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Memory debate focuses on hippocampal role
18 March 2002 10:00 GMT
by Laura Spinney, BioMedNet News
A controversial study suggesting that the hippocampus is required for the
consolidation or filing of memories but not for their lifelong retrieval
is set to fan the flames of a long-running debate about the nature of the
neural substrate of memory.
Somewhere around a decade after a memory is formed, the hippocampus
becomes obsolete in its retrieval, according to Hans Markowitsch, a
psychologist at the University of Bielefeld, who presented his
unpublished evidence on Saturday at a conference on cortical plasticity
in Schwetzingen, outside Heidelberg.
"We think that initially the hippocampus is engaged in consolidating
memory, and thereafter memories are laid down in neocortical networks and
they become active when triggered for retrieval," Markowitsch told
Using functional Magnetic Resonance Imaging (fMRI), he scanned the brains
of 17 healthy people while they recalled autobiographical memories from
different points in their past.
Retrieval of events that had happened in the previous five years
triggered activation of the hippocampus, but towards 10 years and
certainly after 20 years had passed, the hippocampus did not seem to be
required to dredge up memories, says Markowitsch.
He also gave his subjects neuropsychological questionnaires so that he
could match the memories for emotional content. As a result, he says, he
can safely rule out the possibility that the hippocampus selectively
processes more or less emotional memories.
Markowitsch is not alone in suggesting that the role of the hippocampus
is only in the consolidation of memories. The view is shared by Eric
Kandel, professor of physiology and psychiatry at Columbia University in
New York, who shared the Nobel Prize for Medicine in 2000.
Others claim that the part played by the hippocampus in retrieval is not
time-limited, but lifelong - at least for autobiographical memories.
In direct contradiction to Markowitsch's latest findings, Morris
Moscovitch, director of the Memory Lab at the University of Toronto, has
found similar patterns of brain - and specifically hippocampal -
activation associated with both old and new memories.
One problem with this kind of study, says Moscovitch, is that old
memories tend to lose their perceptual richness and to be less vivid than
newer ones - so are perhaps encoded more semantically than by perceptual
It is therefore difficult to say whether age or vividness is a better
predictor of hippocampal involvement. Indeed, says Moscovitch, there is
evidence that vivid memories trigger hippocampal involvement even when
they are very old.
Nevertheless, he adds, the debate is important - not least because it
suggests alternative explanations for why memory fails in old age and
"Old memories are better preserved than recent ones - or at least so it
may appear," he said. "What we are arguing is that it depends on how
memory is tested and on the kind of memory that is sampled."
Markowitsch is now starting a new study with people he first interviewed
12 years ago, after they had fled from East Germany just before the
Berlin Wall came down.
This time round, he will interview them while simultaneously scanning
their brains, to find out whether particularly emotional memories are
organized differently in the brain to less emotional ones.
This was distributed via the memetics list associated with the
Journal of Memetics - Evolutionary Models of Information Transmission
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