## 4 Discussion
Functional connectivity refers to the pattern of statistical dependency between various units within the nervous system. The pattern of connectivity is a statistical relationship measured as cross-correlations or coherence. Brain connectivity is, therefore, crucial to understanding how neurons and neural networks process information. Thus, the enhanced functional connectivity in the M1 region resulting from acupuncture, as observed in our study, could also be interpreted as the effects of enhanced motor recovery (Figure 5e). In PD patients, several studies have reported cortical motor reorganization. Frontal cortical activity tends to increase in PD patients during walking and balancetasks [44], in addition to higher prefrontal activation in PD patients compared to healthy controls during walking and obstacle negotiation, as observed using fNIRS [45]. In our study, increased functional connectivity was observed in the PFC region at follow-up 4-weeks after acupuncture treatment (Figure 5f). These results can also be described in terms of the effects of the recovery of motor and cognitive functions. On the other hand, the CG did not show significant changes in HbO and connectivity in these areas (Figures 4 and 5). These different observations may depend on the effects of acupuncture treatment. Hence, the findings of our current study show that acupuncture could increase the neural plasticity related to motor function by enhancing the M1 and PFC regions in PD patients. There are some limitations to this study. First, this study was conducted in the assessor-blinded, randomized, controlled, parallel-group trial, and clinical outcomes such as gait parameters and UPDRS (Unified Parkinson's Disease Rating Scale) were also measured. However, [PERSON] et al. studied the primary outcomes and the neurotransmitter levels for acupuncture effects, and the findings were published [15]. In this study, fNIRS data, which are assumed to be related to therapeutic effects, were used. We only considered the brain function to investigate the effectiveness of acupuncture for PD patients. In addition to our proposed evaluation of brain function, it is necessary to analyze with primary outcomes. However, we conducted different tasks to assess gait performance and hemodynamic responses. It is necessary to perform the same task to compare gait performance and hemodynamic responses for future work. A second shortcoming is the use of a treadmill instead of over-ground walking. However, a treadmill was necessary for this study since a stationary fNIRS device was used to measure brain activation. A treadmill velocity of 0.1 km/h was not adjusted due to the risk of falling in participants, and the number of walking trails could not be increased because [PERSON]'s patients were unable to walk for a long time. Thirdly, it is difficult to judge the effect of each acupoint when several acupoints are used in a session. Further study is needed to clarify the effects of specific acupoints. Finally, the duration of the intervention was short, and the sample size was small. Nonetheless, we have to point out that the findings presented here are just a preliminary study of the effects of acupuncture on the brain network of PD patients. Further studies with a larger sample size and longer duration of intervention are needed to confirm these results.