A while back this writer was working on a novel, set in Cork during the mid-1990s. One scene revolved around the social welfare office on South Main Street.
I recalled the place with perfect clarity: it was just up from the Beamish Brewery, on the left as you went towards town; the building set maybe half-a-storey below street-level; you walked down a sort of ramp to reach it. That grey, depressing building, the yard out front, the dip down to it: all were as clear as day in my memory.
Except the building didn't actually exist.
Certainly, there is a dole office in Cork city centre; but it's a few streets away, at street-level. It doesn't remotely resemble the one that was being supposedly 'remembered' but was, in fact, being invented.
That's the thing about memory: it's not a burned-on-DVD recording of the past. It is, rather, more akin to a story we tell ourselves anew each time we recall one, as detailed in a very interesting book on memory, Pieces of Light, by Dr Charles Fernyhough.
The Cambridge graduate of Natural Science and Developmental Psychology explains: "We have a good scientific picture now of how memory works; certainly we know what it's not. It's not a record of the past. It's a reconstruction, not a reproduction.
"The story we tell ourselves is generally true, but the details are often inaccurate. We get the past pretty much right, but bits of it might come from somewhere else: a separate memory, something we saw on telly. The boundaries of memory are permeable, and sometimes a new element will creep in. It's like a mutation in the DNA; a mistake can propagate and become part of the memory.
"Even flashbulb memories, of huge events, are often wrong. Lots of people think they remember seeing the planes hit at 9/11, but most weren't watching TV at the time; they saw it later."
In one sense, Charles says, after a long enough time we're no longer remembering the original event, but the memory of the last time we recalled it: a copy of a copy of a copy.
Pieces of Light is a fascinating book because memory is a fascinating subject. Dr Fernyhough asks profound questions: what is memory, what does it mean, how does it work, what does it say about us as individuals?
Naturally, some remain unanswered; they're probably unanswerable, which makes the book all the more mysterious and magical.
One distinction that can be clearly made is between episodic and semantic memory: something happening to you, versus a known fact. (Charles points out that psychologists have identified 256 different kinds of memory, but this is a vital one.)
"The two can overlap," he adds. "Autobiographical memory, the type I'm most interested in, could draw on episodic and semantic. So you might remember an event by thinking, 'I was in such-and-such and it looked like this and the day was warm', but also information about yourself that you know is fact: 'I was living in France and going out with a certain person' and so on. You'd combine them.
"And when we remember, we pull in information not just about the core event but all the sense information around you. You mightn't be aware of noticing, say, a certain smell at the time, but it somehow got into the memory and now can act as a cue to it. Places in particular can be very strong cues; going back there can remind you of what happened."
Charles has "always been interested in memory, pondering the stages of my own memory and questioning how much we can trust these experiences as facts about the past. Why do we remember? What is memory for? It might be about predicting the future as much as recalling the past. It wasn't meant to be perfect; it's a tool.
"I was put off memory when studying psychology, for the same reason it now attracts me. It seemed to be very much about individual narratives, which is difficult to be scientific about. But they're now the aspects that interest me most. I love personal stories and getting inside memory by asking people to describe their experiences."
One thing he noticed during his research was that people tend to be strongly attached to early memories, and get upset when they find out those were largely reconstructed.
"Some of it is sentimentality or nostalgia for the past," Charles says. "Some is because memories are very much tied up with our sense of self. Many great writers, such as Virginia Woolf, say the point they started remembering was also the point they became who they are.
'Several people told me they have vivid memories of being a baby, and maybe it's possible under certain circumstances. Our memories don't trick us wholesale; we're not simply making things up.
"We put together different bits of information. It's a complex machine, but not broken; it works pretty well most of the time.
"So we shouldn't throw out those memories wholesale, but just have a different relationship to them. Take them with a pinch of salt and see them as interesting constructions which tell you something about who you are, rather than a literal report of the past."
Ultimately, he says, we remember stuff that's important to us. "When I was younger I could quote film scripts to the point of tedium! Now my kids do the same and I think, 'How on earth did you remember that?' Of course, they don't have to think about all the things adults have to; they have the mental space to do it."