Pointing to the change in amygdala activity, which is central to the brain's system of storing and
recalling fearful memories (see How Fear Works to learn about this process), the researchers say the memory was not simply disconnected from fear, but that it was actually erased in its entirety.
They found that while the mice could not
recall those
memories in response to natural cues, such as being placed in the cage where a
fearful event took place, the
memories were still there and could be artificially retrieved using a technique known as optogenetics.