Special cells in the brain allow animals to overcome fear and anxiety by recalling memories of similar situations when they were unafraid, according to new research.
The finding could lead to new drugs for helping people with anxiety-related conditions such as post-traumatic stress disorder, scientists say.
Previous work had suggested that a part of the brain called the amygdala—an almond-shaped mass of cells deep in the brain—plays an important role in this process, known as fear extinction.
(Related: "Without Gene, Timid Mice Turn Into Daredevils" [November 29, 2005].)
This is what allows soldiers, for example, to learn that some noises they hear on the battlefield might not represent immediate threats when they return home.
Researchers for years have had difficulty determining which of the dozen or so clusters of cells that make up the amygdala is directly responsible.
Now, using a technique that selectively eliminates brain cells, neuroscientist Denis Paré and colleagues have revealed that cells called intercalated (ITC) neurons are crucial for overcoming fear.
"The available data indicates that one does not unlearn fear but instead learns not to fear the threatening stimulus in particular contexts," said Paré, of Rutgers University in New Jersey.
Frozen in Terror
Paré and colleagues demonstrated the importance of ITC neurons by training rats wandering free in cages to associate a certain sound with a mild electric shock to their feet.
This conditioning taught the rats to be afraid of the sound, and they would freeze in place for a few seconds whenever they heard it.
Next the researchers presented the tone without the shock so the rats had memories of hearing the sound without cause for fear.
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