A new study has found specials cells in the brain that allow animals to overcome the feelings of fear and thus increase bravery.
According to scientists, the results can lead to new drugs for helping people with anxiety-related conditions such as post-traumatic stress disorder.
Using a technique that selectively eliminates brain cells, neuroscientist Denis Pare 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," National Geographic News quoted Pare, of Rutgers University in New Jersey, as saying.
The research team 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.
The following day the team used a targeted drug to render ITC neurons useless in half of the trained rats.
When presented with the tone a week later, rats with intact ITC neurons remembered that the sound no longer signaled an impending shock and continued to act normally.
The animals missing ITC neurons, however, remained afraid of the tone. They froze whenever they heard it, anxiously anticipating a jolt that never came.
The findings support the theory that ITC cells play an important role in forming and expressing so-called extinction memories-remembered moments of safety that help overcome fear.
The research is detailed today in the online edition of the journal Nature.