It is vital for social animals to interact with their fellow animals. In doing so, they not only have to consider who is giving which signals, but also who they are dealing with, what experiences they have had with their counterpart in the past and what the current mood is – a great cognitive challenge. Researchers have now used monkeys and bats to study how the brain processes such complex interactions in social groups. Accordingly, depending on which individual is currently acting and what the common history of the group members involved is, different neurons become active.
Similar to humans, social interactions play an important role for rhesus monkeys. They maintain friendly relationships beyond family ties and can remember who has done them good or bad in the past and adapt their behavior accordingly. Bats are also highly social animals. In the caves in which they sleep during the day, hundreds of individuals often romp close together, interacting with each other, for example when it comes to food, sleeping places or mating partners.
Group communication in focus
Two research teams have now independently examined representatives of these two animal groups – rhesus monkeys and Egyptian bats (Rousettus aegyptiacus) – to see how their brain processes complex group communication. A team led by Raymundo Báez-Mendoza from Harvard Medical School in Boston had groups of three rhesus monkeys each share fruit and not only observed their behavior, but also measured their brain activity in the prefrontal cortex. Maimon Rose and his colleagues at the University of California at Berkeley analyzed brain activity in the frontal cortex of Egyptian bats as they interacted freely in small groups.
“Most studies on communication, especially vocalizations, are usually done with solitary animals or pairs of animals, but so far hardly a study has been done in a real group,” says Rose. “However, many social mammals, including humans, usually interact in groups.” Until now, however, it was unclear how the animals’ brains are able to differentiate and classify individual conspecifics during group communication and to what extent the brain activity of the animals different involved individuals synchronized.
Specific neurons identify the speaker
The two current studies have now clarified these questions. “By following the inter-individual dynamics of groups of three rhesus monkeys, we discovered that certain neurons in the prefrontal cortex represent group behavior in detail,” reports Báez-Mendoza’s team. Depending on which of the conspecifics acted, different neurons were activated. “These not only reflected the identity of the other person, but also specific interactions, the social context, the actions and results,” report the researchers.
The neural representation was so detailed that the researchers were even able to use it to predict whether or not one monkey would be next to cooperate with another. If, on the other hand, the researchers briefly interrupted the neural activity in the monkey’s prefrontal cortex with the help of micro-stimulation, the animals were no longer able to make their decisions based on previous experiences with their conspecifics. While they usually gave a piece of fruit to fellow species who had earned a reputation as good “fruit givers”, this no longer played a role if the activity of the corresponding neurons was interrupted.
Worse synchronization with outsiders
Rose and his team also found that different individuals each have unique representations in the brains of their fellow species. Depending on which bat was just uttering sounds, different neurons were activated in the prefrontal cortex of their “listeners”. The researchers were able to tell from which animal the sound had come from just based on the neural activity in the brains of the other bats. They also found that group members’ brains synchronized during communication. If, on the other hand, the animals heard corresponding sounds outside of the communicative context, this was not the case.
Further experiments revealed that the degree of synchronization apparently also depends on how the respective “speaking” bat behaves in the group, i.e. whether it usually sits close to other bats or rather isolates itself. “We found that the bats that uttered their sounds within the group produced a much more accurate neural representation of their identity in the other bats and also triggered a much higher degree of brain synchronicity within the group,” says Rose. “While it is not entirely clear what exactly is going on, it appears that the behavior of the bats actually shifts their neural representation in the brains of the other bats.”
Neural Mechanisms for Social Intelligence
In an accompanying commentary on the two studies, which was also published in the journal “Science”, neuroscientist Julia Sliwa from the Sorbonne University in Paris writes: “The results are an important step in identifying the neural mechanisms that make it possible to interact in complex social structures – while taking into account the specific identity of the interaction partner and the shared history. “
Sources: Raymundo Báez-Mendoza (Harvard Medical School, Boston) et al., Science, doi: 10.1126 / science.abb4149, Maimon Rose (University of California, Berkeley) et al., Science, doi: 10.1126 / science.aba9584