Washington: A small structure in the brain generally associated with negative behaviours, specifically fear, can also influence positive social functions such as kindness, a new study has found.
The study on amygdala, a small structure at the front end of the brain's temporal lobe, could have implications for people with autism, schizophrenia or anxiety-related disorders.
Researchers at the University of Pennsylvania, Yale University and Duke University in US looked at the social behaviour of rhesus macaques, a non-human primate species.
The researchers incorporated a task they developed four years ago as a way to observe how animals make beneficial decisions, a process they described as a reward-donation task.
"We have an actor monkey and a recipient monkey. The actor monkey learns that different-coloured shapes on the screen are associated with a reward that can be delivered to himself, to the monkey next to him, to both or to nobody at all. They learn that over a couple of weeks," said Michael Platt from University of Pennsylvania.
Once the researchers determined the monkeys understand the task, based on how quickly the macaques responded to the rewards, they then presented the actor monkey with choices and their accompanying potential rewards.
The primates could keep the reward (in this case, a squirt of juice), share it, give it away or let it go to waste. "Generally our actor monkeys prefer to reward the other monkey rather than let it go unclaimed," Platt said.
"They are more likely to give to those they're more familiar with, and also to monkeys subordinate to them. The social relationships shape how prosocial the actor monkeys are," he added.
The researchers recorded the neural activity of the amygdala of each animal, to note any correlations between what was happening in the brain and their outward actions.
They found that neural activity in the amygdala reflected the value of the recipient's reward in the same way it reflected the value of the reward for the actor.
The scientists could predict when actors would give rewards to the recipients based on these neural responses.
When oxytocin was introduced, behaviours changed rapidly. Oxytocin is a hormone linked to social bonds between individuals.
In animals, it has been shown to create strong ties between mother and offspring, as well as male and female partners in certain monogamous animals. In the study, the monkeys receiving oxytocin became more willing to give to other monkeys and paid more attention to them after offering the rewards.
"Just like humans, the stronger these bonds the monkeys have, the more successful they are," Platt said.
The findings were published in the journal PNAS.
