## 4 Discussion  
The analysis of selected studies provides insights into the impact of EEG NFB on motor deficits in PD, addressing both of our research questions. First, as to whether EEG NFB can affect motor deficits in PD, the findings suggest that EEG NFB can indeed improve balance, coordination and mobility in individuals with PD. Although the long-term effects are still unclear, there is evidence that EEG NFB can improve quality of life, particularly in the early stages of the disease. This is consistent with the observed correlation between increasing SMR (13-15 Hz) and beta (12-15 Hz) rhythms and improvements in balance, mobility and stability, as indicated by motor performance tests. * **Improvement in balance:** Two of the selected studies aimed to improve balance issues using EEG NFB. This was tested using the Berg Balance Scale and the Biodex Test. In the randomized controlled trials by [PERSON] et al. [8] and [PERSON] et al. [37], statistically significant improvements in balance were observed. Descriptive results of improved balance were also reported by [PERSON] and [PERSON] in their case study. * **Improvement in mobility and stability:** The same studies also used scales to assess progress in mobility and stability. Both the TUG test and the Biodex test showed statistically significant improvements in the results measured after EEG NFB in PD patients. A case study also demonstrated improvements in mobility and stability through descriptive results. The selected studies varied in design, including case studies, pilot studies and randomized controlled trials, each offering distinct levels of reliability and generalizability The study by [PERSON] and [PERSON] [34] was a case study, while [PERSON] et al. [36] conducted a pilot study. The remaining three studies by [PERSON] et al. [35], [PERSON] et al. [8] and [PERSON] et al. [37] were randomized controlled trials. While case studies provide detailed individual outcomes, their results are descriptive and not easily replicable. In contrast, RCTs provide higher scientific reliability but still face challenges such as limited sample sizes. Variability was also evident in the rating scales used across studies and on increasing frequencies. Three of the five studies assessed the general motor abilities of PD patients using the UPDRS-III scale, but, contrary to expectations, the results did not indicate an improvement in motor abilities. This suggests that this scale may not detect minor progress in a short period, as it is designed to assess a broader range of motor symptoms, potentially reducing sensitivity. Studies that focused on increasing beta frequency showed promising results in improving coordination and balance, similar to those directed at SMR frequencies. Similarly, alterations in beta-gamma phase-amplitude coupling have been identified as potential biomarkers for motor symptom severity and monitoring therapeutic outcomes in PD patients (for the review please see [PERSON] et al. [38]). On the other hand, a decrease in theta frequencies in one of the two studies led to a deterioration in general well-being. Secondly, when asked which key factors are crucial for the successful implementation and wider application of EEG NFB, several important considerations can be found in the literature. Questions remain about the optimal protocols, such as the targeted frequencies, the duration of therapy, the form of feedback and the most effective NFB methods, which makes comparison between different studies difficult. It is emphasized that an individualized approach is needed, although clear guidelines for personalized protocols are still lacking. Although the long-term efficacy is still uncertain, there is a growing consensus that combining EEG NFB with other therapeutic approaches, such as physiotherapy or pharmacological treatments, may increase its potential.