Memory. It’s a funny thing. If you looked at a year group photo from secondary school, you could probably name most of the faces staring back at you – and even recall where you sat in each classroom. But the name of the book you just read, or a film you recently watched? Poof, gone. Or perhaps you can remember every word to a song you haven’t heard for years, but find yourself forgetting important things like dates and appointment times.
So why does the brain store certain memories, and let others slip away? It’s not a fault in your wiring, it’s something called encoding. Cognitive strategist Natalie Mackenzie explains that without this, the brain has nothing to retrieve, as the memory was never really stored in the first place. It’s a bit like not hitting the save button on your computer.
‘A classroom seat is tied to social awareness, novelty and repeated experience, all of which trigger deep encoding,’ Natalie says. Watching television, on the other hand, is almost entirely passive. ‘The brain receives the input, but has no emotional or attentional reason to encode it meaningfully.’
As clinical psychologist and neuropsychologist Emma Hepburn explains, memories are made up of lots of different things: ‘Memories from the past are autobiographical memories – stories that you have consolidated over years that are part of your identity.’ Meaningful events, she adds, are more likely to be encoded into memory than everyday, routine ones.
Making memories
Before a memory can be saved, it has to be noticed. Every sound, smell and passing face that’s picked up by your senses is briefly held in your short-term memory, an action lasting only a matter of seconds. Most of this information is discarded almost immediately, like background noise the brain doesn’t think is worth keeping.
But some of it isn’t discarded. That process begins in the hippocampus, which starts building the memory as it happens. If the moment carries enough emotional weight, the amygdala steps in and effectively flags it as important – a stamp that tells the brain, ‘hold on to this one’. Natalie explains that this flagging system is what separates a memory that sticks from one that disappears by the next morning.
Emma adds that the strength of the memory trace also plays a role. A memory trace is the physical or biological change in the brain that corresponds to a memory. It is what allows memories to be stored, strengthened and retrieved later on. Some of your memories are naturally stronger from the outset (such as a song you danced to at your wedding) while others need reinforcing (perhaps through routine or repetition) to stay retrievable. ‘If there is a strong memory trace, for example through repetition, then it is likely to be stored more effectively,’ Emma says, ‘which means it is retained within memory and we can recall or retrieve it later.’
Emotions, sleep and memories
Sleep, it turns out, is where much of that reinforcement happens. Both experts point to the same overnight process: while we sleep, the brain sorts through the day’s experiences and moves the memories worth keeping into longer-term storage. Skip that consolidation window, whether that happens because of a bad night’s sleep or simply because you stayed up too late, and much of what happened during the day is at risk of fading before it’s properly saved. Interestingly, memories don’t sit neatly in one place waiting to be replayed; they’re distributed across networks of connected neurons throughout the brain. Emma describes the hippocampus almost like an index: ‘We think stronger memories tend to be stored throughout the brain within linked neural networks, and our hippocampus acts as a pointer to retrieve these memories and links the neural networks together.’
It’s clear that emotional weight helps decide what gets kept. But new research suggests its influence doesn’t stop there; it can reach backwards and forwards in time, rescuing memories that have nothing to do with the moment itself.
A 2025 study from Boston University, published in Science Advances, looked at exactly this. Researchers found that when something surprising, rewarding or emotionally charged happens, it can strengthen the memory of ordinary, unrelated moments that happened just before or just after it – details that would otherwise have faded completely. Win big on a lottery ticket, for example, and chances are you’ll be able to recall exactly what you were doing in the minutes before, right down to what you were wearing or what song was playing, despite none of it being memorable on its own.
The effect seems to work like a kind of ripple. The closer a mundane memory is to the emotional event, whether that’s in timing or in some shared detail, the stronger the boost it receives; memories that are further removed don’t get the same benefit. And in something of a twist, the effect was stronger for moments that came after the emotional spike than those that came before it. ‘Memory isn’t just a passive recording device,’ says Robert Reinhart, cognitive neuroscientist at Boston University and the study’s co-author. ‘Our brains decide what matters, and emotional events can reach back in time to stabilise fragile memories.’
Your brain as curator
So how does the brain decide what to filter out and what to keep? It turns out your beautiful mind has a built-in system for deciding what to retain. Emma explains that the brain asks a few simple questions when it comes to filing memories: how important is it? How strongly do we feel about it? How often does it happen?
Natalie adds that: ‘Cortisol and adrenaline, released during emotionally charged times, signal the hippocampus to pay close attention,’ she says. ‘Ordinary, predictable and more low-stakes moments don’t trigger those signals, so the brain files those as unremarkable and lets them go.’
Essentially, emotion is the key filing system, which is why something like a first kiss is more memorable than what you had for breakfast yesterday. ‘The brain is very practical about what earns long-term storage and what is worth the encoding effort,’ says Natalie. It’s okay, then, for yesterday’s breakfast to be a blur. Forgetting is the brain’s way of filtering out details to avoid information overload. But the moments that really move you are the ones that tend to stick.
Three ways to work with your memory
- Pay attention to what you want to remember. So much of life is rushed through on autopilot. Emma recommends rehearsing information (for example, writing it down) and actively engaging with it, rather than just repeating it. For example, if you want to remember a name at a party, Natalie suggests using it immediately in conversation, attaching it to something distinctive about the person, like a facial feature or clothing, and saying it again before you leave.
- Get a good night’s sleep. According to Emma, going over information you want to remember before sleep (even just a nap) can help consolidate memories in storage.
- Put the phone down. Natalie believes you cannot be truly present and behind a screen at the same time. If you really want to remember that magical family holiday, it is this presence that creates a memory worth having.