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Charan Ranganath, memory expert: ‘There are leaders who weaponize nostalgia to gain power and manipulate people’

In his new book, the American neuroscientist explores all the recent advances in the study of how human beings retain information

Charan Ranganath
Charan Ranganath in a photo provided by the neuroscientist.

At the end of the 19th century, a German psychologist named Hermann Ebbinghaus invented a method to study human memory using his own mind as the only resource. For hours, he memorized meaningless three-letter words called “trigrams,” each composed of a vowel between two consonants, for example DAX, REN and VAB. He found that he could only memorize 64 trigrams in each 45-minute session before his mind gave out. His efforts revealed fundamental aspects of human memory, including the concept of the “forgetting curve,” which represented for the first time how quickly we forget information.

This story is included in the book Why We Remember by neuroscientist Charan Ranganath. Ranganath is a pioneer in using functional magnetic resonance imaging (fMRI) to study how we remember past events. In his work, he addresses an essential and enigmatic question that Hermann Ebbinghaus raised more than a century ago: “Much of what we experience today will be lost in less than a day. Why?”

Question. In Why We Remember, you argue that the brain is programmed to forget. What is the logic behind this evolutionary mechanism?

Answer. Our brains are neurobiologically predisposed to form and retain memories for information that is important. The brain preferentially forms episodic memories during events associated with surprise, curiosity, joy, desire, love, fear, anger, or stress. These emotional states are associated with the release of neuromodulators — brain chemicals like dopamine, noradrenaline, serotonin, and cortisol — that promote plasticity, meaning that they allow neural circuits to be shaped during learning, ensuring that those memories can stick around.

That can’t be the whole story, however. Memories compete with one another. For instance, we have trouble remembering where we put our keys because we have put our keys in many different places in the past. That competition between old memories and the new one you are trying to form can lead to forgetting — we call that “interference.”

Q. Is it possible to overcome this “interference”?

A. Interference can be overcome. We know that people can feel like they have forgotten something, but then the memories can come back when someone is given the right cues in the right context. For instance, many of us have had the experience of hearing a song, or being in a place, or smelling food that brought us back to a past place and time, opening us up to memories.

Q. Like Proust’s madeleine.

A. Exactly.

Q. Are there psychological or neurological benefits to remembering sad or traumatic events?

A. There can be benefits to remembering painful events if we can learn from them — sometimes you can learn from mistakes that you made in the past, and sometimes the lesson is that you are resilient and able to overcome adversity. And sometimes when we experience terrible events, we can later get enjoyment in telling humorous stories about how badly things went.

Q. Is nostalgia necessarily negative?

A. Nostalgia can be good, in the sense that recalling positive events can make you feel better in the here and now. Nostalgia is only bad when it distorts your view of the past and the present. When we engage in nostalgia, we often overlook the negative events that took place in the past or remember them in a more positive light. That can give you the misleading impression that our lives were better in the past than they are at present. And at the collective level, authoritarian leaders all over the world distort history and weaponize nostalgia in order to gain power and manipulate people. So, nostalgia can be healthy, but we need to be mindful of the potential for it to turn ugly.

When we are feeling angry with someone, we have a natural bias to recall information that reinforces our negative feelings.

Q. After a breakup, why is it common for it to be initially difficult to remember the happy moments? Why do we only remember the sad ones?

A. When try to recall past events, research shows that we are biased to find memories that are congruent with how we feel and think in the present. Our emotions form a powerful part of our mental states, so when we are feeling angry with someone, we have a natural bias to recall information that reinforces our negative feelings, and we are less likely to recall the happy moments.

Q. Recent advances in neuroscience have revealed that it is possible to selectively “erase” traumatic memories in animal models. Based on these findings, what is your perspective on the ethical and practical implications of applying similar techniques in humans to treat disorders such as PTSD (Post Traumatic Stress Disorder)?

A. It’s not clear how well the neuroscience research that is done in rats can generalize to humans. A lab rat remembering that they got an electric shock in a box is probably not comparable to the traumatic memories of a soldier who spent a year in combat or a girl who was repeatedly abused by her parents throughout her childhood. So it is not surprising to me that the results in neuroscience have been hard to translate to PTSD treatment.

But if the barriers can be overcome, we need to think carefully about the goal. I do not think that we should delete memories of negative events, even if they are quite traumatic. However, treatment should be focused on changing the most distressing components of those memories — the parts that lead us to feel the painful emotions every time we remember. We are seeing hints that psychedelic therapies for PTSD might have this effect, by allowing people to remember traumatic memories without the severe pain, fear, and shame.

Q. Therefore, in your opinion, we should not try to erase memories that cause us pain.

A. Our memories of what happened in the past are different from the way in which we feel when we remember those events. I would advise people that, rather than ridding themselves of the memory, it is better to focus on changing your perspective and questioning your beliefs about the event. So I recommend sharing memories in the context of supportive, trusting relationships. When we get outside perspectives, such as what happens in psychotherapy and support groups, it gives us a chance to transform our memories, so that we can see the past in a way that is less distressing.

Q. Why do we sometimes forget what we were going to do when we enter a room or even why we are even there?

A. This happens because our memories are tied to a sense of the place, time, and your mindset during that event (which we call the “context”). When our context changes, such as when we leave the room, or change the topic of conversation, memory researchers would call that an “event boundary,” meaning that the brain forms different memories for the events that took place before and after the context changed.

Suppose you are in your bedroom and you realize that you left your phone in the kitchen. Once you walk out of the room and down the hallway, your context (i.e., your sense of where you are) has changed. So, when you get to the kitchen, the memory for why you went to the kitchen is associated with your memory of being in the bedroom. This means you have to mentally traverse that event boundary in order to pull up the memory from back when you were in the bedroom.

By attempting to record every moment, we do not focus on any aspect of the experience in enough detail to form distinctive memories that we will retain.

Q. In the digital age, we document our lives with our cell phones in minute detail. Does this have any impact on our natural ability to remember?

A. Digital documentation can enhance memory if it is used consistently with principles that help us remember, but we often use it in mindless ways that impedes our natural ability to remember. We often focus on documenting at the expense of experiencing. For instance, when people take pictures at “Instagram walls” or they go to a concert and record it on their phones, their attention is directed to what is happening, but it takes them away from what is distinctive in the moment — the sights, sounds, smells, and feelings that make an experience unique and memorable. By trying to record every moment, we don’t focus on any one facet of the experience in enough detail to form distinctive memories that we will retain. So even if you look back at those pictures and videos that you have taken (and most of us do not), they won’t evoke the same warmth or joy as they would have if you’d kept your phone in your pocket and immersed yourself in the moment.

Q. What would be the correct way to use technology?

A. Thoughtfully taking pictures or videos at opportune moments can orient us to what is interesting and distinctive around us. My daughter, for instance, likes to selectively photograph plants and flowers that catch her eye on our nature walks, which allows her to pause and fully take in those aspects of the scenery at that moment. And later on, if you take a moment to use those photos to cue you to recall that event, you will find that the event will become more memorable and easier to pull up again and again.

Q. Compared to the storage and recall capabilities of digital memory, is human memory becoming obsolete? How do the two compare?

A. The two are very different. I like to say that, “My phone has a photographic memory, but I don’t, and that’s ok.” Digital devices record every bit of information that comes in, but the human brain records memories that prioritize the most novel, surprising, or emotionally significant parts of our experiences. The human brain has also evolved in a way that allows us to learn quickly, but also to be flexible and rapidly adjust our behavior when situations change. And these characteristics help explain why powerful AI systems like ChatGPT, which have a massive carbon footprint and require a massive amount of data, cannot solve certain tasks accomplished by the human brain using enough energy that would be barely enough to power a light bulb.

Q. What do you consider to be the main disadvantage or limitation of human memory?

A. As we have worked on computational models of the brain, I have come to learn that it is very hard to judge a brain system as being good or bad, or having strengths or weaknesses — there is no way to optimally design a brain for every possible goal, any more than you could design a car that has perfect fuel economy, high speed, and the ability to carry a massive amount of cargo. So there are always tradeoffs.

That said, I believe that our greatest limitation is the bias to remember events in a way that conforms to our beliefs. That bias gives us overconfidence in our abilities, leaves us open to prejudice, makes us vulnerable to misinformation, and deprives us of opportunities to learn from our mistakes.

Q. Another limitation of human memory is the general absence of memories from our early years of life.

A. The research shows that a child has no episodic memories, which is known as “infantile amnesia.” During the next two years, a child can form episodic memories, but they are fragmented and blurry, and this is called “childhood amnesia.” During this period, the brain is reorganizing at a rapid rate. The hippocampus and prefrontal cortex, two areas critical for episodic memory, are at very early stages of development. As a result, memories are being built on top of sand that is constantly shifting.

Q. What do you recommend to maintain good brain health and what factors can negatively affect it?

A. There are many factors, and more and more information is coming in about brain health. The biggest advice I can give is that your mind, brain, and body are all connected. So, pretty much anything you can do to take care of your mental and physical health would be a good investment towards brain health.

Some protective factors along these lines are a healthy diet, exercise, social engagement, and sleep. Factors that can negatively affect brain health include common health issues like diabetes and vascular disease, chronic stress, insomnia, depression, alcohol abuse, infectious diseases like long Covid, and even gum disease. Fortunately, unlike the United States, many people in Spain engage in regular exercise by walking and cycling, and many adopt a variant of the “Mediterranean diet,” which has been shown to be very effective in promoting brain health.

Q. After so many years researching human memory, what do you think is the big question that still remains to be answered?

A. This is the hardest question of all! I feel that every real discovery leads us to more questions that we hadn’t thought of asking before. The question I like to ask is: what is the best way to challenge my beliefs about how memory works? The biggest mysteries concern how we use memory in the real world — how we navigate from place to place or understand what is going on in a basketball game or manage to follow what is going on during a stressful conversation. Humans seem to have this extraordinary ability to be able to use our past to build an extraordinary understanding about how everything and everyone is connected. That ability, which allows us to draw a seamless line from the past to the present and the future, is what I want to understand.

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