Fear and anxiety are ancient and useful emotions. These deeply-encoded feelings help keep us safe—for instance, when our “fight-or-flight” response shapes how we respond to dangerous situations. What is not useful, however, are what the National Institute of Mental Health describes as disproportionate or prolonged fear responses that wear down a person’s ability to navigate daily life.
Statistics reveal that approximately 18% of adults living in the United States experience ongoing, unhelpful fear and anxiety. Whether they know it or not, they’re living with an anxiety disorder. Anxiety disorders include a wide range of conditions, all of which stem from mutated fear response.
How Do Brains Process Fear?
To better understand how our brains respond to fear, scientists have studied animal models with brain architecture similar to humans. This has uncovered crucial information about the how—and where—the brain processes fear. A part of the brain called the amygdala plays a central role in fear processing, while memories of emotional events form primarily in a different area called the hippocampus.
Researchers at the University of California-Irvine (UCI) set out to investigate how the amygdala and the hippocampus communicate when a person experiences fear.
Measuring the “Fear Response” in Real Time
To examine the neural pathways that human brains use to process fear and anxiety, the team of scientists, led by Dr. Jack Lin, a professor of neurology at UCI, surgically inserted electrodes into the amygdala and hippocampus of study participants. All participants had a form of medication-resistant epilepsy, and the electrode placement procedure was done primarily as part of a clinical evaluation of seizure activity. For Lin and his colleagues, it also offered a unique opportunity to precisely measure brain activity.
While participants watched scenes from horror movies, the researchers recorded their neural activity. “Deep brain electrodes capture neurons firing millisecond by millisecond,” explains first author Jie Zheng. This data reveals how human brains respond to fear “in real time,” says Zheng.
The researchers found that when a human confronts something frightening, the amygdala signals the hippocampus. This pattern of activity occurred only during the frightening movie clips, not during peaceful scenes. Lead author Lin says that study offers “direct evidence that the amygdala first extracts emotional relevance and then sends this information to the hippocampus to be processed as a memory.”
How to Treat the Source of Anxiety
Lin and the team believe their work could radically shift the way we treat anxiety disorders. The drugs currently used to treat anxiety bind to large areas of the brain, meaning that any relief they offer comes with side effects, which are tolerable for some, and intolerable for others. Lin and his fellow researchers hope in the future, their work and studies like theirs can be used to “target and manipulate the precise amygdala-hippocampal circuit involved in processing negative emotions.”
One particularly compelling finding from a separate investigation using deep brain electrodes to examine the amygdala and hippocampus. This work was done by Christina Zelano, an assistant professor of neurology at the Northwestern University Feinberg School of Medicine. Zelano and her team found that the way we breathe affects communication between the amygdala and hippocampus. Zelano says this may help to explain why breathing exercises and meditation can help to alleviate anxiety. You can learn more about how that works here.