## 3 The Mechanisms Behind Broken MNs in ASD and Schizophrenia
### Mu Rhythm Suppression in ASD
On the other hand, the clinical group demonstrated a larger value of RP for the congruent condition in comparison to the baseline, similarly to the incongruent condition, which implies elevated brain activation for motor preparation in both congruent and incongruent observations, while the baseline condition remained neutral. Comparing the compatible and non-compatible trials, no particular difference was reported. Crucially, the outcomes of the study show that the neural mechanisms underlying the motor interference effect in high-functioning ASD manifest discrepancies in the early stages of motor preparation rather than in higher-level cognitive processes, e.g., interpreting social cues, which contradicts the theory of \"broken\" MNs in ASD. Another study that measures \(mu\) rhythm suppression in ASD through the observation of gestures is that of [PERSON] et al. [60]. The objective of their study was to test the integrity of the MN hypothesis in ASD by administering an EEG experiment that measured \(mu\)rhyth suppression over the sensorimotor cortex while the participants observed and later imitated gestural hand movements. The study involved two groups of participants, 20 male adolescents and young adults, and 20 age-matched neurotypical controls. The two groups were required to complete an eye-tracking and an EEG test that included four conditions: _baseline_ condition (observation of a static object on a screen), _hand_ condition (observation of a video-recorded gesturing action), _dot_ condition (observation of a video with a white dot), and _execution_ condition (manipulation of an object in the same manner as in the _hand_ condition). The study also controlled for fixation duration and normalised fixation number on the stimuli to account for potential differences in visual attention. The results strongly support the inefficacy of the theory of dysfunction in the MNS in ASD. Specifically, _mu_ suppression over the sensorimotor cortex in the observation and imitation conditions did not present differences between the two groups. Essentially, _mu_ rhythm suppression was stronger in both groups during the observation of the hand rather than the moving dot. Contrasting previous research [61], no correlation between _mu_ rhythm suppression and imitation was detected. Although the ASD participants scored lower than neurotypicals in the imitation condition, the _mu_ rhythm suppression was not different from controls. The outcomes highlighted the heterogeneity of ASD in terms of traits, and concluded that the MNS activation appears to be intact to a certain extent. A more recent study by [PERSON] et al. [62] examined the way _mu_ suppression is modulated in ASD by visual attention during the process of perceiving biological motion. The researchers recruited 20 participants diagnosed with high-functioning ASD, and 20 age- and sex-matched healthy controls. An EEG paradigm was conducted to measure the suppression of _mu_ rhythm over the sensorimotor cortex while participants were required to watch point-light displays presenting biological motions, e.g., walking, cartwheeling, free-throwing and underarm throwing, as well as non-biological motion, e.g., moving dots. Eye-tracking technology was used to monitor visual attention and ensure that participants were fixating on the stimuli. The EEG findings showed that visual attention in both groups had a significant impact on _mu_ suppression; nevertheless, _mu_ rhythm suppression in the ASD group was reduced compared to that of the control group during biological motion observation. This finding can be interpreted as a cue for neural deviations in biological motion processing in ASD, and that visual attention is not the only determining factor for impaired _mu_ rhythm suppression. Furthermore, a positive correlation was detected between level of _mu_ suppression and social abilities in the group with ASD, thus revealing an association between social cognition and _mu_ suppression. The study by [PERSON] et al.