Some memories seem seared into our brains, while others are fleeting wisps of recollection. What affects the strength and duration of memories?

One thing that helps make a memory robust is if it has strong emotional content: you probably still remember your first kiss, or where you were when you found out that a close family member had passed away. This happens because of the amygdala, which brain imaging studies have shown is activated by emotional events. The amygdala boosts memory encoding by enhancing attention and perception, and can help memory retention by triggering the release of stress hormones, such as adrenaline and cortisol, to boost arousal.

  QBI researchers have discovered that bad experiences particularly enhance memory formation about places, and suggest this may serve as a cue to avoid potential threats.

While memories of a stressful event can be enhanced, stress tends to have negative effects on memory storage for events that coincide with, but are not the direct cause of, the stress. Stress also alters the way that our brain processes information, changing from a flexible, holistic approach to more rigid stimulus–response associations. This can change the nature of the memory stored, as well as what we recall under stress.

Sleep is important for memory formation

Sleep is another important factor for memory storage. During sleep, the hippocampus and neocortex take part in a carefully choreographed dialogue in which the hippocampus replays recent events: the same hippocampal neurons active during an experience become activated again during slow-wave sleep, over and over in a time-compressed manner, helping to update the neocortex as to what needs to be stored. This replay only occurs during sleep, so if  you’re skimping on sleep, you aren’t letting your brain consolidate memories.