A Dartmouth study challenges the conventional view that the amygdala—the two-sided structure deep in the brain involved in emotion, learning, and decision making—is simply the brain's primitive "fear center," reflexively driving us to avoid the things we fear, from high places and tight spaces to spiders and large crowds.
The researchers report in Nature Communications that the amygdala is far more complex, acting as a sophisticated arbiter to help the brain choose between competing strategies for learning and decision-making.
"Historically, the amygdala has been studied from the perspective of fear learning, and it has been generalized to reward learning," says Jae Hyung Woo, a PhD candidate in the psychological and brain sciences and the study's first author. "Our main hypothesis was that it must have other functions given its extensive connections to the rest of the brain."
The amygdala's other functions seem to surface under uncertainty, when the brain is faced with two kinds of learning strategies in pursuing a reward. In the study, the researchers give the example of brewing a cup of coffee with an unfamiliar machine.
Under an action-based approach, you could try what you did the last time you operated a similar machine and press the button that worked before. Under a stimulus-based approach, by contrast, you could focus on a defining feature, like the machine's blinking light, and select that feature.
"People have labeled the amygdala as an emotional fear system, but there is nothing really primitive in the brain, even when you talk about this area," says Alireza Soltani , the study's senior author and associate professor of psychological and brain sciences at Dartmouth.
"The key distinction is whether learning should be tied to a motor action or the identity of the stimulus," Soltani says. "Action-based learning involves considering the specific motor movements that can lead to a reward, while stimulus-based learning can be more flexible because it allows you to evaluate and select a desired stimulus without immediately considering the actions needed to get there."
Because these two learning modes happen simultaneously, the researchers hypothesized that there should be a region in the brain that mediates between them to choose the path most likely to lead to the better outcome. A damaged amygdala appears to disrupt this mediation process, the researchers found, suggesting that it plays this critical role.
