When research on so-called interbrain synchronicity emerged in the 2000s, some scholars dismissed it as parapsychology, a trippy field of the 1960s and 1970s that claimed to find evidence of ghosts, the afterlife, and other miracles of the paranormal.

In 1965, for example, two ophthalmologists published an absurd study of 15 pairs of identical twins in the renowned journal Science. Each twin with electrodes on their scalp was placed in a separate room and asked to blink on command. In two of the couples, the study reported, one twin showed different patterns of brain activity while the sibling in the other room blinked. Doctors called it “extrasensory induction”.

“The paper is hilarious,” said Guillaume Dumas, a University of Montreal social physiologist who has studied brain-to-brain synchronization for more than a decade. In that distant era, he said, “There have been many articles with methodologically questionable conclusions that claimed to demonstrate synchronization between the brains with two people.”

However, since then, many in-depth studies have found brain synchronicity to occur in human interactions, starting with a 2002 article describing how data from two brain scanners is collected and merged simultaneously when two people are playing a competitive game. This enabled the researchers to observe how both brains were activated in response to each other. In a 2005 science paper, this “hyperscanning” technique showed correlations between activity in the brains of two people when they were playing a trusting game.

In 2010, Dr. Dumas found using scalp electrodes that two brains exhibited coupled wave patterns when two people spontaneously imitate the other’s hand movements. It is important that there was no external metronome – like music or a turn-taking game – that encouraged the couples to adjust to each other. it happened, of course, in the course of their social interaction.

“There’s no telepathy or scary thing in the game,” said Dr. Dumas. Interacting with someone else is complicated and requires a continuous feedback loop of attention, prediction, and reaction. It makes sense that the brain can map both sides of this interaction – your behavior and that of the other person – at the same time, although scientists still know very little about how this happens.