Neuroscientists from the University of California, Berkeley used wireless neural recordings of Egyptian fruit flies to gain insight into the brains of social animals in complex group interactions. Credit: Michael Yartsev
Communicating with others in a group, whether it's at a dinner party with friends or at work, requires complex mental tasks. Our brains need to track who is speaking, what is being said, and our relationship with that person. After all, we tend to give the opinions of our closest friends more weight than those of complete strangers.
The journal Science published a study today that provides the first insight into the brains of social mammals in complex group interactions.
The study was conducted by neuroscientists from the University of California at Berkeley. They used wireless neural recording devices that recorded brain activity of Egyptian fruit bats.
Maimon Rose, a graduate student at UC Berkeley's NeuroBat Lab, said that most studies of communication, especially vocalization, are usually done with one animal or two animals. However, virtually none of these studies have been conducted with groups. However, most social mammals, including humans interact in groups. Especially Egyptian fruit bats like to be part of large colonies.
Researchers were able to track which bats voiced and simultaneously measure the neural activity in listening and vocalizing bats. This allowed them to determine how neurons in the frontal cortices of bats differentiated vocalizations made by themselves or others.
They also discovered that brain activity was highly correlated with vocalizations by bats when they compared neural recordings between the different bats. Surprisingly they discovered that bats who were more friendly to each other and spent more time together effected higher levels of brain correlations among the group members.
"Other neuroscience research has attempted to study small parts of these interactions individually. One study might study how neurons react when someone speaks. A separate study might then examine how neurons respond to that person's speech," Michael Yartsev (study senior author), an assistant professor of neuroscience and bioengineering at UC Berkeley. This study is the first to bring together all these pieces to create a complete picture of communication within a group.
There are thousands of roommates who squabble
Egyptian fruit bats, like humans, are social animals. These nocturnal bats spend their days in caves and crevices, while hundreds to thousands of others go about their daily lives. Studies show that bats often vocalize in order to fight for food, sleep space, and mating.
"These bats live a very long time. They can live for about 25 years. Their entire lives are spent in group social life," Yartsev stated. Their lives are built around the ability to communicate and live in groups.
Bats, even in laboratory settings, seem to prefer the company of others. They spend most of their time pressed against one another in tight groups. Apart from making clicking sounds for echolocation, Egyptian fruit bats don't engage in long-distance communication. They only vocalize to each other when they are grouped together.
Yartsev stated that you can see tens to thousands of animals if you go to these bat caves. It would be absurd for a bat shouting across the cave to another bat.
Because bats are able to only communicate with each other in tight social clumps, they make excellent subjects for studying group communication. If a bat calls out while within a cluster, it is likely that this is a sign that social communication has taken place. Boaz Styr (postdoctoral researcher at the NeuroBat Lab), said that this behavior presented technical difficulties for the research team.
Styr stated that it was difficult to determine which bat produced a vocalization because bats spend most of their time in close groups and can sometimes obscure one another. "Even though there were many microphones and high resolution cameras, it was difficult to identify which bat made a call at which point."
Four to eight bats were allowed free interaction in a darkened lab enclosure. They were also allowed to vocalize spontaneously. The team created wireless vibration sensors that bats could wear around the necks. These vibration sensors could be used to identify the bats who made each call.
Styr stated that the vibration sensors, in conjunction with our ability wirelessly to record neural data from multiple bats simultaneously, enabled us to create an experiment in which bats spontaneously communicated and behaved freely. It was difficult to get all these technical elements to work together, but it allowed us ask these important questions."
Researchers used an infra red camera to monitor the position of bats while they were socializing within a darkened enclosure. The researchers found that most bats prefer to be in close proximity to other bats. However, there were a few less friendly bats who would sometimes break from the group. Their calls didn't cause brain waves to "sync up", as they did not trigger the brain waves of other bats. Credit: The NeuroBat Lab
Neurons are for self and others
One set of experiments involved allowing groups of four to five bats to interact in a darkened lab enclosure. The researchers also carefully monitored each bat's brain activity and vocalizations.
The researchers found that in each bat's frontal cortex, an area believed to mediate social behavior in animals and humans, distinct sets of neurons were activated depending on the bat vocalizing. In other words, one vocalization would stimulate activity within one set of neurons while another would stimulate activity in a different set. The researchers were able to identify the bat that had spoken by simply looking at the neural activity of other bats.
"What these neurons were concerned about was "Am I making the phone call?" Or is someone else calling? Styr stated that vocalizations of any kind were not important. "Other neurons only detected when one bat in the group was speaking."
The NeuroBat Lab's earlier research has shown that bat pairs' brains tend to work together when they socialize. The study revealed that vocal communication is a common way for the entire group to sync up. The effect did not occur when bats heard the same sounds played back, suggesting that the phenomenon was only active communication between the members of the group.
Surprisingly, the level of brain correlation between the group members depended on which bat was speaking, with certain bats having greater synchronization with particular individuals. These inter-brain patterns, which lasted for several weeks, are presumably indicative of stable social relationships between the individuals.
Researchers conducted separate experiments that allowed eight bats to interact freely in a larger enclosure in order to better understand the effects of social dynamics on brain activity. They monitored the vocalizations of each bat and their neural activity. Additionally, they tracked the bat's spatial position relative the other bats in the group.
Rose stated that bats can identify and maintain stable social relationships with each other, even over extended periods of time and under different circumstances. We had this group of bats so we decided to map their locations to find out if it would reveal anything about their social relationships. Who likes whom and who is more sociable?
The team found that while the majority of bats in a "in-cluster", spent their time together, some bats who were not part of the group spent more time on the side. Surprisingly, they also discovered that vocalizations of bats affected the neural activity of other bats regardless of whether they were in-cluster or not.
Rose stated that "we found that the in-cluster bats voiced more accurately than the others and also generated a higher level of brain synergy within the group." Rose said that while it is not clear exactly what is happening, it appears that the behavior of out-of-cluster Bats shifts their neural representations in the brains.
Yartsev stated that understanding the neural underpinnings behind why certain individuals are able to navigate any social situation without difficulty could have significant implications for human mental health. The study will inspire neuroscientists and other social mammal researchers to look more deeply at group communication.
Yartsev stated that neuroscience often prefers to simplify and concentrate on one part of a complex process at a given time. The reality is that the social world can be complex. There is a lot of history and baggage when we spend time with friends. These include what happened yesterday, who the person is friends with, and how each person feels at that moment. Seeing the whole picture can be difficult, so it's worth breaking down the relationships and looking at each one individually.
Yartsev said that brains and animals have evolved to cope with complexity. I believe it is essential to understand the brain. We must embrace its complexity rather than fear it. And every time that we did this, we discovered something new and amazing. This, along with our other studies, will show that it is important to study the brain in all its complexity.
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Maimon Rose and colleagues, Cortical representation of group social communication in bats, Science (2021). Information from Science Maimon Rose and al., Cortical representation of group social communication in bats. (2021). DOI: 10.1126/science.aba9584
