The brain's social circuit

Why first impressions last: the brain circuits that control how a rat responds to a newcomer...
17 April 2015

Interview with 

Alex Tendler, Haifa University


When you meet someone new, what goes through your mind? And is it reallyRats socialising true that first impressions last? Working with rats, Haifa University's Alex Tendler argues that the answer is definitely yes. And your brain probably puts itself into a special pattern of neurological activity on that first encounter, and this controls how you respond and form an opinion of the individual you've just met.

Alex - We've tried to identify electrical signals in the brain during social interactions between rats and to achieve that, we implanted electrodes into rat's brain at six different regions that are related to social recognition and memory. Tiny wireless transmitters were mounted on the rat's head and the rat was subjected to meeting with other unfamiliar animals. During each encounter, video and brain signals were synchronized and could be seen in real time.

Chris - Can you therefore plot a sort of time course - which brain area activates first and then where it then sends signals to in that network of related brain structures?

Alex - The interesting thing was it was not like one after the other. It works in a synchronized manner. We found a profound rhythmic electro-activity, that reflects animal's excitement throughout brain areas, that's responsible for social recognition. It was particularly strong and synchronized in the first encounter when the rat met unfamiliar rats.

Chris - Do you think that the rhythms that you see are the product of all of these areas talking to each other, or does one of them act like a metronome and make all of them beat the same tune?

Alex - I think that special communication protocol synchronizes between relevant brain regions and tells the brain how and in what frequency to operate.

Chris - And so would your hypothesis be that when you introduce an animal to a new social situation, this particular pattern of brain activity is elicited, which then puts these different brain components in this network into a very receptive or aroused mode so that they're paying attention to what's going on socially?

Alex - Yes. It's alike for different excitements. There are different brain states and different communication protocols. That's what we see because when we check the same experimental protocol with an inanimate object, instead of a rat, we didn't find such synchronization, despite the fact that from behavioral point of view rats show the same interest to the objects too. When we tried different feelings like fear, we also found synchronization between the regions related to memory but in completely different frequencies.

Chris - So this appears to be this pattern of brain activity of a certain rhythm unique to animals that are having a social engagement.

Alex - Exactly. And we found that this synchronous brain activity continues even after the end of social encounter, meaning that the brain enters into a kind of social state.

Chris - But then, if you reintroduce the animal that's just produced that impression, do you get the same big surge of activity again or the next time are they less excited to see each other?

Alex - It's much, much lower. They are less excited.

Chris - What about if you repeat the experiment with an animal that's not socially active. So, if I put in a sleeping rat. Would it respond in the same way? Can it recognize there is another rat here or is this purely down to active behavior on the part of the individual that's being met?

Alex - Yeah. We tried it with anesthetized animals also, and there is no connection with the behavior of the animal that we exposed to. It's the animal and not the object.

Chris - Do you think that what you've discovered here has implications for human situations? Because there are some individuals who have certain conditions, and I'm thinking Asperger's type individuals, who have difficulty relating to other individuals socially. Do you think that there are implications from this work for understanding what's going on with them?

Alex - Yeah. I think that here for the first time, we showed that there are different feelings influencing memory formation and we show that there is kind of communication protocol between brain areas. And it is known that problems like Asperger and the other autistic spectrum disorders there are problems with communication between different brain regions. So, it can help us to recognize the problems and maybe to treat them.


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