As [Salk Institute postdoctoral researcher Hao] Li and his team reported recently in Nature, the difference between memories that conjure up a smile and those that elicit a shudder is established by a small peptide molecule known as neurotensin. They found that as the brain judges new experiences in the moment, neurons adjust their release of neurotensin, and that shift sends the incoming information down different neural pathways to be encoded as either positive or negative memories.
The discovery suggests that in its creation of memories, the brain may be biased toward remembering things fearfully — an evolutionary quirk that may have helped to keep our ancestors cautious.
The ability of the brain to record environmental cues and experiences as good or bad memories is critical for survival. If eating a berry makes us very sick, we instinctively avoid that berry and anything that looks like it thereafter. If eating a berry brings delicious satisfaction, we may seek out more. “To be able to question whether to approach or to avoid a stimulus or an object, you have to know whether the thing is good or bad,” Hao Li said.
Memories that link disparate ideas — like “berry” and “sickness” or “enjoyment” — are called associative memories, and they are often emotionally charged.
