Technologies such as electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) are allowing scientists to scan multiple people’s brains as they interact in naturalistic settings—making deals, playing games, or simply talking to one another. Using these tools, researchers have found persuasive evidence for what is known as the “interactive brain hypothesis”: the premise that when people interact socially, their brains engage different neural and cognitive processes than when those same people are thinking or acting on their own.
