What if you could remember everything?

Can you remember what you ate for breakfast? What about a week ago?

Your brain keeps some memories and lets others fade. What if you remembered everything?

What did you have for breakfast today? Easy. What about on this day last month? Probably not. Your brain keeps some memories and quietly lets others fade away.

Now imagine you could remember everything, forever. You'd never forget a fact for a test or a friend's birthday. But you'd also remember every boring bus ride and every out-of-date detail. Would that be a superpower, or a problem? In this lab we follow three clues: why forgetting can help, how memories form, and memory tricks that work.

We tend to treat forgetting as a failure. Neuroscientists Blake Richards and Paul Frankland of the University of Toronto argued in a 2017 review in Neuron that this view is incomplete: the brain has mechanisms that actively promote forgetting, and they may serve an important purpose.

This thought experiment asks what a mind with total recall would be like. It follows three threads: the possible benefits of forgetting, how memories are formed and strengthened, including during sleep, and which study techniques the evidence supports. Sources include the University of Toronto, UC Irvine's Center for the Neurobiology of Learning and Memory, NIH and the Association for Psychological Science.

A few people can remember what they did on almost any day of their lives!

Scientists call this a super memory for your own life.

A few people really do have extraordinary memories of their own lives. Scientists at the University of California, Irvine, first described this in 2006, calling it Highly Superior Autobiographical Memory, or HSAM. The first person they studied could be given a date and tell you what day of the week it was and what she had done.

Since then, more than 50 people with HSAM have been identified. They tend to spend a lot of time thinking about their past, and they understand the calendar and its patterns in detail. Scientists are still working out how their memories work.

UC Irvine's Center for the Neurobiology of Learning and Memory reports that Professor James McGaugh and colleagues described the first known case of what is now called Highly Superior Autobiographical Memory (HSAM) in 2006, in a participant known as 'AJ,' later identified as Jill Price. Given a date, she could name its day of the week and what she did that day. The condition was first labeled hyperthymesia.

More than 50 individuals have since been identified. They recall specific details of autobiographical events, spend much time thinking about the past and understand calendar patterns in detail. The center notes that screening tests rely on expertise and age and carry cultural bias, so studying HSAM is itself difficult.

If you remembered everything, you would never lose a fact for a test.

But your head might also be full of old, unimportant things!

If you remembered everything, school might feel easier: every spelling word, every fact, every page. But you'd also keep every unimportant detail and every out-of-date fact, like where your class used to sit last year.

University of Toronto scientist Blake Richards says the real goal of memory is to help us make good decisions. 'It's important that the brain forgets irrelevant details,' he explains, so it can focus on what helps in the real world. If your brain kept bringing up lots of conflicting old memories, deciding what to do could get harder.

Richards and Frankland's 2017 review frames memory as a tool for optimizing decisions, not for preserving an accurate record. In a changing world, old information becomes outdated; if the brain repeatedly retrieved multiple conflicting memories, informed decisions would be harder.

Their second argument borrows a concept from artificial intelligence, regularization: models generalize better from large amounts of data if some detail is forgotten, so the core information needed for decisions stands out. Total recall, by this reasoning, might hinder generalization. Whether people with HSAM actually decide or generalize differently is not established by these sources; it remains an idea.

Your brain makes new memories all day. When you sleep, it decides which ones to keep.

Sleep helps you remember what you learned!

All day long, your brain forms new memories, and most of them will fade. A part of the brain called the hippocampus is key for making new memories. Then, when you sleep, NIH reports, the brain goes back through recent memories and decides which to keep, making some stronger and linking them to older ones.

Forgetting isn't always an accident either. Paul Frankland's lab at the University of Toronto and SickKids found that new brain cells growing in the hippocampus seem to help us forget. Young people grow more of these cells, which may be one reason adults rarely remember anything from before age four.

NIH News in Health (2013) summarizes sleep research: memories first form in a raw, fragile state; sleep before learning prepares the brain to form memories, and sleep after learning helps consolidate them. Sleep researcher Robert Stickgold describes sleep as a time when the brain revisits recent memories and decides what to keep. Sleep loss affects the hippocampus, key for new memories, and can cut the ability to learn by up to 40 percent.

Forgetting has its own mechanisms. Frankland's lab found that new neurons generated in the hippocampus seem to promote forgetting; because this region produces more new cells in the young, the finding may relate to why adults typically lack memories of events before about age four.

Want to remember something? Test yourself! Try to remember it without looking.

And practice a little bit on different days.

You can't remember everything, but you can remember what matters better. The Association for Psychological Science reports that testing yourself, trying to recall something without looking, is one of the most effective ways to make it stick. In a famous study, students learning word pairs who kept testing themselves remembered more a week later.

Spacing helps too: practicing a little on several days works better than cramming all at once. And don't forget sleep! Researchers say the sleep you get the night after studying matters at least as much as the night before.

The APS Observer (2016) describes testing as one of the most effective techniques for committing information to memory. In Karpicke and Roediger's study of Swahili-English word pairs, learners who kept testing themselves on every pair remembered more vocabulary a week later than those who stopped testing items once recalled.

Soderstrom, Kerr and Bjork (2015) showed that part of that benefit came from spacing, the time between repetitions; when spacing was controlled, restudying also improved learning. Add sleep: Stickgold advises that the night after studying matters at least as much as the night before. Selective, well-spaced retrieval may serve learners better than trying to keep everything.