When I was little, I loved looking at those picture-filled books, even before I learned to read. I would gaze at all those drawings and colors and be enchanted. I still remember the stories my parents told me before bed; sometimes it was my dad, and sometimes it was my mom. The joy I felt in those moments was so great that even after so many years, I still hope to one day tell the same stories to my children, without even needing the books. In fact, it’s easy to remember the moments that were special in our lives, and (unfortunately...) hard to forget those we most wish to erase from our memory. Why do some of our memories stay alive for so long, while others are quickly forgotten? Let’s try to understand a little better.
External experiences reach the nervous system through the senses; thus, the first mnemonic processes are pre-conscious and occur in the sensory systems. These are pieces of information we store for a short period of time, and we are not even aware of them. However, only part of this initial information is kept in our long-term memory, while another part is quickly lost. Various studies have demonstrated the existence of memory modulatory systems capable of interfering with its storage and have found that even hormones, whose action is not always directly exerted on the central nervous system, can contribute to this modulation, especially those involved in emotional phenomena, such as those related to stress.
Stressful events activate the amygdala (a complex of nuclei located in the medial temporal lobe), and it seems to mediate the action of hormones and emotional stimuli on memory consolidation. Norepinephrine plays a prominent role in this activation, inducing a state of hypervigilance that helps recall the event. This mnemonic effect increases when the situation is sufficiently stressful to lead to the release of a substantial amount of corticosteroids, which reach the amygdala. The combination of the two hormones, in this case, has a synergistic effect and leads to memory reinforcement; however, it is interesting to note that increases in corticosteroid levels that are not synchronized with the release of norepinephrine have the opposite effect, that is, they can prevent or suppress its effect on memory.
The amygdala has historically been associated with negative emotions. For example, who hasn’t been startled by those scenes in horror movies where everything is quiet, and suddenly a strange and dangerous creature appears? At that moment, the amygdala is activated, sending a message of imminent danger to other brain areas, which prepare the body for fight or flight. However, although it can be seen as a protective device that prevents the individual from engaging in potentially dangerous behaviors, various studies have verified its participation in processing positive emotions. It has been shown that this structure mediates the associations between sensory input and its positive emotional value, influencing behavioral responses, albeit unconsciously, and proving that its role in this case is at least as important as in negative emotions.
There are other events capable of strengthening or weakening our memories, whether they are natural, such as states of alertness and attention, or artificial, such as the administration of drugs. However, the main modulators of our memory are emotions, as we more easily remember the facts of our lives that have a strong emotional component. This is quite interesting when we consider the fact that our memories are constant guides in our lives, influencing the way we behave, think, make decisions, and interact with one another, especially when it comes to implicit memories (see previous post), to which we do not have conscious access. This leads me to think about the possibility that perhaps we can give a little boost to our memories; that is, if we could create more positive experiences in our lives or increase our good moments, would we have more “positive circuits” in our favor?
References
Joëls M, Fernandez G, Roozendaal B. Stress and emotional memory: a matter of time. Trends in Cognitive Sciences. 2011; 15(6):280-88.
Lent, R. People with history. The neural bases of memory and learning. In: One hundred billion neurons: fundamental concepts of neuroscience (Lent, R.). 2001; p.587-617, Atheneu Publishing.
Murray, EA. The amygdala, reward and emotion. Trends in Cognitive Sciences. 2007; 11(11):489-97.
Figure adapted from: Lent, R. People with history. The neural bases of memory and learning. In: One hundred billion neurons: fundamental concepts of neuroscience (Lent, R.). 2001; p.587-617, Atheneu Publishing.
