Immune cells in the brain act as gatekeepers that stop you from forgetting your fears by physically eating the forgetting circuitry.
Microglia are the brain's resident immune cells, usually known for cleaning up debris and fighting infections. This study found that they also play a dark role in trauma by targeting the specific synapses used to overwrite fear memories. When the brain tries to form an extinction circuit to calm a fear response, these cells move in and destroy those connections. This process ensures that the original fear memory stays dominant and protected. Targeting these specific immune responses could lead to new ways to treat post-traumatic stress disorder and other anxiety-related conditions.
Microglial pruning of extinction-ensemble synapses preserves fear memory
bioRxiv · 10.64898/2026.05.05.722833
Fear extinction suppresses learned fear without erasing the original memory, yet how competing fear and extinction ensembles are selectively updated remains unknown. Here, we show that microglia preserve fear memory by selectively editing extinction-ensemble synapses during retrieval. In medial prefrontal cortex, microglial processes, but not somata, expand, ramify, and tighten their engagement with extinction-ensemble dendrites and spines, where they preferentially engulf excitatory postsynapti