Still Waters.

The prefrontal cortex is that part of the brain that mediates emotional response to stimuli.

The prefrontal cortex joins with the amygdala, which governs how short-term memory gets converted into long-term memory.

The amygdala also provides the association between a strong emotional reaction and how that reaction gets stored in long-term memory.

When the prefrontal cortex and the amygdala dysfunction, the checks and balances in terms of memory association can be thrown off.

In other words, you can have either off-the-charts emotional reactions to events or no reaction at all.

It is the emotional "memory" of an event that allows it to be recorded into long-term memory.

Source : Mayo Clinic