“Scientists Drove Mice to Bond by Zapping Their Brains With Light: The Study, a Tour De Force in Bioengineering, Comes After Two Decades of Research on Brain-To-Brain Synchrony in People”, 2021-05-25 (; similar):
Late one evening last March, just before the coronavirus pandemic shut down the country, Mingzheng Wu, a graduate student at Northwestern University, plopped 2 male mice into a cage and watched as they explored their modest new digs: sniffing, digging, fighting a little.
With a few clicks on a nearby computer, Mr. Wu then switched on a blue light implanted in the front of each animal’s brain. That light activated a tiny piece of cortex, spurring neurons there to fire. Mr. Wu zapped the 2 mice at the same time and at the same rapid frequency—putting that portion of their brains quite literally in sync. Within a minute or 2, any animus between the 2 creatures seemed to disappear, and they clung to each other like long-lost friends. “After a few minutes, we saw that those animals actually stayed together, and one animal was grooming the other”, said Mr. Wu, who works in the neurobiology lab of Yevgenia Kozorovitskiy.
…The experiment, published this month in Nature Neuroscience, was made possible thanks to an impressive new wireless technology that allows scientists to observe—and manipulate—the brains of multiple animals as they interact with one another.
…Weizhe Hong didn’t know about any of these human studies when, a few years ago, his team stumbled upon the same sort of synchrony while recording from brain cells of interacting mice. “For about 6 months, we were very puzzled by it”, said Dr. Hong, a neuroscientist at the University of California Los Angeles. “I just found it too good to be true, too surprising to me.”
In most social interactions, after all, the 2 interacting animals aren’t doing the same thing at the same time; in a conversation, one person may listen while the other talks. So it did not immediately make sense to him why his mice would show such robust neural synchrony. But after digging into the scientific literature, he said, “I realized, oh actually, there’s 15 years of history of studying human synchrony.”
In their experiments, Dr. Hong’s team recorded this synchrony in a part of the brain called the medial prefrontal cortex, which had been linked to a range of social behaviors. Certain neurons in each animal’s brain seemed to encode the animal’s own behavior, whereas other cells’ activity correlated with the behavior of the other animal. There was some overlap between the 2 groups, suggesting that certain cells were responsive to both animals. These findings could be related to previous studies of “mirror neurons”, which fire when an animal acts or when it observes that action in another animal, although that link is far from clear, Dr. Hong said. “Whether they’re mirror neurons or not is definitely something we’re very interested in”, he added.
…The Northwestern researchers who carried out the new study in Nature Neuroscience were familiar with these human and animal experiments on interbrain synchrony. “It seemed interesting and a little bit strange”, Dr. Kozorovitskiy said. She thought the phenomenon could be further probed with a new tool they had developed to manipulate the brains—and activities—of animals.
Their tool involves optogenetics, a technique that uses a tiny LED light, implanted into an animal’s brain, to activate discrete groups of neurons. (A gene that encodes a light-sensitive protein derived from algae is first inserted into the neurons of interest, to make them responsive.)
But studying social behavior with optogenetics had historically been difficult because the light source was typically attached to the animal’s head through fiber-optic cables, which interfered with the animal’s normal behavior. So John Rogers, a biomedical engineer at Northwestern who specializes in bioelectronics, developed tiny wireless devices that, once implanted, can be controlled remotely by a nearby computer.
“Because everything is implanted, mice can behave naturally and they can socially interact with one another naturally”, Dr. Rogers said. “You don’t have the cables that get tangled up, and there’s no head-mounted gear” for the mice to gnaw on.
The tool also allowed researchers to independently control multiple devices—and multiple animals—at once. Dr. Rogers and Dr. Kozorovitskiy began looking for a way to test it. Dr. Kozorovitskiy had seen the Cell study showing that interacting mice produce synchronies in the medial prefrontal cortex. Perhaps, she thought, the optogenetic device could test the converse relationship: If 2 animals’ brains were synchronized, would the animals become more social?
The answer, as Mr. Wu discovered that late night last spring, was yes. The results may suggest that brain synchrony is a causal driver of social behavior—and is more than just a byproduct of brains performing similar activities, or thinking similar thoughts, in a shared environment.