The common term “extinction” may be the wrong word for what happens when we overcome our learned fears, says Andreas Lüthi of the Friedrich Miescher Institute in Basel, Switzerland. He suggests “active suppression” instead, based on research he and colleagues published in Nature online on July 11.
Studying mice, they discovered that one group of neurons in the amygdala is involved in suppressing established fear responses—and another, distinct group can refresh or restore these responses. Like flipping a switch, by selectively activating one or the other group, the researchers could suppress or trigger fearful behavior in the mouse.
“The new learning [repression] is on top of the old learning [trained fear response], and it uses very similar molecular mechanisms,” Lüthi said during a press conference at the Forum of European Neuroscience meeting in Geneva on Monday. So a mouse that has “unlearned” its fear response to a tone, for example, has not extinguished it completely—and it might be triggered in a new situation.
“It’s really a breakthrough discovery to understand how to get rid of fear, but also what may cause its relapse,” said Casten Wotjak of the Max Planck Institute of Psychiatry in Munich. Fear is one of our most basic responses and has been relatively stable in evolutionary terms. So what happens in people’s fear pathways likely parallels what happens in mice’s fear pathways, Wotjak says.
Their research suggests why treatments such as exposure therapy, used to help people overcome phobias, may not always work. People might overcome their fear to a specific type of height, for example, or overcome it while in their doctor’s presence, but another, similar setting could trigger their fear switch back on. In this case, “extinction” would be preferred.