Whether we're talking about a murder of crows or a crowd of people, social group dynamics can get incredibly complex. In each interaction, individuals within a group must juggle who is who, what is happening, whether they've met before and what happened in those past interactions. Keeping track of such details allows you to distinguish your best friend from your mortal enemy. In their new paper published in Science, Maimon Rose and colleagues from University of California Berkeley, USA, looked to unravel how complex ideas such as identity and context in social communication are encoded in the brain.
To address this question, the team studied a long-lived and highly social species, the Egyptian fruit bat (Rousettus aegyptiacus). These animals typically live up to 25 years in colonies with thousands of other bats. Throughout their lifetime, they form long-lasting social ties and only chat with neighbours in close proximity, making them ideal to study the neural mechanisms of group social communication.
To study the bat brains, Rose strapped tiny wireless hats onto groups of 4–5 bats. These hats simultaneously recorded brainwaves from each bat and allowed the scientists to identify which bats were conversing at any one time. From scanning 1153 single neurons from 7 different bats, the researchers found that certain neurons fired in response to the bat's own calls while other neurons fired when it listened to calls from other bats. Moreover, calls from specific individuals caused specific neurons (‘identity neurons’) to fire in response, suggesting that the bat brain encodes a single neuron for each buddy.
When scientists compared brainwaves from each member of a group of bats, they found that all group members were on the same wavelength, meaning their brain activity patterns were remarkably synchronized whether a bat was calling or listening to a call. This neural coordination during communication among friends remained stable over at least 2 weeks. Thus, these long-lived, highly social bats can form ‘best friendships’ that are stable over time and reliably encoded in their neural repertoire.
To study the bat behaviours, Rose and Boaz Styr then built an LED light-based bat-tracking system to trace which individuals like to spend more or less time close to the rest of the group. The authors found that the identity neurons of anti-social bats, which spend less time close to the rest of the group, fired less reliably in response to their respective bat buddies. Moreover, their brainwaves were less synchronized with that of others in the group.
To show that these patterns of neural activity are specific to social interactions, the researchers trained bats to call in a non-social context, this time in response to a reward rather than spontaneously. They found that in this context, much like in anti-social bats, identity neurons were less reliable indicators of identity and brain activity patterns of members in the group were less coordinated.
Many animals, including humans, are social creatures. Although communication often occurs in a group setting, prior studies had only looked at either one brain at a time or one side of communication at a time. This study provides novel insights into the neuronal process by which the complexities of group social communication are handled. Studies such as this one bring us one step closer to understanding what controls our ability to communicate gracefully in a group.