagement in deciphering emotion-related information than the full-blown happy or sad expressions that are more readily recognized.

The mirror neuron network (MNN) has been proposed as a neural substrate of action understanding. Electroencephalography (EEG) mu suppression has commonly been studied as an index of MNN activity during execution and observation of hand and finger movements. However, in order to establish its role in higher order processes, such as recognising and sharing emotions, more research using social emotional stimuli is needed. The current study aims to contribute to our understanding of the sensitivity of mu suppression to facial expressions. Modulation of the mu and occipital alpha (8 -13 Hz) rhythms was calculated in 22 participants while they observed dynamic video stimuli, including emotional (happy and sad) and neutral (mouth opening) facial expressions, and non-biological stimulus (kaleidoscope pattern). Across the four types of stimuli, only the neutral face was associated with a significantly stronger mu suppression than the non-biological stimulus. Occipital alpha suppression was significantly greater in the non-biological stimulus than all the face conditions. Source estimation (sLORETA) analysis comparing the neural sources of mu/alpha modulation between neutral face and non-biological stimulus showed more suppression in the central regions, including the supplementary motor and somatosensory areas, than the more posterior regions. EEG and source estimation results may indicate that reduced availability of emotional information in the neutral face condition requires more sensorimotor engagement in deciphering emotion-related information than the full-blown happy or sad expressions that are more readily recognised.Mu suppression to facial expressions 2

Mu suppression to ambiguous expressions 2 Increased sensorimotor activity during categorisation of ambiguous emotional expressions Abstract Actions are rarely devoid of emotional content. Thus, a more complete picture of the neural mechanisms underlying mental simulation of observed actions requires more research using emotion information. The present study used electroencephalography (EEG) to investigate mental simulation associated with facial emotion categorisation. Mu rhythm modulation was measured to infer the degree of sensorimotor simulation. Categorising static images of neutral faces as happy or sad was associated with stronger mu suppression than categorising clearly happy or sad faces. Results suggest the sensitivity of the sensorimotor activity to emotional information rather than visual attentional engagement, because further control analyses revealed (1) no effect of emotion type on occipital alpha modulation, and (2) no difference in mu modulation between the conditions of a control task, which required categorising images with the head oriented right, left, or forward as right or left. This finding provides evidence for the role of the sensorimotor activity in a higher form of mental simulation. Consistent with a predictive coding account of action perception, stronger mu suppression during attempted emotion categorisation of neutral faces may involve minimising the mismatch between predicted kinematics of a happy/sad face and the observed stationarity of neutral faces. KeywordsEEG; mu suppression; mirror neuron; sensorimotor activity; facial expression; predictive coding Mu suppression to ambiguous expressions 3