Hippocampal formation-cortical high-fidelity memory networks in healthy older adults during the mnemonic discrimination task.

Introduction: Fidelity of detailed information retrieved from long-term memory (LTM) declines in aging due to changes affecting learning and remembering processes. Such behavioral deficits correspond with functional alterations in the hippocampal formation. However, it is unclear whether age-related decline in high-fidelity retrieval alters functional connections between hippocampal and cortical regions. Methods: Twenty-two cognitively intact older adults (69.4 ± 4.4 years) completed mnemonic discrimination tasks during fMRI indicating, whether previously encoded targets, lures, or novel objects were old or new. Results: Participants' high-fidelity memory, measured by the lure discrimination index (the proportion of "new" responses to lures minus the proportion of "old" responses to novel objects), was 0.45 ± 0.04 - lower than previously reported scores in young adults. High-fidelity LTM in older adults engaged a hippocampal formation region in the left entorhinal cortex with trial-wise beta-series connections to the right angular gyrus and the left precuneus. Discussion: Taken together, we characterize the distribution of medial temporal lobe (MTL)-cortical networks in older adults that underlies high-fidelity memory.