Whether it’s fending off a saber-tooth tiger or delivering a wedding toast, fear responses are hard-wired in our brains, compelling us either to flee from the situation or confront it head-on. But in recent years, scientists have established a third response: freezing. And a new study reveals how it’s integrated into the brain’s overall circuitry.
The part of your brain most responsible for feeling afraid is the amygdala. When threatening stimuli hits the back of your eye, signals are sent straight to the amygdala, which uses its bank of conditioned responses to quickly file away the present situation into any number of folders. Prior research has shown that people with lesions on parts of their amygdalae don’t produce a fear response. Such was the famous case of S.M., a female patient dubbed the “woman with no fear.” A severely damaged amygdala rendered her unfazed by snakes, horror films, haunted houses, and real-life knife attacks.
When we encounter frightening situations, we either engage in a fight response, flight response, or freezing response. Researchers have long understood the first two, but the third has remained something of a mystery. Now a team of scientists from the University of Bristol has discovered the pathways that regulate freezing responses, and their results, they argue, could be instrumental in helping people overcome certain disorders.
“Our work introduces the novel concept that the cerebellum is a promising target for therapeutic strategies to manage dysregulation of emotional states such as panic disorders and phobias,” explained Systems Neuroscience Professor Bridget Lumb in a news release.
Lumb and her colleagues examined a crucial part of the cerebellum involved in freezing response, the periaqueductal grey (PAG). It sits beneath the cerebrum, along the spine, and highly regulates animals’ sense of relaxation or tenseness. When researchers investigated where these pathways led, they found themselves in a separate region, known as the pyramis. Specifically, when innate and learnt threatening situations were at play (those being either survival modes or aversions to certain noises), the pyramis lit up.
The upshot, the team found, was that the pyramis acts as a junction for a number of survival-related responses. Many of these fear responses are emotional in nature, meaning that somehow tapping into the pyramis’ regulatory abilities could lessen the severity of panic disorders, phobias, and anxiety.
According to the National Institute of Mental Health, nearly nine percent of the U.S. adult population suffers from a phobia, and more than a fifth of those are classified as “severe.” Anxiety disorders feature even greater prevalence, at more than 18 percent of the U.S. population and 22.8 percent classified as “severe.” Developing treatment options that employ brain behavior specifically and directly could help offset these debilitating trends, the researchers argue.
“There is a growing consensus,” said Dr. Stella Koutsikou, researcher in the School of Physiology and Pharmacology and the study’s first author, “that understanding the neural circuits underlying fear behavior is a fundamental step towards developing effective treatments for behavioral changes associated with emotional disorders.”
Source: Koutsikou S, Crook J, Earl E, et al. Neural substrates underlying fear-evoked freezing: the periaqueductal grey?cerebellar link. The Journal of Physiology. 2014.
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