## 7 Discussion
### Limitations and Future Trends  
Besides all the presented scientific outcomes, which are clearly promising and effective in the context of the embodiment evaluation in MR environments, the presented review underlined that there is still a lack of a transversal and objective approach for the neurophysiological embodiment assessment. In fact, the performed literature review in the context of embodiment neural correlates highlighted that, even if the validated EEG-derived features appeared to be reliable in objectively evaluating embodiment in MR, the state-of-the-art methodologies are for the most part based on time-locked EEG features. Such an approach might limit the applications fields, since the time-locked EEG features evaluation, such as ERP, requires specific experimental design constraints, such as the accurate synchronization between the EEG traces and specific stimuli to add to the MR environment. This aspect might limit the validated embodiment methods evaluations in out-of-the-lab applications. Concerning the identified spectral correlates of embodiment in MR, the scientific literature proposed promising approaches. However, such approaches rely on EEG-derived spectral features also connected to Human Factors variation (e.g., mental workload), which might not be necessarily related to embodiment variations, but directly correlated with the human perception and reaction to the requested activities within MR environments. Similarly, the present work highlighted that several cardiac and electrodermal features were identified to be highly and significantly correlated with embodiment variations across different MR scenarios and applications, but still consistently dependent on the specific phenomena characterizing the activities included in the considered digital environment. In other words, the autonomic parameters identified in scientific literature are sensible to embodiment variations in MR within out-of-the-lab applications, but, at the same time, are still strictly correlated to the other cognitive variations induced by the specific experimental scenario (e.g., the SCL parameter was demonstrated to be significantly sensible to stress and arousal variations elicited by the performed experimental task [7; 79; 95; 96; 97], independently from the embodiment level). This aspect could lead to consistent misinterpretation in the context of the embodiment evaluation within different experimental environments. By considering all the above-mentioned findings, it appears to be clear that all the emerged neurophysiological variables cannot always and exclusively be associated with embodiment variations in MR, since they were demonstrated to be correlated with other HFs variations according to the experimental context. Therefore, the scientific gap consists of determining a standardized and transversal approach for the objective assessment of embodiment in digital environments. This could also be achieved by furtherly investigating the conceptual subcategorization of embodiment suggested by [PERSON] and colleagues [34] in their work, for which embodiment could be assessed through the evaluation of the different senses of agency, ownership, and self-location. In fact, the single evaluation of each component through a neurophysiological-based method would provide an objective measurement of the specific neural correlates associated with each component. More specifically, previous studies demonstrated that the SoA is associated with the EEG activity in premotor cortex, supplementary motor area, and parietal lobes [98; 99]; while the SoO is associated with the neural activity in primary somatosensory cortex [35; 36]; and the SoL is impacting on the activity in temporoporarietal junction and hippocampus [35; 37]. Therefore, in terms of future research, an interesting approach could consist of designing an experimental protocol including an exact dual experience between MR and real life, i.e., by requiring to the participants to perform the same experimental activities both in MR and in real life.