Imagination
& Memory: Two Sides of the Same Coin
Memory decline in old age may also mean a less vivid
imagination.
Old age does more than stealthily steal
away our most cherished memories: it also seems to diminish our ability to
imagine things. This finding, detailed in the January issue of the journal Psychological
Science1, supports the ¡¥prospective brain¡¦
hypothesis, the idea that imagining the future and remembering the past rely on
the same neural machinery. ¡§One implication of this study is that imagining is
quite closely related to, and dependent on, remembering, perhaps more so than
we previously realized,¡¨ says Dan Schacter of Harvard University.
In the study, Schacter and his team
asked groups of young and old participants, with average ages of 25 and 72,
respectively, to recount a personal episode from their past or imagine a
personal experience in their future in response to cue words. Details in the
participants¡¦ narratives were categorized as either 'internal' or 'external'.
Internal memories are similar to scenes from a movie: they contain specific
subjects and take place in particular settings and time periods. External
memories consist mostly of general facts about the world, such as 'the sky is
blue'. As expected, results showed that the past accounts of the older participants¡¦
tales contained fewer, and less detailed, internal memories than those of the
younger group. This deficit also extended to their future imaginings.
A young participant asked to imagine a
personal scene in response to the cue word 'engine', for example, might
envisage themselves driving in a red convertible along California¡¦s Pacific
Coast Highway one weekend over the summer. They might describe seagulls
circling overhead, the feel of the wind mussing their hair, and the smell of
the salt air as they round a particular corner. In contrast, an older
participant¡¦s response to the same cue word was: "The scene is I¡¦m just
driving along, in the Saab, and ¡K not worrying about high energy costs ¡K" It
wasn¡¦t that the older group had trouble speaking or spoke less, the researchers
found. The older people scored normally on verbal tests, and they talked at
length about non-personal external memories.
Brian Levine, a neuroscientist at the
University of Toronto in Canada, is convinced that the data show a real decline
in personal future imaginings. ¡§I think that methodologically they have ruled
out the other possible explanations,¡¨ Levine says. He adds that the findings
are consistent with other studies examining future thinking in humans.
"The more interesting question is 'why?'," he says.
The researchers speculate that personal
memories are particularly susceptible to ageing because they rely heavily on
'relational processing', the ability to mentally summon and join unique pieces
of information, such as where and when an experience occurred. Stitching the particulars
of a scene together, be it real or imagined, gets more difficult with age.
Over the past year, the prospective
brain hypothesis has gained steady support among neuroscientists. An intriguing
possibility raised by the hypothesis is that the primary role of human memory
may not be to remember the past, but to imagine and prepare for the future. ¡§Once
things in the past are finished, there¡¦s nothing you can do about them,¡¨ Levine
says.
References
Addis,
D.R., Wong, A.T. & Schacter, D.L. Psychological Science. in press
(2008).
Taken from
Nature.com, 4th January 2008
http://www.nature.com/news/2008/080104/full/news.2008.408.html