In his recent New York Review of Books essay, legendary neurologist Oliver Sacks tackles precisely that, exposing the remarkable mechanisms by which we fabricate our memories, involuntarily blurring the line between the experienced and the assimilated:

It is startling to realize that some of our most cherished memories may never have happened — or may have happened to someone else. I suspect that many of my enthusiasms and impulses, which seem entirely my own, have arisen from others’ suggestions, which have powerfully influenced me, consciously or unconsciously, and then been forgotten.

One phenomenon Sacks argues is particularly common — if not adaptive — in the creative mind is that of autoplagiarism:

Sometimes these forgettings extend to autoplagiarism, where I find myself reproducing entire phrases or sentences as if new, and this may be compounded, sometimes, by a genuine forgetfulness. Looking back through my old notebooks, I find that many of the thoughts sketched in them are forgotten for years, and then revived and reworked as new. I suspect that such forgettings occur for everyone, and they may be especially common in those who write or paint or compose, for creativity may require such forgettings, in order that one’s memories and ideas can be born again and seen in new contexts and perspectives.

So how can a person possibly know if s/he is having an original thought??

Remembering is not the re-excitation of innumerable fixed, lifeless and fragmentary traces. It is an imaginative reconstruction, or construction, built out of the relation of our attitude towards a whole active mass of organized past reactions or experience. . . . It is thus hardly ever really exact.

Can we ever truly trust any memory?

Is it better to replace our memories with computer storage?

http://pandawhale.com/post/23792/scientists-trace-memories-of-things-that-never-happened-nytimescom

This has philosophical ramifications:

http://pandawhale.com/post/24004/can-computers-teach-us-what-it-means-to-be-human