2024-03-23 08:00:50
Thanks to an intracranial implant placed in the brains of macaques, American and Canadian neuroscientists managed to observe the brain signatures associated with 24 social behaviors at the level of individual neurons.
Quebecer Sébastien Tremblay is one of the first authors of the study published in the journal Nature (New window) (in English) which details this breakthrough, achieved using technology whose precision far exceeds that of magnetic resonance imaging.
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Sébastien Tremblay and Camille Testard, co-first author of the study.
Photo: University of Pennsylvania
Understanding the neurobiology of primate behavior also means understanding that of humans, recalls Dr. Tremblay, assistant professor at the Faculty of Medicine at Laval University and researcher at the CERVO center.
From one primate to another
And to achieve this, the macaque is the perfect animal model, since it shares approximately 95% of its genetic code with humans.
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Macaques during a grooming session.
Photo : Lauren Brent
It is a monkey that shares many elements of our anatomy, our immune system, our social and intellectual behaviors, recalls Dr. Tremblay.
However, even today, our understanding of the neurobiology of monkey behavior derives largely from artificial tasks performed in highly controlled laboratory environments. How then can we succeed in seeing what is happening in the monkey’s brain in a natural environment, without restricting its movements?
An implant to the rescue
Every great discovery is born from technological innovation, notes Sébastien Tremblay. However, we needed to solve the technological problem to allow us to record brain activity in a free-ranging monkey, which can move and interact as it wants.
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The Utah Array, the brain implant used in the study.
Photo : Blackrock Neurotech
He and his colleagues took up the challenge by developing a neural interface implant comparable to that of billionaire Elon Musk’s Neuralink. An implant placed inside the brain which, through a wi-fi network, propagates neural data wirelessly which is collected in a computer without constraining the participant’s movements.
These intracranial implants give us access to the activity of hundreds of neurons inside the brain, which we are able to listen to with millisecond precision. This data is recorded wirelessly, while the monkeys behave naturally.
Called Utah Array, these implants are also used in several dozen human patients in brain-machine interface applications that allow them to control objects in their environment, which is particularly useful for patients who are paralyzed.
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I scratch you, you scratch me
In their work, the researchers placed the implant in the brains of two male macaques who each shared their enclosure with a female. The two partners were in a relationship and knew each other very well.
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Two rhesus macaques delouse and groom each other in Bundi, India.
The implants were placed in the brain using neurosurgical techniques similar to those used in humans, with the same ethical standards.
We were able to record the neural signature of the widest range of behaviors we have ever been able to study in primates. And when I say the primate, I include the human, A wise man.
The researchers identified a total of 24 natural gestures, which included the actions of feeding, moving, arguing, fighting, mating and grooming (grooming) mutually, a very important typical behavior in the macaque that helps maintain relationships and alliances.
The grooming, it’s the equivalent of giving yourself a massage in humans. This means: you are important to me, I take care of you, notes the researcher.
Using a system of cameras, small wireless data loggers, implants and advanced artificial intelligence techniques, we have been able to quantify behaviors and see exactly how long they take and the other for different tasks, including grooming.
For the first time, researchers have collected information on the activity of hundreds of individual neurons in the macaque brains.
These neurons were located in two regions (infratemporal cortex and prefrontal cortex) of the brain that represent relatively opposite ends of the information processing pathway. One of them manages the intermediate stages of visual processing and the other controls the contextual information that supports thinking, such as decision-making.
Initially, the researchers believed that these two areas would exhibit very different responses to different behaviors, but instead they noticed similar activity.
The activity of the neurons was clearly separated and structured according to the monkey’s behavior and its social context. This activity tracked what the monkey did, who it did it with, and how long it interacted.
The researchers noticed that if one partner spent more time grooming the other on certain days, over a period of about a week, the two made up the inequality.
Thus, male and female partners demonstrated almost perfect reciprocity in grooming. It’s incredible! This means that macaques are able to keep a record in their brain of what they owe each other… just like humans.
A cerebral register
Thanks to the implant, researchers were able to see how neural networks maintain this register of social interactions. In other words, they were able to identify the neurons that encoded exactly when partners calculate what they owe and expect from each other.
We have access to typical neural representations of actions. […] Basically, these neuronal representations are positioned in complex mathematical spaces which are organized along an axis in time… And we have possibly identified the register which allows humans to be egalitarian in the face of these congeners.
Empathetic like a macaque
In another part of the experiment, the researchers looked the males directly in the eye – a behavior deemed aggressive by the monkeys, who immediately became aggressive when left alone. However, in the presence of their female, this reaction was more moderate.
According to the researchers, this shows the effect of the presence of a social ally. Then, when a researcher looked the female directly in the eyes – the threat being addressed to the female rather than the male – the latter reacted strongly as if the threat was addressed to him. According to Dr. Tremblay, this reaction reflects a certain capacity for empathy.
Understanding to repair
The neuroscientist explains that the ultimate goal is to fully understand the neural circuits responsible for social interactions in primates to eventually better understand what is happening in the human brain. Particularly when these circuits do not function properly as, for example, in the case of autism or Alzheimer’s.
To repair these dysfunctions, we must first understand how the brain machine works, notes Dr. Tremblay.
The brain generates all our behaviors. It is he who allows us to move, to think. It is also he who determines our personality.
In the current state of knowledge, we have very little idea of certain fundamental principles of brain functioning, says the man who believes that understanding the details of the brain represents the next frontier in science.
Restore faulty circuits
These results therefore reveal the existence of a highly distributed neurophysiological register of social dynamics, a potential computational basis supporting community living in primate societies, including our own.
This work does not make it possible to establish whether the neurons observed are the source of social behaviors and what their dysfunction could mean. In other words, it was not possible to establish a cause and effect link.
Sébastien Tremblay is now imagining a next step that would make it possible to study defective neurological circuits and the means to restore them.
In humans, would certain pathological traits appear like psychopathy or personality traits like selfishness?
One thing is certain, he says, it is impossible to solve problems related to social dysfunction if we do not understand how the neurons in the brain actually allow these complex behaviors to occur.
Dr. Tremblay will refine the work carried out in the United States in a laboratory – currently being created – at the CERVO research center in Quebec which, he hopes, will make it possible to identify the causes of these behaviors using very advanced methods. manipulation of brain activity, such as optogenetics, a technique now adapted to the primate brain.
We use light to be able to precisely control not just a region of the brain, but a subgroup of neurons inside the brain, enthuses the researcher. This is another level of precision that does not exist in psychiatry or neurology.
The researcher reminds us that we are at the start of the process. You must first understand how the machine works, then you can repair it. He still hopes that his work will have important implications in neurology and psychiatry during his lifetime.
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