The Drew lab published a paper in Nature Neuroscience entitled "Distinct hippocampal engrams control extinction and relapse of fear memory".  This work demonstrates that the hippocampus, a part of the brain essential for memory, generates memory traces of both fear and extinction, and competition between these hippocampal traces determines whether fear is expressed or suppressed.  This work has important implications for understanding the potential cause of disorders, like anxiety and PTSD, and they can also help us understand potential treatments.

Lacagnina AF, Brockway ET, Crovetti CR, Shue F, McCarty MJ, Sattler KP, Lim SC, Santos SL, Denny CA, Drew MR.  Distinct hippocampal engrams control extinction and relapse of fear memory.  Nature Neuroscience. 2019 May;22(5):753-761

https://www.newsweek.com/brain-fight-fearful-memories-extinction-neurons-ptsd-1381662
 
https://www.popsci.com/extinction-neurons-trauma-fear-memory