One of animals' evolutionary advantages is that they can learn from experiences of others instead of all undergoing those personally. A new study published on Thursday in the journal Cell reported the neural mechanism underlying this ability called observational learning.
Kay Tye, an associate professor of brain and cognitive sciences in Massachusetts Institute of Technology (MIT), and her colleagues identified the brain circuit that is required for this kind of learning.
This circuit, which is distinct from the brain network used to learn from firsthand experiences, relies on input from a part of the brain responsible for interpreting social cues.
Previous brain-scanning studies in humans have suggested that two parts of the brain known as the anterior cingulate cortex (ACC) and basolateral amygdala (BLA) are active when we learn by watching others.
The ACC is involved in evaluating social information, among other functions, and the BLA plays a key role in processing emotions. However, it was unknown how these regions interact to learn from others' experiences.
The MIT team investigated what happened in the brains of mice as they observe another mouse receiving electric shocks paired with a cue such as a tone or light.
The researchers found that when mice that had watched this process heard the cue one day later, they froze in fear, even though they had not experienced any shocks during the conditioning.
The researchers recorded electrical activity in both regions as the mice watched the fear conditioning process, then performed a new type of analysis called neural trajectory analysis, which reveals how neurons change their firing rates as a behavior is learned.
The analysis has shown that the ACC becomes much more active as the mouse witnesses another mouse's experience and then relays information about the experience to the BLA, which uses it to form an association between the cue and the shock.
"The anterior cingulate is transmitting that there is important information to extract from the demonstrator," Tye said. "It's translating socially derived information and sending it to the BLA to assign predictive value there."
The researchers then identified specific neurons in the ACC that connect directly with neurons in the BLA.
When the researchers blocked the ACC-to-BLA connection in mice that were receiving shocks paired with a tone, there was no effect on the observer mouse's ability to connect the cue with the shock.
The researchers also showed that the ACC is necessary for more general types of social behavior, such as interacting with a nonthreatening juvenile mouse.
Tye said the team was now hoping to study whether this circuit was also active when mice learned from other kinds of experiences, such as watching another mouse earn a reward for performing a particular task.
"So much of what we learn day-to-day is through observation," she said. "Especially for something that is going to potentially hurt or kill you, you could imagine that the cost of learning it firsthand is very high. The ability to learn it through observation is extremely adaptive, and gives a major advantage for survival."