Our memories form the bedrock of who we are. Those recollections, in turn, are built on one very simple assumption: This happened. But things are not quite so simple. “We update our memories through the act of remembering,” says Charan Ranganath, a professor of psychology and neuroscience at the University of California, Davis, and the author of the illuminating new book “Why We Remember.” “So it creates all these weird biases and infiltrates our decision making. It affects our sense of who we are.” Rather than being photo-accurate repositories of past experience, Ranganath argues, our memories function more like active interpreters, working to help us navigate the present and future. The implication is that who we are, and the memories we draw on to determine that, are far less fixed than you might think. “Our identities,” Ranganath says, “are built on shifting sand.”

But if memories are malleable, what are the implications for how we understand our “true” selves? At the risk of being pretentious, I’ll get philosophical for a second.

You’re not being pretentious. OK, good, because I always have this critical peer reviewer in the back of my head saying, “Don’t say that!” But your question gets to a major purpose of memory, which is to give us an illusion of stability in a world that is always changing. Because if we look for memories, we’ll reshape them into our beliefs of what’s happening right now. We’ll be biased in terms of how we sample the past. We have these illusions of stability, but we are always changing. And depending on what memories we draw upon, those life narratives can change.

Tell me more about what you mean when you say “illusion.” I probably overstated it with the word “illusion,” but there is an illusionary component. I think we have this illusion that much of the world is cause and effect. But the reason, in my opinion, that we have that illusion is that our brain is constantly trying to find the patterns. One thing that makes the human brain so sophisticated is that we have a longer timeline in which we can integrate information than many other species. That gives us the ability to say: “Hey, I’m walking up and giving money to the cashier at the cafe. The barista is going to hand me a cup of coffee in about a minute or two.” This is everyday fortunetelling that we do. There’s nothing that says that the barista won’t throw this coffee at me. There is this illusion that we know exactly what’s going to happen, but the fact is we don’t. Memory can overdo it: Somebody lied to us once, so they are a liar; somebody shoplifted once, they are a thief. If people have a vivid memory of something that sticks out, that will overshadow all their knowledge about the way things work. So there’s kind of an illusion there.

If what we’re remembering, or the emotional tenor of what we’re remembering, is dictated by how we’re thinking in a present moment, what can we really say about the truth of a memory? I think of memory more like a painting than a photograph. There’s often photorealistic aspects of a painting, but there’s also interpretation. As a painter evolves, they could revisit the same subject over and over and paint differently based on who they are now. We’re capable of remembering things in extraordinary detail, but we infuse meaning into what we remember. We’re designed to extract meaning from the past, and that meaning should have truth in it. But it also has knowledge and imagination and, sometimes, wisdom.

I think everyone has seemingly inexplicable memories that stick with us. One for me is, a lifetime ago, sitting in an internship and locking eyes with a person across the room — whom I never spoke to. This two-second interaction is still kicking around in my head 20 years later. What could explain that? Neuroscience is terrible for picking out any one thing and saying why it happened. But if you think about it from an evolutionary perspective, memory, often, is educated guesses by the brain about what’s important. So what’s important? Things that are scary, things that get your desire going, things that are surprising. Maybe you were attracted to this person, and your eyes dilated, your pulse went up. Maybe you were working on something in this high state of excitement, and your dopamine was up. Maybe she had a T-shirt on, and it was like, “Oh, I know about that.” It could be any of those things, but they’re all important in some way, because if you’re a brain, you want to take what’s surprising, you want to take what’s motivationally important for survival, what’s new.

On the more intentional side, are there things that we might be able to do in the moment to make events last in our memories? In some sense, it’s about being mindful. If we want to form a new memory, focus on aspects of the experience you want to take with you. If you’re with your kid, you’re at a park, focus on the parts of it that are great, not the parts that are kind of annoying. Then you want to focus on the sights, the sounds, the smells, because those will give you rich detail later on when you remember it. Another part of it, too, is that we kill ourselves by inducing distractions in our world. We have alerts on our phones. We check email habitually. So you don’t remember being there, because to some extent you were never really there in the first place. If you set time with your child, don’t check email, and turn off your alerts. That’s the idea. Technology can be helpful for memory, but usually not in the way we use it. You’re not really there if you’re mindlessly taking pictures, because it takes over the experience. When we go on trips, I take candid shots. These are the things that bring you back to moments. If you capture the feelings and the sights and the sounds that bring you to the moment, as opposed to the facts of what happened, that is a huge part of getting the best of memory.

I often find myself going back to music that I associate with melancholy memories. Yeah, I mean, you’ve got a legion of Smiths fans all over the world who do that.

In the book, you say this concert is a central memory. It was.

When do you think it happened? It must have been 1985.

People get stuck in memories, whether they’re traumatic or more benignly negative. What are ways people can get unstuck? It’s very hard. You know, the training environment I was in was very down on psychoanalysis, but it always comes back to memory. A lot of that benefit is from the sharing of memories. Maybe it’s a sad memory, but I’m telling you with the goal of helping me get over it. That in and of itself changes my perspective. We know that people tailor their message for the listener. Then you reflect it back to me and reorganize it as an outsider. Once we go back and forth, we’re updating the memory to something that’s no longer my own. It’s now shared. When you tell someone, “You shouldn’t be ashamed,” it changes that whole relationship with the past. The first patient I ever did therapy with, he had a driving phobia. He worked through the behavior-therapy part, which is just drive, drive, drive until you habituate that biological fear response. But he didn’t feel better. Eventually he told me that he had a memory. How much of this was true, how much of it wasn’t, I didn’t know, but it didn’t matter. He was gay, and he came out of the closet with his dad and got into an argument with him and then was in the car afterward and got into a car accident.

Pretty clear! Yeah, exactly. It was about processing that memory and what it meant to him. He hadn’t told this to anyone; I don’t know that he had even thought about it that much. That was deep for me.

Do you think there is some core unchanging self? Something that makes us us? Or is it all just this flowing assemblage of interpretations of memories that make the present make sense? Is that sense of self static? I would say that some parts of it are. Memory gives us the power to shift our sense of who we are. If you believe you’re a failure, a lot of the power of thinking positive is remembering those times when you weren’t and being able to supplement those beliefs. There’s a dynamic sense of the self. I grew up in an immigrant family under challenging circumstances, and that part of myself is locked away from most anyone I interact with. We have these little compartments that are rooted somewhat in memory that we can access at different moments.

This interview has been edited and condensed from two conversations.