Humans and many other animals express a range of social behaviors, from cooperation to aggression. But as innate as these behaviors may be, little is known about which brain regions control them.
But now, new tools can probe the brains of living animals while they are engaged in social interactions, providing insights into how the brain controls certain behaviors.
These tools — which involve electrodes implanted into the brains of animals — have also revealed that brains likely don't operate in isolation.
Four independent studies, presented Nov. 13 at the annual meeting of the Society for Neuroscience, highlighted some particularly interesting findings about the "social brain."
Among some surprises were findings that social aggression is closely associated with the brain's memory region, that cooperation is more a self-serving strategy than an empathetic one, and that there is biological evidence that two minds really can be on the same wavelength.
"We're beginning to see a striking aspect of the brain … that brains are wired for social interactions," said Dr. Robert Green, a professor of neuroscience and psychiatry at the University of Texas Southwestern Medical Center, during a news conference about the studies.
Although scientists have seen hints there must be an underlying brain architecture guiding social behavior, only now are they observing this architecture directly in living brains, Green told Live Science. This understanding could lead to treatments for antisocial behaviors, he said.
Green also noted these new insights are a result of studying brains interacting with each other simultaneously, as opposed to traditional studies of probing only one brain at a time in isolation.
One research group, from Columbia University in New York, investigated the phenomenon of social aggression, which is aggression toward a fellow species member as opposed to prey. The researchers found that the hippocampus, which is the brain's memory center, appears to drive this type of aggression in mice — in this case, the attack of one mouse by another who didn't recognize it as a friend.
"The second that aggression started is when [nerve signals from the hippocampus] turned on really strongly," said Félix Leroy, a neuroscience associate research scientist at Columbia University who led the study. "We're now trying to look at the exact relay of signals in these brain regions to confirm that this burst of activity precedes aggression."
Leroy's team also found that they could block aggression by stimulating a region of the hippocampus called CA2. The findings imply that CA2 could be a therapeutic drug target to treat abnormal aggression associated with neuropsychiatric diseases, Leroy said, though much more research is needed to confirm such effects in humans.
In another study, scientists at the University of Pennsylvania found that strategic thinking, not empathy, may underlie cooperative behavior so common in primates. These researchers constructed an experiment in which rhesus macaques were taught play a computerized version of the classic game of "chicken," which itself sounds like an amazing feat. But there's more.
When playing against each other, two monkeys could strategize on ways to avoid crashing into one another and reap the highest rewards together. When just one monkey played against a machine, though, and the other one simply watched, the game-playing monkey suddenly had no interest in maximizing rewards for his one-time game companion. Instead, the game-playing monkey employed a different strategy to get the highest rewards only for himself.
"We found that neurons in a part of the brain [previously] linked to strategic thinking, but not in a part of the brain linked to empathy and shared experience, respond selectively when rhesus macaques cooperate," said Wei Song Ong, a postdoctoral neuroscience researcher at the University of Pennsylvania, who led the study.
Ong said she wasn't ready to concede that empathy isn't an important human trait, but she added that social cooperation may be much more of a selfish act than people would like to think.
What could be more social than brains acting in sync? Similar brain activity may be fundamental for how animals, including humans, interact to form social bonds, according to Dr. Miguel Nicolelis, a professor of neuroscience at Duke University School of Medicine in North Carolina.
Nicolelis' group built an experiment in which one monkey drives a vehicle to get a fruit reward while another monkey watches. Each time the driver monkey gets a fruit reward, the spectator monkey gets one, too. So they are linked, Nicolelis said during the news conference.
"To our shock, what we found is that as these animals are interacting … both brains are highly synchronized," Nicolelis said. "We have, in fact, in some instances, 60 percent of [the firing of neurons] in the motor cortexes of both monkeys [happening] precisely the same time."
The synchronicity became more precise as the monkey got closer to the fruit reward or, as shown during a second experiment in the study, as the spectator monkey helped control the vehicle remotely, Nicolelis said. The finding suggests that the optimal performance of social tasks, such as gathering food, requires synchronization of brain activity across the brains of all subjects involved — in other words, with everyone being on the same wavelength.
Conversely, Nicolelis said that some antisocial neurological disorders, such as autism, may result in an inability to establish such interbrain synchronization. He said he hopes to test this in his lab with human subjects.
The "social brain"
Taken together, the collection of studies presented at the news conference "opens a new chapter in neuroscience, [as we] have the ability to assess multiple brains simultaneously," Nicolelis said.
"We can no longer think of brains in isolation," Nicolelis said. "The 'social brain' idea that we are talking about supersedes the notions that [scientists] have developed for brains in isolation, because the brain is not just a passive device alone in the world. … The action on one animal involves the actions of other animals."
Whereas neuroscience has, up until recently, focused on the study of neurons or networks of neurons, the new reality is that behavior arises from a network of different brains interacting, Nicolelis said.