Our memories hold the key to our survival

I met LC while managing admissions at the Veterans Administration Day Hospital, an intensive outpatient program for veterans going through a critical time. (…) I asked her a series of questions to get an idea of ​​her emotional state and her brief answers indicated to me that she did not feel comfortable acknowledging any type of vulnerability, much less asking anyone for help. That she was talking to me at the hospital indicated that she had run out of options. She told me that she always had her nerves on edge, that she barely slept and that, when she did, she was kept awake by horrible nightmares. She had been living on the edge of the cliff and she had suicidal thoughts. I knew that she had not participated in active combat and she did not like to talk much about her time in the war, so my challenge was to gain her trust so that she would tell me some of her experiences.

(…) In the end LC revealed to me that she had been assigned to a funeral unit during her deployment in Iraq. Her job was to shroud the corpses of dead soldiers to send them back to their families (…). She vividly described the stench of death in the air and the horror of having to handle bodies dismembered by improvised explosive devices. Since her mission had concluded and she had returned home, she felt permanent anguish and was haunted by recurring memories of the corpses of fallen soldiers. Having not witnessed the fighting, it had not occurred to her or the Veterans Administration that she might have post-traumatic stress disorder (PTSD). But it was evident that her experiences in the war had exposed her to extreme trauma. The tremendous intensity of the emotions that she dealt with daily during her service did not let her live.

I wish I could say that LC's experience was an isolated case, but the majority of my patients at the Veterans Administration had some form of PTSD. While many of us are frustrated by our inability to remember the past, people with PTSD suffer precisely from the burden of remembering it too well. They experience their trauma repeatedly through flashbacks and nightmares. (…)

PTSD has both personal and social consequences. It causes high rates of alcoholism, drug addiction, unemployment and homelessness among sufferers as they attempt to battle debilitating trauma. LC's case is an extreme example, but many of us are affected by distressing memories that accompany us and that can influence our mood, our thinking and our present actions.

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This power of influence of emotions on memory is not always negative. Emotional turmoil also works in reverse. Think about when you met the love of your life or the birth of a child and you will notice the emotional intensity that permeates the most memorable experiences. But how and why do our emotions color our memory of the past? And more importantly, how do past emotional experiences affect us in the here and now? As we will see, the brain mechanisms for remembering what happened are different from those responsible for the feelings that emerge when we remember, and this distinction has important implications for our perception of the past and for the decisions we make in the future.

Why does the memory of our most intense emotional experiences, the moments in which we have felt angry, petrified by fear, or shocked by witnessing something horrible, seem indelible? The answer to that question is fundamental to understanding why our ability to remember evolved: our memories hold the key to our survival.

As we have seen, the brain continually prioritizes what it considers important and allows us to forget what is not. Hence it is logical that we tend to remember events associated with intense emotions. But that's only part of the point. Emotions, the conscious feelings we experience based on endless combinations of internal and situational factors, are central to the human experience, but in themselves they are not essential to our survival; Feeling a little guilty or embarrassed is not going to put a plate on the table or a roof over our heads. Rather, this fundamental influence that emotional experiences have on memory is related to what neuroscientist Joe LeDoux calls “survival circuits.”

Our emotions, as well as the actions and decisions they influence, are often shaped by basic survival circuits in the brain that motivate us to avoid threats, find sustenance, and reproduce. When these circuits become overloaded, we tend to feel intense emotions, such as euphoria, lust, panic, anxiety or disgust. And it is logical that these are the experiences that we remember most clearly. It is in our best interest to remember the events that intensely activate our survival circuits because they often provide us with valuable information that we can use in the future to protect, thrive, and reproduce. Perhaps we would not have survived as a species if our caveman ancestors had not found their encounters with saber-toothed tigers memorable.

When a brain survival circuit is revolutionized, for example by the terror caused by a face-to-face encounter with a predator or by the joy of holding a newborn child in your arms for the first time, the brain is flooded with neuromodulators. Neuromodulators are chemical substances that influence the functioning of neurons, although they are not limited to increasing or reducing neuronal activity. Neuromodulators have more complex effects that fundamentally change how neurons process information. Some neuromodulators are like the hot sauce on tacos: they change the flavor, add pungency, and make us sit up in our seats and pay attention. Neuromodulators also promote “plasticity,” which means that they enable significant and lasting changes in the internal connections of the neuronal assemblies that are activated when we learn something new.

Norepinephrine (also called norepinephrine) is a well-studied neuromodulator that influences the way we learn and remember. You've probably heard of the fight or flight reaction. When faced with a threat, the adrenal glands mobilize us to react by pumping adrenaline, which accelerates heart rate, blood pressure and respiratory rate. In turn, norepinephrine is released throughout the brain. Adrenaline and norepinephrine are the chemical co-protagonists of the fight or flight reaction, as they enhance the feeling of agitation and immediacy that we experience when bungee jumping or getting into a shouting match with a driver who has just cut us off.

Psychologist Mara Mather has shown that emotional activation increases our attention span and enhances our perception of highlights that are important or that stand out in some way. So this activation influences the result of the “neural choices” that determine what we will perceive, channeling resources towards the most solid candidates.

Since emotional arousal limits what we pay attention to, it would be logical to think that it will change what we remember and not just how intensely. For example, if a person is robbed at gunpoint, it will be the gun that captures your attention, possibly at the expense of noticing what shoes the robber is wearing. Just as increasing the contrast of a photograph highlights one piece of information and sends other information to the background, norepinephrine enhances the contrast of our memories and highlights the most significant details.

The effects of norepinephrine last even after the emotionally intense event has ended. For a few hours, norepinephrine triggers a burst of events in the neuronal assemblies that have remained active during the event and activates the genes that make the proteins that will end up consolidating the connections between those neurons so that the memory remains robust over time. time. If you witness a horrendous vehicle collision in front of your neighborhood supermarket, the release of norepinephrine will stimulate changes in the connections of your brain cells so that your memory of that shopping trip stays with you more than if you had left the store. without incident. This is a key reason why it is easy to forget more mundane experiences and so difficult to let go of a traumatic memory: our brain is designed to retain the events that have revolutionized us, supposedly because remembering them has value for our survival.

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