Millions of adults suffer from anxiety disorders where their constant worrying affects their daily lives.
Now, scientists have identified the area of the brain that controls fear, offering hope of a treatment for such disorders.
US researchers have described a 'circuit' that controls fearful memories and behaviour in the brains of mice, offering insight into how anxiety disorders may develop.
Associate professor Bo Li, who led the study at Cold Spring Harbour Laboratory (CSHL) in New York, said: 'In our previous work, we discovered that fear learning and memory are orchestrated by neurons in the central amygdala.'
It is thought it could be controlled by a cluster of neurons that form the PVT, or paraventricular nucleus of the thalamus.
This region of the brain is extremely sensitive to stress, acting as a sensor for both psychological and physical tension.
The researchers were interested in whether PVT plays a role in learning and remembering fear in mice.
Professor Li said: 'We found that the PVT is specifically activated as animals learn to fear or as they recall fear memories.'
The researchers found that neurons from the PVT extend deep into the central amygdala, and that disrupting the connection significantly impaired fear learning.
They believe that because the link between the PVT and the central amygdala is a critical component of fear learning, drugs could be used to target it in a bid to treat anxiety disorders.
Building on the finding, the scientists examined data taken from people with post-traumatic stress disorder (PTSD) to identify chemical messengers that might connect the PVT and central amydala.
They focused on a molecule called BDNF that's been linked with anxiety disorders and is known to play an important role in stimulating the birth of new neurons, as well as new connections between neurons.
Previous studies have shown that patients with anxiety disorders have mutations in BDNF, suggesting that it might have a role in fear learning and memory.
Using mice, the researchers investigated whether BDNF plays a role in fear and affects the connection between the PVT and central amygdala.
They found that the presence of BDNF in the central amygdala activates the brain region's neurons, causing mice that had not been frightened, to react fearfully.
It also caused the formation of long-term fearful memories, they said.
Professor Li explained: 'We established that this is a regulatory circuit that controls fear in mice: BDNF is the chemical messenger that allows the PVT to exert control over the central amygdala.'
He added: 'Our work provides mechanistic insight into a novel circuit that controls fear in the brain, and provides a target for the future treatment of anxiety disorders.'
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