Optogenetics makes important discovery about social interactions

Seeking to further understand how the prefrontal cortex contributes to social behavior, a team of researchers at the Princeton Neuroscience Institute (PNI; Princeton, NJ), led by assistant professor of psychology Ilana Witten, discovered that in mouse brains, social and spatial learning are inextricably linked. Their findings could pave the way to treatments for disorders that have social behavior deficits, such as autism, schizophrenia, and dementia, she says.

Most previous research on social behavior has focused on the brain’s circuits for hardwired behaviors, like aggression, sex, or mothering. Finding a neural substrate for social learning provides a different perspective into social behavior, with possible relevance to disorders such as autism, which are thought to involve abnormalities in the same brain circuitry studied in this work.

In the research team's experiments, two mice were given a chance to socialize in a cage that limited the mobility of one of the mice (the "social target"), so the test mouse could choose whether or not to go to the target for friendly behaviors like sniffing and grooming. Later, the test mouse was reintroduced to the test cage. When the researchers used optogenetics, which involves the use of light to control neurons, to inhibit the key social-spatial pathway they had identified in the brain, the test mouse wandered freely through the space. When they didn't inhibit that circuit, the test mouse preferred to spend time where it remembered socializing with the other mouse.

"Social interactions are some of the most rewarding interactions that mammals have," Witten says. "They drive all sorts of different forms of learning, the simplest being what we found here: spatial learning, contextual learning."

Witten and her research team performed optogenetic experiments with the mice to isolate precisely which circuits of the brain are involved in social-spatial learning. Previous research had identified that the prelimbic cortex, part of the prefrontal cortex, has three “downstream” channels into the nucleus accumbens, the amygdala, and the ventral tegmental area. The researchers determined that only the pathway between the prefrontal cortex and the nucleus accumbens is linked to the social-spatial learning they observed.

Next, the researchers plan to examine how the neural substrates of social and spatial learning differ in mouse models of autism. This may shed light on the question of whether autism stems from physical causes or deficits in social learning.

Full details of the work appear in the journal Cell.