My husband was recently describing something that happened on a past holiday. It wasn’t a significant event, but it sounded pleasant. I, however, had no recollection of what he was telling me. He couldn’t quite believe it.

We know that “recollections may differ”, but how can it be so different? And why do I not have this memory? I’m busy at work – have I simply run out of space?

It’s a tempting explanation. We talk about “full heads”, “information overload”, and “too much to take in” as though the brain were a container that eventually reaches capacity. But the brain does not fill up. Instead, it filters.

At any given moment, far more information is available to us than we could ever realistically store. The sights, sounds and conversations of even a single day would overwhelm any system that attempted to record them in full. Instead, the brain relies on selection. Attention determines what is noticed. Emotion helps determine what matters. Then, structures such as the hippocampus decide what is worth committing to longer-term memory.

If your attention is elsewhere, the process falters at the first step.

On that holiday, my husband may have paused long........

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