. . . At a deeper, biological level, all your memories are fallible. The act of remembering an event from your past is not like playing back a mental videotape in your mind’s home theater system. It is more like retelling a shaggy dog story that you once heard. You recall a few key phrases and junctures along with the story’s overall gist, but you don’t recall the exact order of words in the story. When you repeat the “same” story to another person, you reconstruct it in your own way. You freely embellish and fill in missing gaps to make the story flow smoothly. While you might repeat verbatim a few key bits of the original telling, most of the word choices are yours.
Similarly, when your brain lays down a new memory, what it actually encodes is a sparse constellation of personal details and meaningful junctures. When your brain later retrieves the memory, it uses that constellation as a scaffold for reconstructing the original experience. As the memory plays out in your mind, you may have the strong impression that it’s a high-fidelity record, but only a few of its contents are truly accurate. The rest of it is a bunch of props, backdrops, casting extras, and stock footage your mind furnishes on the fly in an unconscious process known as confabulation.
And it gets stranger. Sometimes a feature that was confabulated during one act of remembering gets rerememered during the next act. In the process, the confabulation can become a permanent feature of the memory. It becomes indistinguishable from the original.
Your memory isn’t a partial sketch of the past, it’s a sketch of a sketch of a sketch of a sketch . . . and with every new rendition, more errors can be introduced. Our colleague Joseph LeDoux, a neuroscientist at New York University who studies memory and emotions, says that he used to think a memory was something stored in the brain and accessed when needed. But a researcher in his lab, Karim Nader, convinced him otherwise. Nader demonstrated that each time a memory is used, it has to be re-stored as a new memory in order to be accessed later. The old memory is either gone or inaccessible. Thus your memory about something is only as good as your last memory about it. This is why people who witness crimes testify about what they read in the paper rather than what they witnessed.
– Sleights of Mind by Stephen L. Macnik and Susana Martinez-Conde