## 3 The Mechanisms Behind Broken MNs in ASD and Schizophrenia
### Mu Rhythm Suppression in ASD
[63] aimed to investigate MN activation in individuals with ASD in the process of making inferences about other people's intentions. In total, 43 participants took part in the study, distributed in two groups in compliance with the level of autistic traits. The 20 neurotypical controls that participated in the study reported no history of mental or neurological illness. The study used both transcranial magnetic stimulation (TMS) and EEG experiments to measure MNS activity, giving emphasis on the connection between autistic traits and neural responses during mentalizing tasks. The participants were instructed to watch short clip videos with mentalizing and non-mentalising actions, and place a judgement afterward with respect to the intention of the action performed. The study employed three screening tasks: an EEG task that was conducted during the projection of the videos, an eye-tracking task and a TMS-induced EMG (electromyography) task. In terms of _mu_ rhythm suppression, this was found to be at a lower level in the right hemisphere among participants with higher level of autistic traits when performing in the mentalizing task. Nevertheless, _mu_ rhythm suppression on the right hemisphere did not present significant correlation with how well the participants performed in the task. Notably, there was a positive correlation between lower MN activation in the left hemisphere and poor performance in the mentalising task, with no present effect occurring from the autistic traits. TMS-induced MEP did not present any significant variation between ASD individuals and controls. Similarly, no visual processing differences were reported for the eye-tracking task. The authors concluded that attenuated MNs and impaired ToM in ASD are the reasons behind the irregularities of MN activation in the right hemisphere. [PERSON] et al. [64] revisited the MN hypothesis aiming by placing emphasis on two main aspects of the existing EEG literature: the functional segregation of \(mu\) rhythm into two discrete sub-bands (8-10 Hz and 10-12/13 Hz), and the focus on central electrodes (C3/C4) in previous studies in ASD. Ten high-functioning individuals with ASD and 30 age-matched healthy controls participated in the study. The two groups were tested on a task involving three conditions, namely simple observation of gestures, free imitation of gestures, and imitation of a pre-recorded video. The outcomes of the study revealed a distinct pattern of \(mu\) suppression in the ASD group compared to the TD controls. Specifically, when the \(mu\) rhythm was analysed as a homogeneous phenomenon covering the 8-13 Hz frequency range, no significant differences were found between the groups. However, when the two sub-bands were distinguished, a different \(mu\) response to observation appeared for subjects with ASD in the upper sub-band (10-12/13 Hz) over the sensorimotor cortex, while the lower sub-band (8-10 Hz) responded similarly in both groups. Source reconstructions demonstrated that this effect was related to a joint \(mu\)-suppression deficit over the occipito-parietal regions and an increase over the frontal regions in the ASD group. The researchers argues that \(mu\) suppression deficits in individuals with ASD do not support a global irregular functionality of the MNS but are rather specific to the neural mechanisms underlying the observation of intentions.