A considerable number of pain empathy studies investigated the activity of the skeletomotor system by means of transcranial magnetic stimulation (TMS). Motor corticospinal excitability (CSE) can be assessed by applying single magnetic pulses over the primary motor cortex and measuring the amplitude of the elicited motor evoked potentials (MEPs) recorded from the corresponding skeletal muscle. In a series of studies, Avenanti et al. have shown that observing needle penetration into a muscle, compared with observing touch at the same location, resulted in a decreased MEPs from the corresponding muscle of the observer (Avenanti et al.
2005,
2006,
2009a,
b; Minio-Paluello et al.
2006). This modulation of CSE was muscle specific, thus MEPs of the first dorsal interosseus muscle (FDI) of the observer’s right hand were reduced only in case they observed penetration of the FDI of the right hand. Furthermore, the effect depended on the bodily intervention (present for penetration, absent for pinprick), ethnic group membership (present for ingroup, absent for outgroup hands), and correlated with the intensity of pain attributed to the model, as well as with self-reported empathic traits (see also Fecteau et al.
2008). The authors also demonstrated that CSE of the corresponding muscle of the opposite hand is elevated rather than inhibited. A parallel has been drawn to an inhibitory effect of first-hand muscular pain on the excitability of motor cortex (Nijs et al.
2012). However, arguments have been raised that the modulations of CSE reflect the situational context so that the inhibition of CSE is the consequence of the fact that the painful stimulation cannot be avoided (De Coster et al.
2014). Furthermore, Bucchioni et al. (
2016) demonstrated that the inhibition of CSE occurs only when seeing the other’s hand in the first-person perspective, but not in the third-person perspective, and argued that the CSE inhibition may reflect an illusory bodily ownership (“embodiment”) of the other’s hand (also see Fossataro et al.
2018 and de Guzman et al.
2016). Using the same stimuli as Avenanti et al., our own group has documented that seeing needle penetrations, compared with seeing touch, elicits stronger suppression of sensorimotor mu and beta EEG oscillations, and that this effects gets stronger with increasing illusory ownership of the observed hand (Riečanský et al.
2015,
2019). These findings indicate that sensorimotor cortex is activated rather than inhibited by seeing needle penetrations into the hand from the first-person perspective and that the activation increases with increasing embodiment (Evans and Blanke
2013; Takemi et al.
2013). These results apparently contradict the findings from the TMS studies and the reasons for these differences across methodologies are currently not clear. In pain synaesthetes, for instance, observing hands in painful scenarios from the egocentric perspective elicits elevation, not reduction, of CSE (Fitzgibbon et al.
2012a) and a stronger suppression of central mu and beta EEG rhythms compared to control subjects (Fitzgibbon et al.
2012b; Grice-Jackson et al.
2017). Furthermore, Morrison et al. demonstrated that observing a needle pricking a fingertip facilitates withdrawal and inhibits approach movements (Morrison et al.
2007b). Several studies also indicate that observing pain in others elicits a non-specific movement facilitation (Morrison et al.
2007a; Han et al.
2017; Galang et al.
2017; Fabi and Leuthold
2017). In particular, a recent study by Galang and Obhi (
2019) has shown that observing needle penetrations into right hand from the egocentric perspective decreased latencies of button presses to go signals carried out with the right hand and this response facilitation was stronger after explicitly instructing observers to empathize with a person in pain.