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Abstract:
Studies of amnesia have demonstrated that the hippocampal
formation (HF) is necessary to establish information in long-term
memory.The precise role of the HF in memory, however, is unknown.
We designed a positron emission tomography (PET) experiment with
encoding tasks that permitted the isolation of different mnemonic
processes theorized to be mediated by the HF, namely novelty
detection, associative learning, and depth of encoding. Fourteen
subjects learned pairs of abstract nouns in four different
experimental conditions, i.e., by deep single-word-encoding (1), by
shallow single-word-encoding (2), and by associative learning of
either novel words (3) or previously studied words (4). Pairwise
subtraction analysis of the intersubject averaged PET images
indicated significantly increased blood flow in the HF during
associative learning compared to each of the single-word-encoding
taks. Regional cerebral blood flow in the anterior HF was highest
during associative learning, followed by deep single-word-encoding
and shallow single-word-encoding. Novelty of words had no clear-cut
effect on hippocampal blood flow. We conclude that establishing
associations in memory is a special function of the HF.
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