## 3 The Mechanisms Behind Broken MNs in ASD and Schizophrenia
### Mu Rhythm Suppression in Schizophrenia  
Mirror neurons have received quite some criticism in research in recent years due to controversial findings of studies and the soundness of the hypotheses concerning the exact function and significance of the MNS [65; 66]. Nevertheless, they have also drawn significant attention, as they have been shown to be actively involved in complex cognitive processes, such as empathy, mentalising, perspective taking, language and imitation [67]. As mentioned before, the MNS has mostly been researched in ASD, mainly due to the hypothesis of the \"broken mirror neurons\" which negatively affect language, Theory of Mind and social navigation [68]. Nevertheless, as shown in the previous section, the results do not demonstrate a clear consensus as to the role of the MNS in social and cognitive discrepancies in autism [69]. Research on the connection between the functionality of the MNS and schizophrenic symptoms has gained ground over the last decade. Schizophrenia is often characterised as the disorder of the \"social brain\" [70], which underlines the attenuations in social cognition that schizophrenic patients exhibit. Similarly to ASD, the MNS system has also been investigated in schizophrenia using a variety of neuroimaging methods, each of which measures different aspects of the functions of the MNS (ex. fMRI measuring fluctuations in blood oxygenation, MEG measuring alpha band suppression and gamma band amplification, TMS, EEG measuring \(mu\) rhythm suppression, and electromyography to measure rapid face muscle activation during observation of facial expressions). With respect to \(mu\) rhythm suppression as a proxy for MNS activation, research demonstrates abnormalities in the MNS in schizophrenia, which are mainly reflected in varying levels of \(mu\) suppression. Variation in \(mu\) rhythm suppression has in turn been linked to deficits in Theory of Mind, empathy, emotion recognition and processing of social cues [71]. Several studies have explored \(mu\) rhythm suppression in patients with schizophrenia; however, the outcomes are heterogeneous. [PERSON] et al. [72] conducted an EEG study to explore impairments in the functioning of the MNS in patients with schizophrenia as indexed by \(mu\) suppression. The participants of their study included 32 outpatients diagnosed with schizophrenia, and 26 controls with no clinical diagnosis The two groups took part in an EEG paradigm, which involved six conditions of an either observed or executed action. These conditions contained varying levels of social interaction. In addition, validated empathy questionnaires were collected from the participants. The results revealed that both groups exhibited a crucial linear increase in \(mu\) rhythm suppression with respect to those conditions that contained a higher demand for socialisation; however, neither interactions nor group differences were found to be significant. In the questionnaires, patients described their empathy and mentalising ability as being low, nevertheless, as evinced from the \(mu\) suppression measurements, their MNS functioning appeared to be relatively intact. The researchers concluded that there was an impairment in emotion recognition processing in schizophrenia, with no evidence in favour of inability of experiencing them. However, it should be mentioned that the tasks in [PERSON] et al. 's [72] study involved non-complex social and emotional conditions, which may have biased the interpretation of the results. Other studies, on the other hand, have reported reduced \(mu\) rhythm suppression in patients with schizophrenia. [PERSON] et al. [73] investigated the efficacy of the MNS operation in individuals with schizophrenia. The researchers' objective was to detect whether the occurrence of psychotic episodes of the illness was attributed to attenuations of the MNS system by measuring \(mu\) rhythm suppression.