Friend or enemy? Unique neurons in the brain control social interaction, study finds


Neurons live in a society, and scientists have just found the ones that can enable us to thrive in our own society.

Like humans, individual neurons are surprisingly unique. In addition, like humans, they are in constant contact with each other. They connect to “friend groups” of neural circuits, split up when things change, and reconnect in new cliques. This flexibility allows their collective society (the brain) and their owners (us) to learn and adapt to an ever-changing world.

To reconstruct neural circuits, neurons continuously monitor the state of their neighbors through nerve branches that grow from a round body. These are not just passive phone lines. Along each branch are small, dual-purpose units called synapses, which allow neurons to chat with a neural partner and record previous conversations. Each synapse keeps a “log” of communications passed in its physical and molecular structure. By “viewing” this log, a neuron can passively determine whether or not it should network with that particular neuron partner – or even a set of partners – or avoid any interaction in the near future.

Apparently neurons can do the same for us. This week, listening to the electrical chatter of neurons isolated from rhesus macaque monkeys, Harvard scientists, led by Dr. Ziv Williams, focused on a particular subset of neurons that help us distinguish friends from enemies.

Neurons, sprinkled over the frontal parts of the brain, are surprisingly powerful. As their ape hosts hung out for a game night, the small computers tracked each player’s behavior: were they more cooperative or selfish? Over time, these “social agent identity cells” stealthily map the entire group dynamic. Using this information, the monkeys can then decide whether to team up with other monkeys or avoid them.

It’s not just a correlation. By modeling the electrical activity of these neurons, scientists were able to accurately determine any monkey’s past decisions and, breathtakingly, predict their future decisions, essentially “reading minds” of the next move of the monkey. animal. When the team altered neural activity with a short burst of electrical zaps, the monkeys lost their social judgment. Like the new kid on the block at school, they couldn’t decide who to befriend anymore.

“In the frontal cortex, these neurons appear to be tuned for possible action by their peers, representing them as communication partners, competitors and collaborators,” wrote Dr Julia Sliwa of Sorbonne University in Paris, who did not participated in the study.

Although the findings come from monkeys, they are among the first to link the activity of individual neurons to an extremely complicated but necessary aspect of our lives. These data “are major steps in identifying the neural mechanisms that allow maneuvering in a complex social structure,” she said.

My brain’s take on you

We often think of neurons and circuits as hardware components that represent we: our perception, our memory, our decisions, our feelings. Yet large parts of the brain are dedicated to representing other people in our outside world.

A famous example is the “Jennifer Aniston Neuron”. In 2005, an experiment showed that a single neuron in a person’s brain could react to a particular face, such as Aniston’s. A landmark moment for neuroscience and computer vision, the study raised a cheeky idea: that a single neuron has the computing power to encode a person’s physical identity.

In the real world, it gets more complicated than just identifying a face. A person’s face comes with the story – is this the first time I’ve met them? What is their reputation? How do I feel about this person?

Much of the work on how our brains handle social interactions comes from studying groups in music studios or teacher-student dynamics in classrooms. Here, brain activity is captured with wearable devices, which measure brain waves that sweep through parts of the brain. These studies show that when we make music or watch a movie together, our brain waves synchronize. To put it another way, our brains connect to other people’s brains, but when, how and why this happens is a mystery.

The monkey sees, the monkey does … or not

The new study takes an unprecedented look at the brain as it interacts with another being.

It starts with a simple game of economics. Three monkeys are seated around a rotating table. Each has a brain implant in their dorsomedial prefrontal cortex (dmPFC), which was previously linked to social behavior, to capture the electrical buzz of individual neurons. Three trays of food are spread out on the table, some with juicy apple slices, others without. In turn, one monkey (the “actor”) can turn the table to decide whether or not to give a slice of an apple to another monkey (the “receiver”) or to keep it for himself. This setup allowed the team to monitor the neuronal activity of each monkey as they interacted with others in the trials.

The task may seem simple, Sliwa said, but it taps into “the foundation of human economic commerce: give, receive and reciprocate.”

In just a few sessions, the monkeys displayed a clear tit-for-tat behavior. When a monkey received a previous gift of an apple, he was more likely to return the favor. When trapped, he would retaliate more often when given the chance. These transitional duopolies, the team said, depended on the actor’s past behavior – his “reputation”, so to speak – throughout 20 tries, rather than an immediate past. If a monkey exhibited selfish behavior, the others would retaliate by not offering it food. These decisions were based on real interactions: replacing a monkey with a stuffed animal of a similar appearance erased the behavior.

As the monkeys played, a group of dmPFC neurons buzzed with activity. By recording more than 500 unique neurons, the team found 50 that triggered when they received a reward from a particular monkey. In other words, these neurons have captured a historical record of interactions with specific individuals.

Using machine learning, the team then decoded the signals from each neuron to see if their activity predicted the responses of the monkeys, as actors or recipients. The algorithm could analyze the actor’s action before it happens with nearly 90% accuracy. As the trials progressed, the accuracy of the recipient’s identity gradually increased to around 70%.

“The activities of these neurons contained detailed representations about specific interactions within the group,” said the authors.

Through brain stimulation, the team could also temporarily rewrite naivety in the brain. In one test, the team disrupted the signals of these social neurons with short bursts of electricity before a monkey made the decision to reciprocate or fight back. The result? The monkey had less ability to decide whether to be friend or foe.

Multi-level brains

This study is not the only one to seek to broaden our field of understanding of social cognition. A separate study in bats in the same Science problem has also shown that our brains change rapidly and adapt to multiple social interactions; you can quickly become friends with someone, while other, potentially stronger bonds take longer to form.

We now understand why this is the case. Our world is made up, in essence, of a multitude of brains: each neuron is a minicomputer in a larger group that collectively forms the mind of a human; each human, in turn, interacts in a collective consciousness to chart the future of our species and our planet.

Traditionally, scientists have often focused on a single interaction, a single brain, or a pair of individuals. This is not the world we normally live in.

“These studies… highlight that in the future, it will be necessary to navigate between two levels of investigation to fully grasp social intelligence: that of the group of brains and that of the individual brain,” Sliwa said.

Image Credit: Gerd Altmann from Pixabay

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