Imperfect memory and false recollections are essential elements of a flexible mind, argues neuroscientist Charan Ranganath in a new book. David Robson asks him why.

"Memory," writes neuroscientist Charan Ranganath in his new book Why We Remember, "is much, much more than an archive of the past; it is the prism through which we see ourselves, others, and the world."

Ranganath is a professor of psychology at the University of California, Davis who has spent the past 30 years exploring the brain processes behind our ability to recall, remember – and forget. He argues that many of our common assumptions about memory are misguided; its apparent flaws often arise from its most useful features, creating a cognitive flexibility that was essential for our survival.

He spoke to science writer David Robson about this cutting-edge understanding of the brain, and the ways that we can use this knowledge to make better use of our perfectly imperfect minds.

Your book is full of counter-intuitive notions. Let's begin with the idea of "error-driven learning". Why do we learn best when we allow ourselves to make mistakes? 

Memories are formed through changes in the strength of connections between neurons. Now, some of these connections are not going to be optimal, when others are going to be stronger and more effective. The principle of error-driven learning is simply that, when you try to retrieve these memories, your recollection is always going to be a little imperfect. And so, when the brain tries to pull up this memory, and you compare it to the real information, these networks can weaken the bad links and strengthen the good links.

The implication is that challenging yourself to pull up the material that you're trying to learn is the best way to learn more, because it exposes those weaknesses, and therefore it gives your brain a chance to optimise these memories. It's why active learning techniques – like driving through a neighbourhood instead of just looking it up on Google Maps, or performing in a play versus reading the script over and over again – are so effective.

Many of us feel frustrated by the gaps in our recall, but you propose that forgetfulness is often beneficial. How come?

An analogy I like to give is to imagine that I went to your house, and asked: why aren't you a hoarder? Why don't you just store everything? If we didn't forget anything, we'd be hoarding memories, and you'd never be able to find what you want, when you want it. 

Right now I'm staying in a hotel, and it just wouldn't make sense for me to remember this room number two weeks from now. Similarly, think of all the people you just pass by on the street. Do you really need to memorise all their faces?

Why do we become more forgetful as we age?

The problem, as we get older, is not necessarily that we can't form memories, but that we're not focusing on the information that we need to remember. We become more distractible, and all this inane stuff comes in at the expense of the important material that we care about. And so, when we're trying to recall these memories, we can't find the information that we're looking for.

What strategies can we use to avoid this and improve the quality of our memories?

There are three basic principles. One is distinctiveness. Our memories compete with each other, and so the more you can make something stand out, the better. Vivid memories that are associated with unique sights, sounds and feelings – they are the ones that are going to stick around. And so focusing on the sensory details, as opposed to being stuck in our heads, really helps us to remember better. 

The second strategy is to encourage greater organisation of your memories in a way that makes them more meaningful. In the book I discuss the "memory palace" method, which involves associating the information you want to learn with information that you already have.

Thirdly, we can create cues. Searching for a memory is very effortful and error prone; it's better if memories just pop into our head. Creating cues can help that to happen. We know, for instance, that songs can naturally evoke memories from particular periods in your life. And there are many other everyday cues you can use. If I'm trying to remember to take out the rubbish on trash day, I'll imagine myself walking to the door, and then I'll look over at the trashcan before walking over to it. As a result, when I come to the door in real life, it will act as a cue that I have to take out the trash.

Besides losing memories, we may find that our recollections include false details that don't correspond to the real events. Why does this occur?  

We have "schemas" that help us to remember with economy. Imagine you have just been to the bank – you already have a whole lot of knowledge about the kinds of events that happen in the bank and the kinds of things that don't. That allows you to restrict the range of the information that you have to remember, with the schemas acting as the connective tissue that allows you to take that new [data] and apply them. But sometimes the schemas fill in too many blanks, with wrong details.

The second reason is that memories change over time. That's very important, because you want to be able to update your memories. If you've seen a relative that you haven't seen in a long time, and their face has changed relative to the first time you saw them, you need to create a more accurate memory of their appearance. But sometimes our imagination can seep into the memory.

In what way is memory a collaborative process? 

When we share memories with other people, it can lead the memories to be updated. When I'm explaining an event to you, the act of making up that story to tell you can change the way that I remember it. Your reactions to the way I tell the story, for example, will shape my memory of it later on; it may become more humorous. Or you might even give me some additional – but erroneous information – that can seep into my memory: I get confused between what actually happened versus what you told me while I was explaining what happened. I would argue that many of our memories are not [purely] our own anymore – they're collective memories.

How has your scientific research shaped your relationship with your own memories?

Writing the book, in particular, has given me an incentive to preserve my memory. I'm trying now to exercise regularly, and I'm very mindful of my diet, to make sure that I maintain my cognitive health in my old age.