Monkeys have social lives, too, and watching how their brains process social cues is helping scientists better understand human social behavior and autism.
Little is known about how the human brain evaluates social information and uses it to manage behavior, notes a team of researchers at Duke University Medical Center in Durham, N.C. Even less is known about what goes wrong with this process in people with autism, a social/learning disorder that affects more than one million Americans.
"Our prior studies described how social attention of rhesus monkeys is similar to humans -- motivated by status and sex, and sensitive to the attentive states of other individuals," Michael Platt, an associate professor of neurology at Duke, said in a prepared statement.
In this new study, he and his colleagues found "that the parietal cortex, which plays a critical role in guiding attention, becomes active according to the social value of images seen and ultimately enables the behavior of the animal."
In this and previous studies, the monkeys were given juice rewards to look at different images. They would forego a reward of juice to see positive images: the hindquarters of a female, for example, or the face of a dominant monkey. But they had to be "paid" more juice to view negative images: a lower-ranking monkey or a simple gray square.
"This tells us that the monkeys chose to look at images that carried valuable social information for guiding behavior. At the same time, we monitored the activity of the neurons and noticed that the firing pattern matched the behaviors we saw," Platt said.
The firing rate of neurons in the parietal cortex increased as the monkeys viewed more positive images or received more juice.
"We interpret these results to mean that the activity of the neurons provided us with information about the value of choosing one image over another -- regardless if the reward is an expected social reward or juice," Platt said.
However, the neurons in the parietal cortex did not fire when the monkeys were shown the images but didn't have to make a choice about which image to view.
"To decide between apples and oranges or between looking at an attractive female or getting a drink, the brain must evaluate these objects in a way that permits direct comparison," Platt said. "Our research found that by the time value signals have reached the parietal cortex, they are already translated in a way that enables comparison and decision-making."
This research, published in the journalCurrent Biology, improves understanding of how a normal brain reacts in social situations and guides behavior. The research also provides possible insights into autism. People with the disorder have social behavior disabilities and often have trouble looking at other people.
"Monkeys are motivated to look at some individuals and not at others. We demonstrated that this social motivation to look at others is mediated by neurons in the parietal cortex. It's possible that deficiencies in the way 'social' areas of the brain communicate with 'attention' areas of the brain may be corrupted in autism," Platt said.