“Why do our most emotionally intense experiences—times when we were livid with anger, petrified with fear, or in shock from witnessing something terrible—seem to be indelible in memory? The answer to that question is fundamental to the very reason we evolved the capability to remember: our memories hold the key to our survival.

“As we've learned, the brain is constantly prioritizing what it thinks is important and letting us forget what isn't. So, it makes sense that we tend to remember the events associated with intense emotions, but that's only part of the story. Emotions, the conscious feelings we experience based on myriad combinations of internal and situational factors, are central to the human experience, but in and of themselves they aren't necessarily important for our survival—feeling a little guilty or embarrassed isn't going to put food on the table or a roof over your head. Rather, the critical influence of emotional experiences on memory has to do with what neuroscientist Joe LeDoux calls survival circuits.

“Our emotions, as well as the actions and choices they influence, are shaped by basic survival circuits in the brain that motivate us to avoid threats, find sustenance, and reproduce. When these circuits go into overdrive, we tend to experience intense emotions, such as elation, lust, panic, anxiety, or disgust. It makes perfect sense that these are experiences we remember most vividly. Events that intensely activate our survival circuits are worth remembering because they usually provide valuable information that we can use in the future to stay safe, thrive, and reproduce. We might not have survived as a species if our cave-dwelling ancestors hadn't found encounters with saber-toothed tigers to be particularly memorable.

“When a survival circuit in the brain gets revved up, say by the terror of a face-to-face encounter with a predator, or the joy of holding. your child in your arms for the first time, your brain gets flooded with neuromodulators. Neuromodulators are chemicals that influence the functioning of neurons, but they don't simply increase or decrease neural activity. Neuromodulators have more complex effects that fundamentally change how neurons process information. Some neuromodulators are like the hot sauce on your tacos-they change the flavor, add heat, and cause us to sit up and pay attention. Neuromodulators also promote plasticity, meaning they enable significant, long-lasting changes in the connections between neurons in the cell assemblies that are activated when we learn something new.

“Noradrenaline (also known as norepinephrine) is one well-studied neuromodulator that influences how we learn and remember. You've probably heard of the fight-or-flight response. When we experience threats, the adrenal glands mobilize us into action by pumping out adrenaline, which raises our heart rate, blood pressure, and breathing rate. Noradrenaline, in turn, is released all over the brain. Adrenaline and noradrenaline are the chemical costars of the fight-or-flight response, contributing to the feelings of arousal and immediacy you might experience if you go bungee jumping or get into a shouting match with a driver who cut you off.