the prefrontal cortex reduces fear by inhibiting 
the amygdala, a hub of fear memory deep in the brain. 
When the rats heard the tone without the shock several times 
they learned not to be afraid -- a process called
extinction or sefety learning.  

The original fear association was not erased 
(it is important for survival) but overtaken by the new memory. 

"Our data suggest that the rats that were shown 
the tone-fear stimulus again and again with stimulation of
this area had very low fear," 
said Puerto Rico Professor Gregory Quirk. 

People with post-traumatic stress disorder 
appear to have weak activity in the prefrontal cortex of the brain,
according to the scientists. 
They believe a painless experimental technique 
called transcranial magnetic stimulation 
might help them control fear. 

funded by the National Institute of Mental Health