Figure 1. Experimental setup and behavioral results.

(A) Session 1: Participants were asked to straighten their arms, point and hold their index fingers toward each other, and look at the other participant's fingertip. They were instructed to look at the other participant's finger while holding their own finger as stationary as possible. One participant was instructed to use left arm and the other was instructed to use right arm. Session 2: Same as the session 1, except participants changed the arm from left to right and from right to left respectively. Session 3: One participant (leader, who was randomly selected from the naïve participant pair) was instructed to randomly move his finger (in the approximate area of 20×20 cm square) and the other (follower) was instructed to follow. Session 4: Same as the session 3, except participants changed the arm from left to right and from right to left respectively. Session 5 and 6: Same as the session 3 and 4, Session 7 and 8: Same as the session 1 and 2. We call sessions 1–2 the pre-training sessions, the sessions 3–6 the training sessions, and the 7–8 the post-training sessions. (B) Hyperscanning-EEG setup. The EEG data was passed through a client to a EEG server and database, which was regulated by an experiment controller. Client computers received fingertip movement information from the two participants. Two EEG recording systems were synchronized using a pulse signal from the control server computer delivered to both EEG recording systems. (C) Average cross correlation coefficients of fingertip movements in each condition (pre-training, post-training, and crosscheck validation) with its standard errors (gray). The training significantly increased finger movement correlation between the two participants (p<0.03). No significant correlation was found in crosscheck condition (i.e. cross correlation results after random shuffling of participants, p = 0.62). Results are shown as means ± s.e.m. Statistical analyses performed using a two-tailed student's t-test.