## 3 Results and Discussion
### MEG/EEG-Based Hyperscanning Research
#### 3.1.1 Cognition  
The cognition application makes up 47% (28/60) of the research done with the MEG/EEG neuro-imaging methodology. The majority of studies were done by giving participants a visual, auditory, or speech task. Computer games were used to investigate the cognition applications [72; 73; 74; 57]. Another task was facial expression or visual search activity [75; 76; 77; 19]. For example, [PERSON] [78] did the first study to associate joint attention with alpha and mu rhythm modulations and used an eye-gaze task. Some studies used listen/response activities [79; 80; 81; 27]. [PERSON] et al. [80] investigated interbrain synchronization patterns in pairs of participants interacting through speech by having participants alternate between the role of speaker/listener for semi-structured oral narratives without interpersonal visual contact. Some studies utilized in-person games or role-play [82; 83; 84; 34]. [PERSON] et al. [82] looked at how hyperscanning can be used in leadership/management of a business. This study had participants role-play as a leader and an employee during a work performance evaluation. This role-play showed information about leadership and communicative styles. Six studies looked at the neural-synchrony between musicians during a performance. Three of the studies looked at musicians who played guitar [85; 86; 25], and three other studies looked at musicians who played the saxophone [87; 23; 88]. One unique study was the first to look at the effect of physical touch (handholding) on pain alleviation [89]. Using couples that were either married or strangers, the study found that hand-holding during pain increases the neural synchrony between pairs and improves the accuracy of observer's empathic reaction based on how accurately the second participant rated his partner's pain level. SettingA majority of studies (25/28, 89%) were conducted in the lab while 11% (3/28) of the studies were done in a natural setting [87; 23; 89]. For example, [PERSON] et al. [87] demonstrated that the EEG methodology is suitable for high-quality EEG data in subjects playing in an ensemble outside of a lab. Recently, [PERSON] et al. [90] was the first study to investigate neural synchrony during meditation. Figure 3: Current state of the art of hyperscanning research. The two numerical values in the parenthesis indicate that, out of the 126 selected hyperscanning papers, the number of hyperscanning studies that used (a) each neuroimaging method (e.g., 21 fMRI/MRI papers) and its percentage (e.g., 21/126 = 17%), and that were conducted in (b) each application domain (e.g., 29 motor synchronization) and its percentage (e.g., 29/126 = 23%). In this experiment, a 60-year old French philosopher and meditation teacher led a meditation practice (without verbal communication) for himself and two male pupils in a natural meditation setting. _Orientation._ Of the 28 studies in the cognition application, 61% (17/28) were done with participants seated side-by-side, while 39% (11/28) were done with participants seated face-to-face. Studies on musicians were arranged side-by-side as they were recorded with EEG while playing their instrument [23; 25; 87; 91]. Recently, [PERSON] et al. [19] had pairs of male subjects look for the wrong pieces of a puzzle in order to quantify the neural synchrony between subjects during a collaborative process through EEG hyperscanning. _Group Size._ Eighteen percent (5/28) of the studies looked at the neural responses in more than two participants compared to pairs [23; 75; 87; 88; 91]. For example, [PERSON] et al. [88] was the first study on neural synchrony between musicians. This study evaluated the eventual occurrence of synchronous oscillatory brain activity across subjects through an EEG hyperconnectivity study done with a professional quartet. [PERSON] et al. [91] explored the role of interbrain synchronization based on brain network indices (e.g., small-worldness, efficiency) when playing in music in an ensemble. [PERSON] et al.