Why We Forget

For most of history, forgetting has been seen as a failure: a sign that the mind is not working as it should. We apologise for forgetting names, worry when we misplace our keys, and spend a great deal of money on courses and apps that promise to improve our memory. Yet a growing number of scientists argue that forgetting is not a flaw in the system at all. In my view, they are right: forgetting is one of the brain's most useful features.

The first systematic study of forgetting was carried out in the 1880s by the German psychologist Hermann Ebbinghaus. Using himself as the only subject, he memorised lists of nonsense syllables and tested how many he could recall after different periods of time. He found that memory declines rapidly at first, much of what is learned is lost within a day, and then more slowly. This pattern, now known as the 'forgetting curve', has been confirmed by many later studies. Ebbinghaus also discovered that reviewing material at increasing intervals greatly slowed the rate of forgetting, an insight that underpins modern 'spaced repetition' learning apps.

Why should the brain discard information so readily? One explanation is that memories simply fade over time, like footprints in sand. However, this theory has been difficult to prove, and many researchers now believe that interference plays a larger role. When we learn something new, it can compete with, and partly overwrite, older memories that are similar. A student who learns Spanish vocabulary after studying Italian, for instance, may find the two languages blur together.

More recently, neuroscientists have suggested that forgetting may be an active process. Experiments led by Professor Kenji Ito suggest that the brain contains mechanisms whose job is to remove memories. In studies with mice, his team identified a protein that gradually weakens the connections between the brain cells that store old memories. When the protein was blocked, the mice remembered more, but they also found it harder to learn new routes through a maze, as if old knowledge was getting in the way.

This points to an important idea: forgetting helps us adapt. The world changes constantly, and remembering every detail of the past would make it harder to respond to new situations. Dr Samuel Okafor, who studies decision-making, found that people who forgot specific details more readily were often better at identifying general patterns. In his view, a perfect memory would be 'like a map so detailed that it is useless'.

Sleep also appears to play a key role in deciding what we keep. According to Dr Elena Marsh, during deep sleep the brain replays the day's experiences, strengthening those likely to be useful and allowing others to weaken. Her experiments showed that students who slept after studying remembered more of the key concepts, but fewer of the trivial details, than those who stayed awake.

Not all memories are treated equally, of course. Professor Ruth Lindqvist has shown that events connected with strong emotions, whether happy or frightening, are forgotten much more slowly than ordinary ones. This makes evolutionary sense: remembering where danger lies is more important than remembering what we ate for breakfast.

None of this means that we should stop trying to remember. For students preparing for an exam, the lesson is not to fight forgetting but to work with it. Reviewing new material shortly after learning it, and then at gradually longer intervals, takes advantage of the brain's natural rhythms. Cramming the night before, by contrast, may produce good short-term results but is unlikely to lead to lasting learning. Personally, I find it reassuring that a little forgetting is a sign of a healthy mind rather than a failing one.