## 1 Introduction
Specifically, simultaneous stimulation of cathodal tDCS in the contralesional M1 and 10 Hz rTMS in the ipsilesional M1 improved motor function and cortical excitability the most in patients with chronic stroke [16]. In addition, simultaneous stimulation mode was more effective in patients with subacute stroke compared to rTMS-only stimulation mode [3]. Ultimately, this dual-mode stimulation is believed to effectively regulate the interhemispherical imbalance of cortical excitability [17]. The effect of dual-mode stimulation is also observed through neuroimaging studies. In the fMRI study, simultaneous dual-mode stimulation had a greater effect on the interhemispheric connectivity of the contralesional M1. In particular, this increased interhemispheric connectivity between the contralesional M1 and the ipsilesional motor-related regions due to rTMS with the additional cathodal tDCS over the contralesional M1 [12]. This means that dual-mode stimulation would provide greater help in neurorehabilitation. In addition, as a result of the fMRI study, motor function was significantly increased by dual-mode stimulation in patients with subacute stroke [12; 18]. This is very meaningful in that the subacute stage of motor recovery leads to the highest biological recovery after stroke. However, clear evidence for changes in brain connectivity due to dual-mode stimulation using EEG signals is still lacking. Therefore, it is necessary to investigate the neuromodulation effect on EEG-based dual-mode NBS. Since the effect of NBS can vary depending on various factors, continuous research is being conducted on how to use NBS in effective neurorehabilitation [13]. Subtle differences in stimulation location can lead to significant changes in the functional improvement of the motor region [19]. In addition, in order to improve motor function, it is important to balance brain activity over the motor cortex on both sides. Another factor affecting the effectiveness of NBS is brain-derived neurotrophic factor (BDNF) polymorphism [20]. Due to these individual differences, some patients may experience significant motor function improvement as a result of NBS. Additionally, brain connectivity may vary depending on the location of the lesion. Hemispheric asymmetric indices differed depending on the location of the lesion in patients with chronic stroke, especially in beta bands, which are associated with motor function [21]. Significant differences in motor network dynamics during motor recovery between supra- and infra-tentorial ischemic strokes were observed [22]. In this respect, the location of lesions in stroke is also likely to be a major factor affecting the effectiveness of NBS. In this paper, the aim of this study was to investigate the neuromodulation effect after dual-mode NBS according to the location of the lesion using EEG signals. We hypothesized that the effect of regulating neuroexcitability and inducing neuroplasticity would vary depending on the location of the lesion. Furthermore, we compared the brain connectivity of each group according to lesion location before and after dual-mode NBS to the healthy controls. Here, the weighted phase lag index (wPLI), an indicator of functional connectivity between two channels, where \"channels\" refer to electrodes in EEG studies [23], and Granger causality (GC), an indicator of effective connectivity between two channels for causality [24], were used to explore interhemispheric and intrahemispheric connectivity. Next, cognitive-related networks from resting-state fMRI data have recently been shown to be associated with exercise recovery in patients [2]. In this respect, we also examined the relationship between the left dorsolateral prefrontal cortex (DLPFC) and M1s. These findings would contribute to the precise medical treatment for neurorehabilitation in the future by revealing the effect of NBS according to the location of the lesion.