I jumped on this book when it came out because of several comments I had seen about its theme of memory. All novels are about memory, of course, but this one seemed to be taking seriously a reconstructive view of how we remember: the various ways in which who we are now can change how we make sense of what happened then. On the very first page, the protagonist Tony questions the reliability of his own testimony: 'This last isn't something I actually saw, but what you end up remembering isn't always the same as what you have witnessed.'
And yet the well-documented unreliability of memory isn't quite as interesting to Barnes as its regular habits. When Tony hears about the existence of his late friend Adrian's diary, he wonders whether getting hold of it will dislodge his remembering from the ruts it has been stuck in. Reading Adrian's diary, he thinks, 'might disrupt the banal reiterations of memory. It might jump-start something—though I had no idea what' (p. 77).
Tony is struggling to uncover a truth about the past, and the fact that he always remembers things in the same way is an obstacle to progress. Barnes recognises, even celebrates, the slippery truth of memory, and sees Tony's infuriating constancy of memory as stemming from the habitual nature of his storytelling about the past, rather than from any object-like permanence of his memory representations. Remembering happens in the present moment, and each act of remembering is shaped and constrained by what has gone before. We create memory fictions—the same fictions—so many times over that they come to have a special kind of constancy. It's not that we're laying them down in some permanent store and repeatedly accessing their immutable truths. Rather, we make memories in the present tense, according to the needs of the present. If they tell the same story each time, it's because they are more like habits than things.
The Sense of an Ending presents the most sophisticated view of memory I have seen in fiction for a while, and it offers a nice antidote to descriptions of remembering that liken it to the loading of a mental DVD containing a faithful representation of a past event. On another occasion, the old-fashioned view of memory creeps in, such as when Tony complains (about one episode of forgetting) that 'my brain must have erased it from the record' (p. 119). Memory is not a tape recorder: it has neither a playback head nor a record one, and the analogy is as misleading as it is entrenched.
One of the most interesting parts of the novel describes how a shift in Tony's feelings towards his former lover’s parents unlocks new memories of their relationship:
But what if, even at a late stage, your emotions relating to those long-ago events and people change? … I don’t know if there’s a scientific explanation for this… All I can say is that it happened, and that it astonished me.
Julian Barnes, The Sense of an Ending (Jonathan Cape, 2011), p. 120
I would be the last to want to apply a reductionist method to understanding fiction that's as good as this, but these kinds of circumstance crop up frequently in the modern science of memory. As is the case in memories for trauma, changing your current interpretation of a past event can change the way you remember it. You recall the emotionality of an event differently, for example, according to whether you are asked to recall it from a first-person point of view (where you are more likely to focus on emotions and feelings) or from a third-person perspective (where you are more likely to concentrate on the actual facts of the matter) .
More than just being about memory, though, I think this novel is a return to one of Barnes' favourite themes: that of the self in time. As Tony comments right at the outset, 'we live in time—it holds us and moulds us—but I've never felt I understood it very well.' I recall (probably badly, through the dusty pane of memory) a passage from Barnes' first novel, Metroland, in which the narrator comments that everyone is born to fit best into a particular lifestage. Which means, he expands, that you can come across people in their teens who really would be more at home in their own lives if they were in their forties, so that when they eventually reach that age it's like a homecoming.
I'd love to back this up with a quotation, if anyone remembers it. Tony's problem is that he never quite works out where in his life he fits best. It was that sense of a self trying to find its place in time that struck me most about this memorable literary winner.
 Robinson, J. A., & Swanson, K. L. (1993). Field and observer modes of remembering. Memory, 1, 169-184.