The crowd of scientists was thinner for Elizabeth Phelps’ special lecture, “Changing Fear,” on the final day of the Society for Neuroscience annual meeting. But her work was among the most interesting I heard presented, in part because she studies humans as well as other animals.
Phelps’ main point was that the fear response can change, sometimes for the better. “Something that is fearful today may be rewarding tomorrow,” she said in her introduction.
Humans, like other animals, can be conditioned to associate a tone with a mild shock. We will then display a fear response when we hear the tone. In the brain, it’s the amygdala that is responsible for the physical expression (such as sweating, increased blood pressure or a quickening pulse) of a learned fear response.
Humans can also learn a fear via instruction—simply from being told that there may be a shock, for example—or via observation, such as by watching someone else receive a shock after hearing a tone. Understanding this, researchers can develop models of fear learning in complex, uniquely human social environments, Phelps said.
These models will help explain what Phelps called a critical question regarding human fears: how to diminish or extinguish them. For example,exposure therapy, which includes learning that a previously fear-inducing stimulus is safe, is a successful model, she said.
In animal models of what’s called fear extinction, the response in the amygdala decreases because it is inhibited by another region, the ventromedial prefrontal cortex, which Phelps said is necessary for keeping the fear from returning later. One interesting facet of this area of research is that humans were able to decrease their own fear response by thinking of something calming when shown a fear-related stimulus, with corresponding variations in brain activity.
Phelps and her colleagues are now studying how to erase a fear memory altogether, perhaps by disrupting the reconsolidation of such a memory. Their theory is that when we retrieve a memory, it may be “fragile,” offering an opportunity to influence or change it. Studies in humans have offered evidence that extinction training during reconsolidation can prevent the reinstatement of fear.
Still, “there are many things we don’t know at this point,” Phelps said. Among the more intriguing questions are whether such extinction training might affect not just conditioned fear but complex emotional memories, and, if so, whether such approaches might help treat anxiety disorders.
Much more research lies ahead. Look for fascinating insights about emotion and memory along the way.