A reminder of the joy and sorrow of reminiscence.
Why Life Speeds Up As You Get Older: How Memory Shapes Our Past
- Douwe Draaisma
The science of memory has so far been particularly successful when it has neglected actual memories. The reasons for this have changed over time, yet the paradox remains. Hermann Ebbinghaus, the influential founding father of systematic research into human memory, selected nonsense syllables as study material. This is partly because he wanted to use quantifiable, reproducible stimuli, but also because he was keen to get rid of semantics and to eliminate confounds of associativity in encoding and reconstruction in recall. But real-life memories are all about content — take it away and you are left with mental oblivion.
Animal research didn't fare much better, although it had a more excusable reason: it is inherently more difficult to know what it is like to recollect like a bat than to identify with a recollecting human. The development of simple conditioning paradigms provided an effective way to study performance without having to rely on what the behavioural act means to the brain that commands it. Not surprisingly, it took generations, and thousands of publications, before mainstream animal learning research agreed to consider conditioned animals as knowledge systems, rather than as contentless automata.
On top of all this came the remarkable success of molecular and cellular neurobiology, which often confused plasticity with memory. Memory is specific information about past events, whereas plasticity is believed to be the neuronal property that allows information to be retained over time. Many impressive research articles that claim to deal with memory actually deal with plasticity; their authors seem to have forgotten the distinction.
Some students of human memory prefer to use the term ‘memory’ only for mental time travel to the personal past, usually involving some re-experienced emotion: I recall, therefore I re-enact. This is bona fide ‘episodic’ memory. Others take memory to include every type of acquired information that is transparent to conscious awareness, even if this information does not stem from a unique personal experience and there is no mental time travel. This is ‘semantic’ memory. The textbook adjective for all types of conscious memory, including both episodic and semantic memory, is ‘declarative’; ‘non-declarative’ refers to all forms of bodily memory, such as habits and modified reflexes, in the performance of which we often behave like zombies.
Humans fear most losing their declarative memories, especially their episodic memory. There is, however, an inverse correlation between the importance we assign to this type of memory in our own brain and our ability to study it in the brains of others. Episodic memory has proved rather resistant to objective investigation. I am not referring here to the current ‘neophrenological’ wave, in which beautiful false-colour images of brains in action may entice us to believe that we really understand the computational goal of the memory system and the algorithms used to achieve it.
It is refreshing, then, to encounter Douwe Draaisma's book, which reminds us that an interest in memory is primarily synonymous with a wish to understand the joy and sorrow of personal memory. By this we mostly mean memory of personal episodes, which cohere while continuously undergoing both implicit and explicit processing, to yield an autobiographical narrative for the rememberer.
No two brains have identical episodic recollections and autobiographical narratives. These are our unique mental ‘brainprints’. How are these memories formed? Why are some episodes easily recalled, whereas others are forgotten, some only to be recalled later, out of the blue? How can we retrieve complex scenes within a fraction of a second — and why can't we be sure they recapitulate reality faithfully? (They don't.) And why does memory at an advanced age display a bias for recollections from adolescence (the reminiscence effect or ‘bump’)?
Draaisma, a historian of psychology at the University of Groningen in the Netherlands, addresses these and other marvels of personal memory in his charming collection of essays. Combining impressive scholarship in the history of psychology and contemporary research with a poetic touch, he discusses the questions outlined above. But he also considers a range of phenomena from exceptional memory and déjà vu to near-death experiences — are we really granted a fast panoramic view of our life seconds before we depart from this world?
The reader should not expect to find here a systematic account of the field of episodic memory, nor extensive coverage of the literature. Rather, this is a fine collection for memory lovers who will appreciate the facts it contains as well as the rich metaphors, which were to be expected in the light of Draaisma's previous book, Metaphors of Memory (Cambridge University Press, 2000).
Having said that, even memory researchers might find it a useful reminder of phenomena that have drifted away from the mainstream of the collective scientific memory. The chapter ‘Why do we remember forwards and not backwards?’ is just one example. I found myself going to the original paper (Bradley, F. H. Mind 12, 579–82; 1887) and was soon discussing it at a research seminar. Introspection — a research methodology that seems to have recently regained some of its former glory — tells us that we do indeed recall forwards and not backwards, but this holds only for short episodes. Can time's arrow be the defining attribute of a core episodic item, or ‘episodic quantum’? Is there a dedicated brain circuit that subserves this temporal tagging? If so, how is it done and are there pathologies that scramble it?
But you don't have to contemplate enigmatic research questions to enjoy this book. Some essays are touching indeed. In ‘Why life speeds up as you get older’ (which gives the book its title), Draaisma cites a letter from a patient suffering from Alzheimer's disease who no longer remembers that her husband died eight years ago, and keeps writing him heartbreaking letters. Reading this left me not only with a semantic trace, but also with an episodic one. I suspect it will do the same to other readers as well.
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Dudai, Y. Touching memories. Nature 434, 823–824 (2005). https://doi.org/10.1038/434823a
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DOI: https://doi.org/10.1038/434823a