This 2014 Brazilian rodent study provided more information on the workings of the hippocampus. The researchers measured the effects of re-experiencing a fear within a specific context:
“Within a restricted time window, a brief exposure to a novel environment enhances the extinction of contextual fear.
The enhancement of extinction by the exposure to novelty depends on hippocampal gene expression..on hippocampal but not amygdalar processes.”
http://www.pnas.org/content/111/12/4572.full “Hippocampal molecular mechanisms involved in the enhancement of fear extinction caused by exposure to novelty”