Neural, physiological and behavioral correlates of empathy for pain in Tourette syndrome

Persons with Tourette syndrome (TS) show altered social behaviors, such as echophenomena and increased personal distress in emotional situations. These symptoms may reflect an overactive mirror neuron system (MNS), causing both increased automatic imitation and a stronger tendency to share others’ emotions. To test this, we measured the individual level of echophenomena with a video protocol and experimentally induced empathy for pain in 25 participants with TS and 25 matched controls. In the empathy for pain paradigm, pictures of hands and feet in painful or neutral situations were presented, while we measured participants’ EEG and skin conductance response (SCR). Changes in somatosensory mu suppression during the observation of the pictures, as well as pain ratings and SCR were compared between groups and correlated with the occurrence of echophenomena, self-reported empathy and clinical measures. Our TS sample showed significantly more echophenomena than controls, but the groups showed no behavioral differences in empathic abilities. However, controls, but not patients with TS, showed the predicted increased mu suppression when watching painful compared to neutral actions. While echophenomena were present in all persons with TS, the hypothesis of an overactive MNS in TS could not be substantiated. On the contrary, the TS group showed a noticeable lack of mu attenuation in response to pain stimuli, questioning the normal functioning of the MNS in empathy for pain situations. In conclusion, the MNS remains an important area of study for TS, but overactivity of the system could not explain echophenomena and social symptoms of TS.