Most memories are accompanied by certain emotions. Good memories of winning a prize by lottery or finding banknotes in your coat pocket in the winter are good emotions, while falling in an interview or losing an important match for a team you passionately support gives you bad emotions. is going to bring This is because the circuits that are activated when good and bad memories are stored in the brain are different. The study was discovered by researchers at the Salk Institute in the United States. The research team also found a substance that connects memories and emotions and published them in the July 20 issue of the international scientific journal ‘Nature’. How does our brain connect and express memories and emotions?
We want to keep the sweet part of our first love as a happy memory for a long time, and we want to quickly forget the unfortunate experience of having a terrible accident. However, the human brain cannot remember everything, so it prefers to remember information necessary for survival. At this time, the brain regards the crisis or fear as very important information and stores it in long-term memory, taking precautions not to repeat the past crisis. That’s why bad memories stay strong for a long time.
Finding neurotransmitters that assign ‘positive’ and ‘negative’ emotions
For a human or animal to learn whether to avoid or seek a particular experience once more in the future, the brain must associate a positive or negative emotion with that stimulus. The brain’s ability to connect emotions with memories is called ‘valence assignment’. The ‘value’, i.e., the ‘valence’, of the positive emotions of a good experience or the negative emotions of a bad experience must be well assigned to the brain so that it can make the right decisions in certain situations. This research by the Salk Research Institute is meaningful in that it uncovered the process of how the brain remembers certain events or experiences as positive or negative.
Already in a 2016 experiment in mice, the researchers found that the pathways in which good and bad emotions are recorded in the brain are different. The answer was found by intensively studying the neurons (nerve cells) of the brain’s basolateral amygdale (BLA), which is the intersection of the circuits that store two types of memories. In the brain of mice, fluorescent substances were inserted into the neurons responsible for good and bad memories, respectively, and the degree of activation was observed through ‘advanced optical genetic equipment’. They gave the rats a loud tone and gave them bitter food to engraved bad memories, or linked a good tone with sweetness to instill good memories.
Experimental results showed that neuronal clusters responded to both good and bad emotions. It was found that good emotions are remembered through the ‘reward circuit’ of the brain, and bad emotions are stored in the ‘fear circuit’ as if there are two lines in the brain. The reward circuit is activated with ‘positive valence’ following a good experience, but is less active following a bad experience. On the other hand, the fear circuit had more ‘negative valence’ activated following bad events and decreased activation following good things. This means that the basolateral amygdala is responsible for allocating the emotional processing ‘value’ of good or bad stimuli.
However, at that time, they did not know which line of the two lines to use at a given time, or what signal of the switch function to indicate it. One of the neurotransmitters, Neurotensin, was chosen by the researchers in this study to determine the operator of that role. Neurotensin is a small substance connected with 13 amino acids, and has arousal functions such as regulating body temperature and appetite, awakening consciousness and increasing attention.
The reason the researchers paid particular attention to neurotensin is that it is produced in nerve cells (neurons) involved in the valence allocation of good or bad emotions. Of course, these neurons also produce other neurotransmitters, but I guessed that neurotensin is likely to play a role in the process of linking memories and emotions.
Neurotransmitters stored in high concentrations at the ends of nerve cells are released from not only the brain but also nerve cells in the body to transmit information to adjacent nerve cells. One nerve cell exchanges information with thousands or tens of thousands of nerve cells. In other words, neurotransmitters are responsible for this information communication. Until the early 20th century, it was thought that the cytoplasm between nerve cells and nerve cells was connected to each other like a power cord to transmit information. However, as a result of close observation under a microscope, it was found that there is always a certain gap (gap) between nerve cells. Therefore, the inference that the existence of a certain medium is necessary for information to be transmitted across this gap naturally emerged.
The key to treating ‘post-traumatic stress disorder’
The researchers selectively removed the neurotensin gene from neurons using the gene scissors CRISPR to observe the changes that occur in the animal’s brain when the neurotensin disappears. They created a mutant mouse that might not produce any neurotensin at all. When neurotensin signaling to the brain’s basolateral amygdala ceased, the mice might no longer assign positive positive valences. The researchers gave the mice a nice tone and associated it with a sweet taste, but failed to assign positive emotions to their memories.
Interestingly, even when the neurotensin gene was removed, the negative valences that assigned negative emotions were not blocked. Rather, the association between the negative stimuli that linked the loud tone to the bitter taste was stronger, assigning more ‘negative valence’. Professor Kay Tye of the Salk Institute, who participated in the study, says the findings suggest that the brain’s default state is biased toward being more sensitive to negative stimuli such as fear. From an evolutionary perspective, this would mean helping people avoid potentially dangerous situations.
The research team then used CRISPR once more to slightly increase neurotensin levels. Then, positive positive valence was allocated to reward circuit, and negative valence of negative emotion was less allocated to fear circuit. Finally, they have pinpointed the neurotransmitter that assigns positive or negative emotions to memory. This is the first time the switch operator neurotensin has been identified.
Postdoctoral researcher Hao Li, the first author of the paper, says that it is possible to switch the neurotensin on and off so that positive or negative learning actually takes place. Therefore, this study is expected to be helpful in developing treatments for mental disorders such as anxiety, addiction, depression, and post-traumatic stress disorder (PTSD). The team’s ultimate goal is to identify new therapeutic targets by continuing to discover other signaling pathways or substances related to neurotensin in the future. They also plan to figure out how humans can remember good memories more strongly than bad ones. As the saying goes that happiness is in the process, we hope that each research process of the research team will become a way to maximize our happiness.
