Hippocampal Activation for Autobiographical Memories over the Entire Lifetime in Healthy Aged Subjects: An fMRI Study

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Abstract
We used functional magnetic resonance imaging to determine the cerebral structures required during the recollection of episodic autobiographical memories according to 5 time periods covering the whole lifespan to test the 2 concurring models of memory consolidation, which propose either a temporary (standard model) or a permanent (multiple-trace model) role of the hippocampus in episodic memory retrieval. The experimental paradigm was specially designed to engage subjects (67.17 ± 5.22 years old) in the retrieval of episodic autobiographical memories, whatever the time period, from personally relevant cues selected by questioning a family member. Moreover, the nature of the memories was checked at debriefing by means of behavioral measures to control the degree of episodicity. Behavioral data showed that recollected memories were characterized by specificity and details whatever their remoteness. Main neuroimaging data (Statistical Parametric Mapping 99) revealed the activation of a network including the left superior frontal gyri, bilateral precuneus/posterior cingulate and lingual gyri, left angular gyrus, and left hippocampus, although the subtraction analyses detected subtle differences between certain time periods. Small volume correction centered on the hippocampus detected left hippocampal activation for all time periods and additional right hippocampal activation for the intermediate periods. Further confirmation was provided by using a 3-way analysis of variance on blood oxygen level–dependent values, which revealed hippocampal activation whatever the time interval. The present data challenge the standard model of memory consolidation and support the multiple-trace model, instead. The comparison with previous literature stresses the idea that a bilateral involvement of the hippocampus characterizes rich episodic autobiographical memory recollection.