Rapid reacquisition of fear to a completely extinguished context is replaced by transient impairment with additional extinction training

A series of experiments studied reacquisition of fear reactions to a completely extinguished context. Reacquisition was rapid when reconditioning occurred as soon as the fear reactions were completely extinguished, showing that the original conditioning was intact. However, when reconditioning occurred after massive extinction training, fear reactions were depressed but then recovered across a long retention interval. This recovery was due to reconditioning and was similar to that produced by conditioning a massively preexposed context. These results show that massive extinction converts a potentially dangerous context into one that is merely familiar.