In the Iterated Prisoner's Dilemma, a player can act as a Cooperator (C), as a Defector (D), or can adopt a Tit-for-Tat (T) strategy. Therefore, the outcome of each round, or trial, of the game can be one of the six possible combinations of the individual actions. Three of them (CC, DD, and TT) are called here “pure” strategies because the two players adopt the same action, while the others (CD, CT, and DT or equivalently DC, TC, and TD) are called “mixed” strategies. For each of the 26 pairs of players, we obtained a hyper-brain network (see details in Materials and Methods), for each of the six possible outcomes, and for each frequency band Theta (4–7 Hz), Alpha (8–13 Hz), Beta (14–29 Hz) and Gamma (30–40 Hz).
