Fwd: Memory debate focuses on hippocampal role

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Date: Fri Mar 22 2002 - 12:33:34 GMT

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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    unpublished evidence on Saturday at a conference on cortical plasticity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
    BioMedNet News.

    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
    For information about the journal and the list (e.g. unsubscribing)
    see: http://www.cpm.mmu.ac.uk/jom-emit

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